Scanning Probe Microscopy in Catalysis

King Lun Yeung and Nan Yao Department of Chemical Engineering the Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong, P.R. China

Since the first successful scanning tunneling microscopy (STM) experiment conducted by

G. Binnig and coworkers at IBM Zürich Research Laboratory in March 1981, STM has proven

to be an important tool for surface and interfacial characterization1. The success of STM has led

to the proliferation of novel local proximal probe instruments including atomic force microscope

(AFM)2, scanning ion microscope, scanning chemical potential microscope, scanning

thermal/thermal conductivity microscopes (STHM/STCM) and scanning near field optical

microscope (SNOM) just to name a few of the more successful designs. The growing family of

scanning probe microscopes (SPM) finds uses beyond surface science and has made significant

contributions to biology, catalysis, electrochemistry, metrology, polymer science, semiconductor

science, micro- and nano-fabrications. SPM is not restricted to the role of passive observer, but

can be used actively to engineer and manipulate the sample surface as in microfabrication. The

direct manipulation of surface atoms into logos and pictures has been made famous by SPM and

illustrates their potential use in the new age of nanotechnology.

Several books and review articles on scanning probe microscopy have been written over

the last two decades since its discovery. They include general topics that address the theory and

operating principles behind the technique, and specialized topics that discuss their application

and use in various disciplines.3-27 This article provides a review of the recent advances in the use

SPM technology for real-time monitoring of dynamic events on catalyst surfaces. The structural

and morphological transformation of catalyst during preparation and pretreatment are discussed

in section 1. Section 2 presents the SPM research on adsorption, diffusion and reaction that are

essential steps in a catalytic reaction, as well as surface reconstruction, annealing, coking and

poisoning that are responsible for loss of catalyst activity. In section 3, we reports the use of

SPM for surface manipulation and their potential use in catalysis research.

1. SPM Observation of Catalytic Surfaces

Tables 1, 2 and 3 list some of the catalytic materials investigated by STM and AFM.

Direct imaging of the surface atomic structure is now a routine practice for most metal and metal

oxide single crystal surfaces under clean vacuum environment. Similar atomic resolution is more

difficult but not impossible to obtain for polycrystalline surfaces and dispersed catalyst particles.

Unlike most surface characterization techniques, SPM can be operated under different gas

environment at higher pressures, but at the expense of poorer resolution. Indeed, SPM has been

used in the study of metal surfaces during metal epitaxy76 and even under electrochemical

conditions77. The information on the surface structure and its transformation is vital to our

understanding of catalysis.206

1.1. Model and Unsupported Catalysts

Scanning probe microscopy has successfully revealed the detailed surface atomic

structures of single crystal surfaces of many catalytic metal and metal oxide materials (Table 1 &

2). Platinum is one of the most studied metal surfaces. The detailed surface structure of Pt(100),

Pt(110) and Pt(111) under ultrahigh vaccum and different gaseous environment at different

temperatures and pressures had been reported. 31,43,71 In a recent review, Somorjai207 summarizes

the use of scanning tunneling microscopy (STM) for investigating CO oxidation on Pt(111), NO

and CO mobility on platinum and rhodium (111), ethylene hydrogenation on Pt, and

hydrogenation and dehydrogenation of cyclohexane on Pt(111) and Pt(100). Besides platinum,

gold is the other most studied metal surface. 31,32,41-53 Au(111) was observed to undergo surface

reconstruction to form a (22×√3) structure in order to decrease its surface free energy as shown

in Fig. 1. 208-210

Titanium dioxide has attracted an enormous research interests in recent years, because of

its potential use for harvesting light for energy production, chemical conversion and pollution

remediation. The (110) crystal surface being the most stable of TiO2 crystallographic planes is

widely used as model catalyst surface and has been investigated by different surface

characterization techniques. This surface possesses two ordered surface atomic structure with

(1×1) and (1×2) symmetries. The (1×1) phase is a stoichiometric and bulk-terminated surface.

Heating the (1×1) phase in ultrahigh vacuum (UHV) or mildly reducing atmosphere leads to

(1×2) surface reconstruction. The reconstructed surface is usually described by either missing-

row or added-row models shown in Fig. 2. The missing row model assumes that the

reconstruction results from the removal of alternate rows of bridge-oxygen (Fig. 2a), whereas the

added-row model proposes that the (1×2) structure arises from adding rows of Ti2O3 (Fig. 2b) or

fully reduced (1×1) phase (Fig. 2c) on top of the TiO2 (110)-(1×1) surface.211-213 Although it is

well accepted that high temperature annealing causes the transformation from p(1×1) to p(1×2)

phase, the details of transitional process are not clearly demonstrated until recently. Asari et al.214

reported the transitional structures between TiO2 (110) p(1×1) and p(1×2). On slightly reduced

TiO2 surface, they were able to identify Ti2O unit rows that corresponded to the p(1×2) rows,

while on the heavily reduced surface they found added Ti2O3 structure proposed by the added-

row model. They observed the growth of p(1×2) phase with Ti2O units from bridging oxygen

rows of p(1×1) phase.

Besides inducing surface reconstruction, oxygen vacancies are created in the rows of

bridging oxygen during the high temperature annealing at UHV.215 These surface defects can

play an important role on the catalytic and chemical properties of TiO2. STM study identifies two

types of vacancies. One of them appears as a bright spot centered among the dark rows, and its

intensity decreases when exposed to oxygen at room temperature. The other shows as a dark spot

among the bright rows of atom and remains unaffected by oxygen. Depending on tip bias

voltage, these vacancies can be moved and even removed from the surface. Fukui et al.117

successfully imaged oxygen point defects on TiO2 (110)-(1×1) surface using non-contact atomic

force microscopy. The re-oxidation of annealed TiO2 (110) surface was investigated by Smith et

al.216 using a variable temperature STM. Surface growth was observed during re-oxidation at

temperatures between 573 to 1000 K and oxygen pressures of 5×10-8 to 2×10-6 mbar. The

adsorbed oxygen combined with the mobile interstitial Ti3+ originating from the bulk material to

form individual TiO2 units. These TiO2 diffused on the surface and coalesced into the observed

(1×1) islands, (1×2) strings and cross-linked (1×2) features shown in Fig. 3. The surface growth

kinetics was obtained by measuring the topography of the growing surface from the successive

STM images (Fig. 3). The growth rate was reported to be a linear with respect to the oxygen

pressure and an activation energy of 25 ± 4 kJ mol-1.216

Practical catalysts used in industry are mostly in powder form that is difficult to image

with scanning probe microscopy. Care must be exercised during sample preparation to avoid

introducing contaminants and artifacts. Also, the complexity of the powder structure makes data

interpretation difficult. This can be partially overcome by supplementing the STM data with

information from other characterization technique. Asari et al.118 employed STM to investigate a

commercial TiO2 photocatalyst powder (P25, Degussa). The powder was prepared by flame

pyrolysis and consisted of 75% anatase- and 25% rutile-TiO2. They were used as catalysts for

photo-oxidation of organic molecules for chemical syntheses and pollution abatement. They

showed that the TiO2 crystallites came in myriad of shapes and sizes, and displayed stepped

surfaces populated with point defects. They demonstrated that one could identify the phase

structure of the TiO2 crystallite (i.e., anatase and rutile) by measuring the intervals of atomic

rows on the surface of the crystallites. Yeung and coworkers 217-223 described the preparation

nanostructured TiO2 crystal with well-defined crystal and aggregate size and shape using a

modified sol-gel method. The amorphous titanium oxide gel spheres of uniform size and shape

were precipitated from a titanium alkoxide solution. TiO2 crystallites of well-defined size, phase

structure and surface chemistry were crystallized using either a thermal or hydrothermal process.

Atomic force microscopy, transmission electron microscopy, X-ray diffraction and absorption

spectroscopy and Raman microscopy were used to characterize the catalyst structure and

morphology. AFM and TEM experiments showed that the amorphous titanium gel spheres were

completely transformed into aggregate clusters of TiO2 nanocrystals during the crystallization

process. Reaction studies indicated that these nano-TiO2 were very active catalyst for photo-

oxidation of airborne volatile organic pollutants.

Occelli and coworkers224 used an AFM to examine the surface of pillared

montmorillonites. The clay surface appeared as an ordered hexagonal array of bright spots. The

pillaring reaction with Al13 ions consistently led to a larger separation between the

montmorillonite SiO4 layers. The AFM analysis was unable to locate the presence of aluminum

oxide debris or cluster on the surface of silicate layer, which suggested that coking rather than

the formation alumina surface impurities was responsible for the deactivation of the clay catalyst.

Yamamoto et al.206 were the first to employ an AFM to study the surface morphology and

structure of KMn8O16 powder catalyst, which was a working catalyst for the oxidation or

hydration of nitriles to amides. They used the bulk structural data to confirm the needle-like

crystallite morphology and faceted surface structure imaged by AFM. The facets exhibited

regular hill-and-valley topography with a height difference of 0.2-0.3 nm along the long axis

(i.e., c-axis) of the crystallites. They deduced that the surface of the hills had (110) orientation

and the valleys were formed by the removal of O-Mn-O units from the (110) surface. They

further claimed that the periodic structure of the hills corresponded to the configuration of

surface hydroxyl species and bridging oxygen atoms of the (110) plane. They also suggested that

the surface hydroxyl had to lie slightly above the bridging oxygen atoms, which could better

explain the hydration mechanism on this catalyst.

Sol-gel synthesis is an important catalyst preparation method and the structural evolution

during the sol-gel process is an influential factor that determines the final properties of the metal

oxide catalyst. This phenomenon has been investigated at different length and time scales using

various spectroscopic techniques. NMR spectroscopy and chromatographic technique are useful

for identifying the different oligomeric species formed by the hydrolysis, condensation and

polymerization reactions during the early stages of gelation. Infrared and Raman spectroscopies

provide important information on the growth and structure of local inorganic frameworks, and

small-angle-scattering methods using X-rays (SAXS) and visible light give insights into the

formation, growth and topology of colloidal sols and macromolecular gel networks. However,

most of the information on the local structural environment (i.e., 1-100 nm) is deduced from

indirect measurements using photophysical and photochemical probe molecules. Through

quenching method, electron microscopy has provided high magnification snapshot pictures of the

phenomenon, but due to the sensitive nature of sol-gel material this is not often used. In-situ

AFM is a perfect technique for noninvasive monitoring of the genesis and growth of the catalyst

structure during the sol-gel process. A recent work by the author and G.X. Xiong’s group from

the State Key Laboratory of Catalysis at Dalian Institute of Chemical Physics demonstrates the

use of in-situ AFM for the study of sol-gel synthesis of mesoporous aluminosilicate catalysts.

Figures 4a-4c display the optical micrographs showing the formation and growth of

silica-alumina gel networks prepared by sol-gel method under acidic conditions. The formation

of fractal structure was rapid with an inception time of less than 15 s and was complete within 2

minutes. The open, randomly branched structure shown in the figures is a characteristic of

reaction-and/or diffusion-limited cluster-cluster aggregation (RLCA or DLCA) that is expected

to occur under low pH and in the absence of monomer. The fractal structures formed from acid-

catalyzed growth were kinetically stabilized since the absence of monomer specie prevented

further restructuring. However, this does not mean that the internal structure of the branches was

static as shown in Figs. 4d-4i. It is clear from Fig. 4d that the silica-alumina branched structures

are made of aggregated nanometer sized clusters that have an average size of 120 nm. Although

the gross structure remained unchanged (Figs. 4d-4i), the clusters had coarsened and grown in

size during the 720 minutes of observation. The average size of the clusters was about 1.6 µm at

the end of the observation. Two growth mechanisms can be identified from the figures. Groups

of two to six clusters were observed to agglomerate and form larger grains (see label A & B), but

individual clusters were also seen to grow slowly with time through Ostwald ripening process,

whereby the dissolution of smaller clusters fueled the growth of the larger particles (see label C

& D).

The clusters located along the edges grew preferentially due to their higher surface free

energy and more reactive properties (i.e., acidity). Clusters labeled E and F were observed to

grow through agglomeration of smaller clusters and ripening processes, respectively. The genesis

of these clusters can be clearly seen in the figures. Unlike the clusters A to D, they were unstable

and were eventually re-absorbed into the primary structure or re-dissolved into the synthesis

solution. This observation confirmed that although unlikely, depolymerization and dissolution of

clusters did occur at low pH and were possible source of dilute concentration of monomer and

oligomer species. It was highly probable that the dissolved species were rapidly recaptured

within the immediate vicinity of the dissolving clusters, and were therefore difficult to detect in

the liquid phase of the synthesis mixture. Movement and migration of the clusters and aggregates

were also evident (label G & H). These movements were small, mostly in the order of tens of

nanometer and were related to the internal restructuring of the gel network and the relatively

weak bond that held the gel structure to the underlying mica substrate. Since the nanometer-sized

clusters and their packing arrangement dictated the pore size of the silica-alumina catalyst, the

ageing of the gel was therefore a critical factor in the preparation of these materials. The study

showed that although the gross structure of the gel network was static, there was an active

internal restructuring of the constituent clusters through sintering, growth and migration. A better

understanding of these dynamic processes would enable the rational design of sol-gel materials.

1.2. Supported Catalysts

Practical catalysts usually consist of high surface area metal and metal oxide clusters

stabilized on a support material. Carbons and refractory metal oxides such as silica, alumina and

titania are the most common catalyst support because of their large surface area, high thermal

stability and good corrosion resistance. Most industrial and laboratory catalysts are prepared by

wet chemistry (e.g., co-precipitation, impregnation and ion-exchange) on powder support and

possess complex structure and morphology that are difficult to image and interpret. But with care

and effort, one can occasionally succeed in imaging real catalyst surface. Figure 5 is a platinum

catalyst supported on graphite prepared from tetraamine platinum nitrate solution by wet

impregnation, followed by a high temperature treatment in hydrogen at 723 K for 60 h. The

catalyst was dispersed in water by sonication and after quiescence; a thin continuous graphite

layer was formed at the air-water interface. The catalyst was transferred onto a highly oriented

pyrolytic graphite single crystal and imaged using STM. Figure 5 shows that the reduced

platinum particles are cubic in shape but with a truncated height. The surface of the particles is

rough and higher magnification image revealed a faceted surface populated with steps, kinks and

defects. Atomic resolution images showed that the majority of the surface facets display (100)

atomic arrangement as shown in the figure. Defect structures such as kinks, adatoms and missing

surface atoms are common and may play a significant role in the catalyst activity. The high-

resolution image of the graphite bond structure in Fig. 5 is possible only because of the high

density of defects in the powder graphite support. The Pt/graphite catalyst was active for low

temperature 1,2-butadiene hydrogenation at 323 K.

Model supported catalysts prepared by gas phase deposition techniques (e.g., sputtering,

evaporation and electron-beam deposition) on well-defined single crystal surfaces were used in

most of the SPM studies to obtain a basic molecular-level understanding of the mechanism of

heterogeneous catalysis. Ultrafine gold supported on titania is one good example. This catalyst

had been shown to be reactive for low-temperature CO oxidation, 225-227 propylene epoxidation

228-230 and nitrogen oxide reduction.231 It had been shown that size of the Au particles played an

important role in these reactions with 2-4 nm particles having the best catalytic performance.228

Mitchell et al.151 used an in-situ STM to monitor the dynamic behavior of Au nanoparticles

deposited onto TiO2 (110) single crystal support under UHV. Gold evaporated onto the support

grew in discrete islands with a mean diameter of 2 nm at low surface coverage of 0.02 monolayer

(ML) and 5 nm at 0.7 ML. Gold clusters smaller than 5 nm were extremely mobile and diffused

on the TiO2 along the general <001> direction, but the larger gold particles were immobile.

Cluster nucleation, coalescence and growth were observed when the samples were annealed at

750 K. The dominant growth mechanism was still by gold atoms transported across the terraces.

At 873 K, gold evaporation competed with the ripening process. Goodman and coworkers232 also

showed that gold clusters smaller than 4 nm were unstable and sinter at temperatures of about

450 K and oxygen pressures greater than 10-1 torr. They reported that the interaction between the

deposited gold clusters and titania support was significantly weakened at oxygen pressure higher

than 10-4 torr. Indeed, Sykes and coworkers233 observed that gold deposited onto polycrystalline

titania consistently had a larger mean particle size (~20 nm) when exposed to air (Fig. 6a),

compared to the freshly deposited particles (~2.5 nm) imaged by STM in UHV (Fig. 6b). The

exposure to ambient air caused rapid diffusion of Au particles along the grain boundary of titania

resulting in sintering and the process was shown to be driven primarily by oxygen in air, but

water moisture was also suspected to play a role. This demonstrated the need for careful sample

handling and the importance of in-situ observation under controlled environment.

Goodman and coworkers234 investigated the behavior of Au/TiO2 during carbon

monoxide oxidation. The freshly prepared gold catalyst displayed bi-modal particle size

distribution as shown in Fig. 7. Increasing the reactant gas pressure from (1×10-8-665Pa) resulted

in an overall increase in the number of large particles at the expense of the smaller gold particles

that slowly disappear from the surface. Analysis showed that the support was at a reduced

oxidation state indicating that TiO2 was unstable under the reaction condition. Sintering of the

gold particles and changes in the chemical state of the support were possible explanations for the

observed deactivation of Au/TiO2 catalyst. Some recent review articles by Goodman et al.235, 236

summarized the relevant SPM works on Au/TiO2 catalyst. There was a clear relationship

between gold particles size and catalyst activity. The highest CO conversion was obtained at an

optimum particle size of 3 nm. However at elevated oxygen pressure, particle ripening and

formation of volatile gold species led to a loss in activity. The latter resulted in an accelerated

inter-particle atomic transport. The support material was found to have a great influence on the

ripening kinetics of gold particles.

Catalysts prepared by gas phase deposition under well-defined environment have the

advantage of precise control over the catalyst loading and surface coverage, but because of

economic and technical reasons, pratical catalysts are prepared by wet chemistry from solutions

containing the catalyst precursor. Thermal treatments at elevated temperatures under oxidizing or

reducing atmospheres are needed to convert the deposited precursor into active catalyst. SPM

can monitor the deposition of precursor from solution onto the support. Chusuei et al.237 reported

the preparation of Au/TiO2 model catalysts from a phosphine-stabilized hexagold complex.

Fukui et al.238 used Au(PPh3)(NO3) as precursor for nanostructured Au/TiO2 catalysts. The

precursor was decomposed into metallic gold by either calcination or UV irradiation. Figure 8

shows a monotonic increase in gold particle size for calcination temperatures of 313-423 K, but

the gold particle size was smaller when the sample was calcined at 493 K. These catalysts

exhibited poor activity for low temperature CO oxidation. UV irradiation prior to calcinations

was found to be a good method for preparing active gold catalysts with less than 1 nm particle

size.

Biener and coworkers239 investigated the deposition and growth of vanadium on TiO2

(110)-(1×2) crystal. They found that surface coverage and treatment temperature had a

significant effect on the vanadium morphology. Small, isolated vanadium oxides were formed by

dosing the support with small amount of vanadium metal from gas phase or by heat treating a

thin multi-layer vanadium deposited at elevated temperatures (>700 K) under vacuum. The

vanadium was preferentially deposited along the <001> direction of the underlying TiO2 support.

The vanadium cations preferred to bind on the (1×2) oxide added-rows of TiO2 (110) at low

coverage, but as the amount vanadium increased elongated metallic structures were observed.

They observed that the small vanadium islands (i.e., 1-1.5 nm) produced tended to coalesce and

form two-dimensional overlayer with further addition of vanadium.240 For copper deposited on

TiO2 (110)-(1×2), Reddic et al.241 reported that the size of copper particles was invariant with

surface coverage. They observed that increasing the amount of copper deposited resulted mainly

in an increase in the particle population on the surface. Annealing the samples at 700 K produced

larger copper particles (Fig. 9) that displayed approximately similar size (6-7 nm). They differed

mainly in that the particle population increased with copper coverage. These observations

suggested a self-limiting growth mechanism for Cu/TiO2 system. Silver particles displayed the

same self-limiting behavior on TiO2 (110)-(1×1).242 In a separate study, Hotsenpiller et al.243 used

the latent photochemical properties of TiO2 to induce the photochemical reduction and

deposition of silver from an aqueous solution. They reported that the crystal orientation had a

large influence on the quantum yield and rate of the process.

Murray et al.244 investigated the growth of palladium on TiO2 (100)-(1×3) surface.

Atomic resolution of Pd cluster and underlying TiO2 support were obtained at low palladium

coverages (i.e., 0.01 and 0.17 ML). They observed cluster coalescence and formation of large

particles at higher coverage. Annealing Pd/TiO2 (110) at elevated temperature (i.e, 750 K),

Howard et al.245 observed a transition from a unimodal to a bimodal Pt particles size distribution

(Figs. 10a & 10b). A discernable growth in the size of larger Pt particles is evident from Figs.

10c & 10d. This was accompanied by a net shrinkage in the size of the small particles. This

phenomenon was a clear indication that the growth behavior of Pd particles in this system was by

Ostwald ripening process. Gan et al.246 studied Pt supported on anatase TiO2 (001)-(1×4). They

reported the anisotropic diffusion of large platinum clusters from terrace towards the step edge

along an atomic row (Fig. 11) during annealing at high temperature. Dulub et al.247 investigated

the strong metal-support interaction (SMSI) between platinum and TiO2 (110) substrate. Two

types of particle morphologies were observed. Most of the deposited platinum formed elongated

hexagonal shaped particles (type A) aligned along the <001> direction of the substrate (Fig.

12a), but occasionally square-shaped particles (type B) were also observed. Atomic resolution

image of type A particles revealed a surface consisting of zigzag rows of 5-6 atoms along the

close-packed direction separated by triangular areas containing at most ten atoms (Fig. 12b), but

on the other hand, type B particles possessed an amorphous overlayer. The electronic and

geometric structures of the TiO2 substrate surrounding the deposited particles remained

unaffected.

Besides graphite and TiO2, other planar metal oxides have been used as support materials

in SPM studies. Brookshier et al.248 used spin coating method to prepare CuO/SiO2 model

catalyst with narrow particles size distribution. Figure 13 shows that the particle size of copper

increases with increasing concentration of Cu(Ac)2 precursor. Partridge and coworkers249 used a

similar method to prepare Cu/SiO2 from Cu(CH3COO)2·H2O precursor. They used both AFM

and Rutherford backscattering spectroscopy (RBS) to determine the particle size distribution of

copper catalyst. The results indicated that the tip size affected the particle size measurement and

the AFM was only accurate to approximately 50% when compared to RBS for counting

particles. Schild et al.250 prepared VOx/SiO2/Si model catalysts and studied the influence of gas

environment on the catalyst morphology and chemistry using AFM and XPS. Their experimental

results indicated that surface morphology dictate its activity for selective reduction of NO by

NH3.250

Schildenberger et al.251 fabricated various nanostructure on oxidized silicon by using

laser interference lithography followed by metal deposition. The model catalysts were cleaned

and activated through a series of oxidation (i.e., 673 K) and reduction cycles (i.e., 473 K). The

treatment condition did not significantly affect the structure and composition of thick palladium

foil and film (i.e, 500 nm), but XPS binding energy and peak intensity of Pd and Si for a thin Pd

film changed during the treatment. This was attributed to the topographical rearrangement of the

palladium surface. A similar observation was made for nanostructured samples where there is a

loss in surface area due to morphological transformation and sintering of particles within the

nano-dots (7 nm). Unlike the Pd nano-dot sample, silver in the Ag nano-dots spread over the

surface and covered the whole substrate with a grainy layer of small clusters after similar

treatment cycle. This study provided useful insights into “thermal” and “catalytic etching”

effects during catalyst activation cycle.252 The “pitted” nanostructured catalyst was remarkably

stable against “long-range” etching and was tested for CO oxidation where it performed

exceptionally well.251 Recently, the group of Somorjai253 demonstrated the use of electron beam

lithography to prepare supported catalyst array. Pt nanoparticle arrays were deposited onto planar

alumina and AFM was used to test the adhesion between the nanoparticles and support. AFM tip

could easily displace a 28 nm Pt particle with a force of 30 nN prior to heat treatment, but after

annealing in vacuum at 773 K the AFM was unable to move the particle even with a force of

4000 nN. This clearly indicated that heat treatment led to a stronger bond between the catalyst

and support.

Okumura and his colleagues254 prepared Pt, Rh and Pt-Rh alloy catalysts on α-Al2O3 with

<0001> orientation and studied the catalyst growth behavior under oxidizing and reducing

atmospheres using AFM and RBS. 50 to 200 nm platinum crystallites were formed when the

vacuum deposited Pt film was annealed in an oxidizing atmosphere. The Pt crystallites displayed

a characteristic hexagonal shape with (111) orientation. Similar pretreatment had little effect on

Rh film. The addition of Rh to the Pt film inhibited the particle growth under oxidizing

conditions resulting in smaller crystallite sizes, but when the same sample was annealed in a

reducing atmosphere significant particle growth was observed. The average particle size of Pt-

Rh/α-Al2O3 samples was about 100 nm regardless of composition. The study showed that a Rh

concentration of 10 to 50% was sufficient to inhibit the growth of Pt crystallite. This information

is important for developing better formulation and control strategy for three-way catalysts. The

presence of halogen is known to cause a significant loss in metal surface area. Wodiunig et al.

observed the silver particles rapidly sinter in the presence of trace amount of dichloromethane

gas resulting in significant loss in metal surface area. 255

2. Observation of Surface dynamics using Scanning Probe Microscopy

Adsorption, diffusion and reaction are surface processes involved in catalysis. They have

been studied by various spectroscopic techniques that provided essentially macroscopic data on

these molecular events. The invention of SPM enabled the real time imaging of these dynamic

processes at molecular level under different gas environments and conditions. The last decade

has seen a large body of SPM works on adsorption and diffusion, surface reconstruction and

annealing, and catalyst reaction, deactivation and poisoning. These experiments provided

unprecedented information on surface processes that proved invaluable to our understanding of

catalysis.

2.1. Surface Adsorption and Diffusion

Oxygen adsorbed on metal surfaces was the most common adsorbate imaged by SPM.

Oxygen atoms on Ag(110) were mobile even at room temperature and were observed to diffuse

on the surface until collisions led to the formation of Ag-O-Ag chains that propagated along the

<001> direction of the substrate and appeared as added rows of atoms.259-262 The adsorbed

oxygen formed (2√2×√2)R45º overlayer structure on Cu(100),269 but on Cu(110), oxygen

adsorbed as individual atoms on the terraces forming isolated chain structures aligned along the

<001> direction of the crystal surface that culminated in the formation of a (2×1) oxygen

overlayer structure.273-276 The (2×1) oxygen overlayer was transformed into a c(6×2) structure at

high oxygen coverage.273 Oxygen appeared as protrusions on the reconstructed Pt (110) crystal

surface along the ridges of missing atomic rows,287 whereas it formed disordered islands on

Ru(0001) that slowly annealed to produce ordered (2×2) and (2×1) oxygen overlayer structures

at higher temperatures.293 Table 4 provides a list of adsorbates studied by STM and AFM.

Scanning probe microscopy can operate in both UHV and gas environments bridging the

“pressure gap” between the traditional surface sciences conducted at UHV and actual operating

environment of practical catalysts. The group of Somorjai employed a high pressure, high

temperature scanning tunneling microscope (HPHT-STM) to observe the dynamic behavior of

catalytic surfaces from vacuum to atmospheric pressure at temperatures of 300-675 K under both

oxidizing and reducing environments.294 They reported the co-adsorption and competition

between CO and NO on Rh(111) surface. Gas partial pressures comparable to conditions

experienced in a real automobile catalytic converter were used in the experiment. A (2×2)-3(CO-

NO) overlayer structure was formed at low NO concentration. As the surface fraction of NO

increases, NO molecule replaced CO from the hollow sites and proceeded to occupy the adjacent

top sites in the (2×2) lattice resulting in the formation of NO-rich islands.295 NO (3×3) domains

were also present at high NO partial pressure.

Exposure of TiO2 (110)–(1×1) to oxygen atmosphere led to the appearance of additional

surface features such as dots, Ti2O3 rows and (1×1) terraces as the substrate reacted with

oxygen.296 Even at low oxygen pressure (< 2×10-6 mbar) adsorbed oxygen reacted with mobile

interstitial Ti3+ from the bulk material to form individual mobile TiO2 units at temperatures of

573-1000 K. These TiO2 diffused and coalesced into (1×1) and (1×2) domains.216 Suzuki and his

coworkers297 examined hydrogen adsorption on TiO2 (110)-(1×1) surface using STM and

electron stimulated desorption (ESD) techniques. Adsorbed hydrogen atoms formed either

surface hydroxyl or hydride compounds on annealed TiO2 surface. Probe molecules such as

ammonia and pyridine were often used to characterize the acidic properties of the metal oxide

catalysts such as TiO2 and imaging the adsorbed probe molecules could provide a physical

picture of the surface acid sites, their nature, strength and location on the oxide catalyst surface.

Iwasawa et al.298, 299 investigated the adsorption of pyridine and 4-methylpyridine on TiO2 (110)-

(1×1) surface. The pyridine molecules were more strongly adsorbed on the four-fold Ti atoms

located at the edge of the monoatomic steps compared to the five-fold coordinated Ti sites on the

(110) terrace. 4-methylpyridine was adsorbed on TiO2 (110)-(1×1) as an upright chemisorbed

molecule, a flat chemisorbed molecule located at oxygen vacancy sites and a flat physisorbed,

mobile molecule. They have also succeeded in preparing a well ordered structure on a rutile

TiO2(001) surface. This surface is an atomically ordered latticework-like structure that consisted

of wide rows running along the [110] and [1 0] directions with steps and narrow terraces on

their slopes. And it was further proven that this latticework structure was stable to against

thermal reactions of formic acid and methanol.300

Onishi and coworkers301 examined the surface structure of carboxylate-covered (RCOO -)

TiO2 (110) using noncontact-AFM. The van der Waals force was found to be responsible for the

observed molecule-dependent topography. In the presence of formic acid, (2×1)-formate

monolayer is formed on TiO2 surface. The adsorbed formate ions could diffuse across the surface

without disturbing the underlying TiO2 structure. The formate molecules moved along the Ti-

rows with its O-C-O plane parallel to the row.296 Analysis showed that the height difference

between co-adsorbed formate (HCOO-) and propiolate (HC≡CCOO-) molecules on TiO2 (110)-

(1×1) surface was 0.20 nm, which was smaller than the calculated value based on the size of the

free molecules.302 Tanner et al.303 showed that the sticking probability of formate molecules on

the anatase TiO2 (001)-(1×4) surface was initially at unity, but decreased rapidly as the surface

coverage reached 1/8 ML.

The mobility of surface atoms and adsorbates is responsible for many surface-related

phenomena including annealing, surface reconstruction and catalytic reaction. Surface diffusion

has been investigated using different techniques including scanning probe microscopy (i.e.,

STM). Wiesendanger304 described two STM operation modes for investigating surface diffusion.

Rapid diffusion is best studied by monitoring the time-dependent changes in the tunneling

current, while the probe tip is held at a fixed position over the surface. A change in tunneling

current from the baseline value occurs when surface atoms and molecules diffuse underneath the

probe tip. Careful analysis of the data provided valuable information on the diffusion rate and

mechanism.305 Alternatively if the diffusion process is slow, STM can capture the event as it

unfolds by taking snap-shots of the surface, giving an unprecedented opportunity for observing

each diffusion steps at atomic scale resolution in real time. This had led to new discoveries in

how atoms and molecules move on surfaces.

The most common way by which adsorbed atoms and molecules move on surfaces is by

random hopping from site-to-site. On metallic surfaces, adsorbates are bound to the surface by

metallic bond, whereas on semiconductor surfaces, they are held by highly directional, covalent

bonds that can severely restrict the freedom of their movement.306 The adsorption and diffusion

of adsorbed hydrogen atoms on Si(111)-(7×7) was investigated using STM by Lo and

coworkers.307 They observed that hydrogen atoms hopped between neighboring silicon rest

atoms (R) via a metastable intermediate adatom state (A). Figure 14 shows the filled-state STM

images of two Si(111)-(7×7) surfaces after hydrogen exposure. Normally, the hydrogen atom

adsorbs on top of a rest atom site (R) and the point defect created by the hydrogen adsorption is

invisible, but as consequence the surrounding adatoms (A) appear brighter in the STM image. At

low temperatures (613 K), the movement of the hydrogen atom was restricted to within a

Si(111)-(7x7) half-cell (Figs. 14a & 14b) and only at higher temperatures could hydrogen cross

the half-cell boundary (Figs. 14c & 14d). The motion of adorbed oxygen molecules on the

Si(111)-(7×7) surface was described by a molecular tumbling model.306, 308 Small and weakly

adsorbed atoms can move across the surface by tunneling process instead of the usually

thermally activated random hopping.306 STM was also instrumental in identifying a third

diffusion process, wherein an adsorbate moved by displacing a substrate atom. This diffusion

process is believed to be energetically more favorable compared to hopping across a bridge site,

where all the atoms involved in the jump process must necessarily maintain a high coordination

number. This diffusion process is observed primarily in reconstruction of surfaces that display

metastable structure.306

SPM has been used to measure the mobility of adatoms and clusters on different surfaces.

The self-diffusion of silicon adatoms on Si crystal surfaces was among the most studied

system.309, 310 Linderoth et al. 311 reported the one-dimensional diffusion of Pt adatoms on the

Pt(110)-(1×2) surface. They showed that Pt adatoms could jump not only to the nearest

neighboring sites but could also skip to the next nearest neighbor sites during self-diffusion.

Cluster diffusion is known to play an important role in film growth and particle sintering.312

Recently, Wen et al.313 showed that large Ag clusters containing 100-720 Ag atoms could diffuse

across the surface of Ag(100). The diffusion process was best described by a 2D evaporation-

condensation mechanism.313 Tsong and coworkers314 reported the diffusion behavior of silicon

“magic” clusters on Si(111)-(7×7). These clusters were stable not only with respect to surface

diffusion, but also to step fluctuations and epitaxial growth. Although the movement of Si magic

cluster is usually confined within a half-cell of Si(111)-(7×7) as shown in Fig. 15, it can on

occasion make long-distance hops across the surface (Fig. 16). Using an immobile defect

(marked O in Fig. 16) as a landmark, the movement of a magic cluster was tracked from the

upper-left corner of the picture in Fig. 16a to lower portion of Fig. 16b in the general direction of

the heating current. A second magic cluster was observed to move in the same direction as the

first cluster (cf. Figs. 16c-16e).315 It was determined from these studies that the magic clusters

played a critical role in many surface processes that occurred on Si(111) surfaces including step

fluctuations and epitaxial growth.315, 316

Surfaces are populated mostly by terraces, steps and kinks with the occasional adatoms

and defects. Steps and kinks are believed to be the primarily vehicle by which a crystal surface

can rearrange. STM studies showed that even at room temperature the step structure of some

metal surface like gold, silver and copper could undergo rapid changes.304 On stepped copper and

silver surfaces, it was observed that the high mobility of the kink sites was due to the rapid

ejection and capture of adatoms diffusing along the step edges.317, 318 Kuipers et al.319 employed a

high-speed, high temperature STM to investigate the dynamic behavior of monoatomic steps on

Au(110) from room temperature to 590 K. Within the temperature range of their study, they

observed that fluctuation in the step structure was caused mainly by diffusion of kinks along the

step. They confirmed that the migration of kinks occurred through direct exchange of atoms

between the kink and adatom sites on adjacent terraces. The mean-square displacement of the

step was shown to be dependent on the kink density and time. Gimzewski et al.320-322 reported the

temporal evolution of the step structure on a Au(110)-(1×2) reconstructed surface. They found

that the kink sites on the reconstructed gold surface were as mobile as on non-reconstructed gold.

In addition, the kink sites appeared to be critical for the nucleation and growth of the (1×2)

phase.

Surface vacancies are shown to play a role in atom transport on surfaces. Frenken and

coworkers323-325 embedded small concentration of indium atoms within the first layer of Cu(001)

as tracers to monitor the movements of surface atoms. They found that the indium atoms were

mobile and could hop over distances larger than one lattice spacing. Some indium atoms were

able to hop as far as five lattice spacing as shown in Fig. 17. They concluded that small amounts

of extremely mobile surface vacancies were responsible for the diffusion of indium atoms. This

means that even at room temperature one cannot assume that surface terraces are static.

Morgenstern et al.326 investigated the movements of vacancy islands on Ag(111) crystal surface.

The single-atom deep, 2-dimensional vacancies were observed to perform a random walk across

the surface. Measuring the diffusion coefficients of vacancy islands as a function of their size, a

new microscopic mechanism for mass transport was described by the group, where the diffusing

adatoms cut across the vacancy island instead of moving around the perimeter.

2.2. Surface Reaction

There are many characterization techniques capable of monitoring surface reactions such

as infrared-visible sum frequency generation (SFG)-vibrational spectroscopy and photoemission

electron microscopy (PEEM) that had been successfully used to study ethylene hydrogenation on

Pt(111) and CO adsorption on oxygen-saturated Ag deposited on Pt(110).327, 328 But none

possesses the unique ability of SPM to observe these processes at atomic level and in real time.

Scanning tunneling microscopy is responsible for revealing the detailed mechanistic steps of

several catalyzed surface reactions. A detailed review of surface reactions on metal surfaces

studied by STM are given in articles written by Murray et al.,329 Leibsle et al.,330 Ertl331 and

Atamny et al.332 The simplest reaction studied by STM is the recombinative desorption of

hydrogen from Si(001) surface. Dürr et al.333 reported that the desorbed hydrogen molecules

were formed from neighboring silicon dimers. Teague et al.334 used STM to examine the reaction

of 1,3-Cyclohexadiene on Si(100)-2×1 surface. In addition to the intradimer [2+2] and [2+4]

products, another two different [2+2] conformers were identified. Wintterlin et al.335 successfully

used the STM to identify the active sites for the dissociation of NO molecules on Ru(0001). The

NO was observed to dissociate into atomic nitrogen and oxygen along the step edge. They

reported two types of step sites (i.e., step I & II). Step I suffered from self-poisoning and could

only dissociate a limited number of NO molecules. Wintterlin et al.336 also investigated the

catalytic oxidation of hydrogen on Pt(111) surface using STM. High-resolution images revealed

that the pre-adsorbed oxygen atoms formed an ordered (2×2) overlayer on the Pt surface.

Hydroxyl (OH) islands appeared when the oxygen layer was exposed to hydrogen. These islands

expanded rapidly into the oxygen-covered surface during the reaction, forming a ring-shaped

reaction front as shown in Fig. 18. The front displayed both uniform velocity and width that are

characteristics of propagating fronts observed in most autocatalytic reaction-diffusion systems.

The OH islands were shown to transform into islands of adsorbed water as the reaction

progressed. The same reaction was also studied on Pd(111) by STM. The observation indicates

that the Pd step edges are the main reaction site and the formation of OH group at these sites

dictates the overall reaction rate.337

Wintterlin and coworkers338 investigated the catalytic oxidation of carbon monoxide on

Pt(111). They observed a similar (2×2) overlayer structure upon chemisorption of oxygen on

Pt(111). The oxygen atoms within the chemisorbed overlayer were less mobile after the addition

of carbon monoxide. The appearance of a c(4×2) ordered structure was attributed to adsorbed

CO. As time progressed, the area occupied by c(4×2) CO overlayer grew at the expense of the

(2×2) oxygen overlayer until the reaction was completed (Fig. 19). The STM images show that

the reaction did not take place randomly, but occurred mainly along the boundary between the

oxygen and carbon monoxide domains on Pt(111) surface. A quantitative analysis of the STM

data provided an atomic level description of the chemical reaction kinetics that was in good

agreement with the macroscopic measurements. Hendriksen and coworkers339 investigated CO-

oxidation reaction on Pt(110) using a specially designed high temperature and high pressure

STM reactor cell. The flow reactor was connected to an on-line mass spectrometer for analysis of

the reaction composition, while simultaneously observing the surface dynamics using the STM.

The surface was observed to switch reversibly between metallic and oxide states depending on

the gas pressure, and the formation of the surface oxide had a dramatic effect on CO2 production

rate. The study also revealed several new surface structures that were absent at low-pressure

experiments and were only observed in the presence of reaction gases.

Over’s group340, 341 also conducted the same reaction on RuO2 (110) surface. Data from

STM, low energy electron diffraction (LEED) and density functional theory (DFT) calculations

indicated that the coordinatively unsaturated ruthenium atoms (cus) of RuO2 (110) were the

active sites for the reaction. The Ru (cus) atoms in RuO2 (110) were bare and were not capped by

an oxygen atom. On RuO2 (110) surface, the CO molecule sat on Ru (cus) and combined with

the bridging oxygen atom to produce carbon dioxide. The ruthenium atoms were observed to

agglomerate with the depletion of bridging oxygen. The agglomeration was rarely observed

under steady-state reaction condition, since the consumed lattice-oxygen could be replenished by

oxygen uptake from the gas phase. Nakagoem and his colleagues observed the clean-off reaction

of O adatoms by CO on Ag(110)-(2×1)-O surface. At low oxygen coverage, the reaction appears

to be faster along the fluctuating AgO chains, clearly demonstrating the effect of heat-induced

structural fructuation on the reaction rate.342 Leibsle and coworkers 343-345 reported the reaction

between methanol and pre-adsorbed oxygen on Cu(110). At room temperature, they observed the

removal of oxygen islands and the formation of methoxy-induced ‘zig-zag’ features alongside

the remaining (2×1) O islands. Large islands of (5×2)-methoxy unit cell were established after

prolonged exposure to methanol. The size of the islands shrank as the adsorbed methoxy

decomposed into formaldehyde and hydrogen. The decomposition occurred mainly along the

island edges. The authors346, 347 also studied the reaction between formic acid and adsorbed

oxygen on Cu(110). They found that the reaction occurred in one-dimension along the Cu-O

rows of the (2×1) O island producing surface formates. Scheibe et al.348 employed STM and

LEED to image the NH3 + O2 reaction on Pt(533) surface at low pressure (10-7-10-3 mbar). They

reported that reaction-induced surface reconstruction and high mobility of Pt atom led to

structural transformation and resulted in a significant change in reaction selectivity.

Besides passive observation of surface processes and dynamics, Somorjai and his

coworkers349 demonstrated that STM probe tip could participate and even mediate surface

reactions. In their experiments, carbonaceous fragments deposited onto Pt(111) were

rehydrogenated using a catalytic STM tip (Pt(80%)-Rh(20%)) in a reactor cell filled with either

pure hydrogen or a mixture containing 10% propylene in hydrogen. Reactor pressures of up to 1

atmosphere were used in the experiment. The carbonaceous deposit was selectively removed

from the surface with a nanometer spatial resolution. The effectiveness of the catalytic tip

decreased with time due to the deposition of surface contaminants. The same catalytic tip could

also catalyze the oxidation of the carbonaceous fragments.350 In these experiments, the gases in

the reactor cell were replaced with oxygen. It was observed that the tip lasted longer under an

oxidizing environment. The platinum tip could not catalyze the reaction when the hydrogen and

oxygen pressures were less than 0.5 and 5×10-3 Torr, respectively.351 On the other hand, gold tips

were inactive for the removal of carbonaceous deposit in either reducing or oxidizing

atmospheres. They proposed that the catalytic tip served as a source of reactive hydrogen and

oxygen atoms (Fig. 20). These atoms were transferred to the carbonaceous fragments when the

tip was brought into their proximity resulting in their hydrogenation or oxidation.

2.3. Coke deposition and poisoning

During hydrocarbon conversions, organic molecules can decompose and deposit on the

catalyst surface forming a carbonaceous coke deposit. Coking causes catalyst deactivation and it

is therefore important to understand the coke formation process during catalysis. Land et al.352

reported the deposition of nanometer-sized carbonaceous particles during the dehydrogenation of

acetylene on Pt(111) at ultrahigh vacuum. Somorjai’s group353 investigated the effects of coking

on the surface structure of Pt(111) catalyst surface. The coke was deposited by propylene

decomposition under different gas environments (i.e., vacuum, propylene/hydrogen and carbon

monoxide) at reaction temperatures of 300-800 K. The average step structure of the Pt(111)

surface remained unchanged under reaction conditions in a gas mixture containing 10%

propylene in hydrogen (~1 atm). The carbonaceous deposits formed at 475 K were mobile, but

those formed at 600 K were immobile. The morphology of the carbonaceous deposits was

strongly dependent on the temperature and composition of the ambient gases.353 Gaigneaux et

al.354 examined the coke formation on the surface of MoO3-containing catalyst used in selective

oxidation of isobutene to methacrolein. Comparison of the AFM images obtained before and

after reaction helped identify the 10 nm clusters arranged in parallel rows along the <101>

crystal direction as cokes. The size of the coke was smaller on antimony-containing MoO3

compared to coke formed on pure MoO3.

Occelli et al.355 used AFM along with other characterization methods (i.e., N2

porosimetry, microcalorimetry and microactivity testing) to study the effects of coke deposition

on various fluid cracking catalysts used in gas oil cracking. Commercial catalyst containing 20-

30 wt.% HY-type zeolite stabilized by rare earth cations, 50 wt.% Kaolin with the

aluminosilicate gel making up the rest was examined by AFM after their use in gas oil cracking.

3.5 wt.% coke was deposited onto the spent catalyst after reaction. AFM analysis revealed a

surface covered with molecules and chains of molecules, but there was no evidence of coke

deposition that led to pore blockage although the nitrogen sorption experiment showed that 68 %

of coke was deposited within the catalyst pores. In the case of pillared rectorite catalyst, AFM

images of the spent catalyst showed a fairly uniform deposit of coke on the outer surface of the

catalyst resulting in an increase of surface roughness.356 The carbons were preferentially

deposited on or near the three basal oxygen atoms of the SiO4 units that constituted the clay’s

silicate layer. They also investigated the effect of aging and regeneration on the morphology of

fluid cracking catalyst.357 It was found that fresh, spent and regenerated catalysts possessed

similar surface morphologies. The main distinguishing feature of the spent FCC surface was the

presence of regions containing surface debris that disappeared after regeneration.

Besides deactivation caused by coke, catalysts are vulnerable to poisons. Sulfur-

containing molecules are among the major catalyst poisons and are common impurity found in

fuel and oil-derived feedstock.358, 359 A better understanding of the effects of sulfur on the

structural, chemical and electronic properties of metal and metal oxide surfaces is important for

developing more sulfur-tolerant catalysts. Rodriguez et al.360 gave an excellent review of sulfur

interactions with well-defined metal and metal-oxide surfaces. There was a large body of works

on sulfur-covered palladium surfaces. Adsorbed sulfurs form different overlayer structures on Pd

including (√3×√3)R30° and (√7×√7)R19.1°.361-364 STM studies showed that (√3×√3)R30° S

overlayer on Pd(111) coexisted with the (√7×√7)R19.1°, disordered and (2×2) sulfur domains.364

Speller et al.365 reported that for (√7×√7)R19.1° sulfur overlayer on Pd(111), the sulfurs were

adsorbed on the fcc and hcp sites of Pd. Bürgler et al.366 studied the dynamic behavior of sulfur

layer on the Pd(001) surface. They observed the formation of c(2×2) S-overlayer and a variety of

defect structures including steps, vacancies and anti-phase domain boundaries on the surface.

Zaera et al.367 conducted STM and LEED experiments on co-adsorption of S and CO on

stepped Pt(111) surface. Exposure of Pt surface to sulfur led to the formation of p(2×2) sulfur

overlayer and the slow doubling of the original height as shown in Fig. 21. Subsequent addition

of carbon monoxide reversed the surface reconstruction and induced the formation of 5 nm wide,

CO-covered steps. Exposure of this CO and S covered surface to more carbon monoxide led to

the formation of a complex structure around the steps. Distinct regions of 5 nm wide (2×2) sulfur

structure at the bottom of the step, a narrow CO-covered 2 nm wide intermediate sloped terrace,

and a disordered ledge were found around the steps. The reaction of sulfur dioxide with pre-

adsorbed oxygen on Ag(110) was studied by Alemozafar et al..368 The reaction of SO2 with the

p(2×1)-O oxygen overlayer at 300 K produced a surface covered by sulfite with a c(6×2)

arrangement with six sulfite species in a unit cell. When the temperature increased to 500K, the

sulfite disproportionated to SO2(g), SO3(a) and subsurface oxygen. This resulted in the formation

of p(1×1) structure, which contained irregular rows of c(3×2) unit cells aligned 22° from the

<001> direction. Heating to a higher temperature (i.e., 600 K) resulted in the desorption of SO3(a)

leaving a sulfate-covered surface that displayed a p(3×2) structure, with one sulfate moiety per

unit cell. Recently, the disproportionation of SO2(g) into sulfur and sulfite on Cu(110) and

Cu(110)-p(2x1)-O was investigated with STM. Surface pitting and incorporation of a

stoichiometric quantity of Cu into the sulfite structure was found on Cu(110). On the Cu(110)-

p(2×1)-O surface, SO2(g) tend to react with an equal amount of Cu-O producing a Cu(110)

surface covered with an equal number of SO3 moieties and copper atoms overlayer.369

Rousset et al.370 studied the adsorbate-induced, two-dimensional faceting of steps on

S/Cu(1111) surface. At 0.25 coverage, two different superstructures of sulfur defined by p(2×2)

and c(4×2) symmetries coexisted on the stepped surface of Cu(1111). The orientation of the

steps was strongly correlated to the superstructure present on the adjacent terraces. Ruan et al.371,

372 investigated the structure of S/Cu(111) surface at different sulfur coverage. The and

(√7×√7)R19° surface structures were formed respectively at low and high S coverages. It was

observed that Cu atoms along the step edges were consumed to form during the (√7×√7)R19°

reconstruction of terraces.371 For the S/Ni(111) system, the individual S atoms produced by

decomposition of H2S appeared as protrusions with a height of 0.3-0.4 Å and formed a local

p(2×2) structure near the step edges. The surface underwent a reconstruction to a (5√3×2)

structure after further exposure to H2S. The reconstruction was accompanied by a homogeneous

nucleation of small islands created by the ejection of Ni atoms from the terrace.372 Sulfur

overlayer structure on Fe(110) surface underwent c(6×4), (3×1) and (1×1) reconstructions

depending on the surface coverage (i.e., 0 to 1 monolayer).373 In excess of a monolayer

coverage, a (2×1) superstructure was formed on top of the Fe(110)(1×1)–S structure. Higher

sulfur coverage led to the formation of zigzag structured that ran from the step edge across the

terrace. The zigzag rows were oriented along <1ī1> and <001> directions, and formed a quasi-

ordered parallelogram structure.

The effects of sulfur on oxide surfaces were investigated by the groups of Hartmann 374

and Hebenstreit. 375, 376 Hartmann et al.374 reported the effects of sulfur dioxide on TiO2 (110). In-

situ STM observation showed that the addition of SO2 coincided with the appearance of new

random clusters on the rows of (1×2) reconstructed TiO2 (110) domains on the surface. Higher

exposure led to the formation of ordered adsorbate overlayer with a (2×1) structure that sat on

top of the rows of fivefold coordinated titanium cations found on (1×1) TiO2 (110) domains.

Hebenstreit and coworkers375, 376 found that the sample preparation temperature had a strong

influence on the adsorption of elemental sulfur on TiO2(110) surface. They also observed that the

preferential adsorption of sulfur on the rows of fivefold coordinated titanium atoms on TiO2(110)

surface. At 573 K, the sulfur atoms tended to adsorb on the rows of bridging oxygen instead of

titanium atoms forming short chain-structure along the <1ī0> direction at low coverage. At high

coverage, the overlayer formed a (3×1) superstructure. In their work, the sulfur atom preferred to

substitute for every third bridging oxygen atom of the titanium dioxide substrate. The other

bridging oxygen atoms were completely removed during this process.

Halogens are the other common class of catalyst poisons. Their presence leads to the

formation of inactive halides and in some cases to etching and loss of catalyst materials. Etching

by halogens was extensively investigated for Si(100) mainly for their importance in

microfabrication. These studies focus on the morphologies of the silicon surface produced by

high temperature etching with halogen gases. Chander et al.377 reported the reaction pathway and

energy anisotropies of chlorine etching of Si(100)-(2×1) surface. The halogen molecules were

shown to adsorb dissociatively at the dangling bonds of silicon surface378 and the formation of

surface vacancies was considered to be an important step in silicon etching.379 The adsorption of

halogen on metal surfaces had been well studied by STM.380, 381 The formation of ordered halide

adlayers on gold single crystals had been reported for Au(111),382-388 Au(100)389 and Au(110).389

Cuesta et al.390 also investigated chlorine and bromine adsorption on Au(100) electrodes. Endo et

al.391 showed in their study that bromine adsorbed on Ag(111) formed an ordered hexagonal

(3×3) overlayer structure instead of a (√3×√3)R30°. Addition of cadmium led to the formation of

a tighter close-packed hexagonal overlayer structure with distance of 3.9Å.

Nakakura et al.392-394 and Andryushechkin et al.395, 396 investigated the adsorption of

halogens (i.e., Cl, Br and I) on Cu(100) and Cu(111). Nakakura’s group observed that the

chemisorption of Cl2 was indistinguishable from that of Br2. Both halogen molecules formed

c(2×2) adsorbate overlayer on Cu(100) at trace amounts, but near saturation (i.e. ∼70%) the

overlayer structure could not be easily imaged by STM due to the high mobility of the halogen

adatoms. Faceting of the steps along the <100> direction was observed for chlorine as well as

bromine on Cu(100) close to saturation. The steps remained the main source of copper atoms for

the formation of copper halides. It was discovered that surface defects such as kinks and domain

boundaries did not play any role in the reactivity of the faceted steps for halide formation. The

reactivity of the steps was nonuniform, and was strongly dependent on the treatment conditions.

Annealing at high temperature made the surface less susceptible to halide formation and more

tolerant of the halogen poisons.392-394 Iodine on Cu(111) formed a (√3×√3)R30° adsorbate layer

with one iodine atom per unit mesh at a coverage of less than 0.33 monolayer. A uniaxial

compression of the chemisorbed iodine layer was observed at surface coverage between 0.33 and

0.38 monolayer. Above saturation, copper iodide islands started to form from the chemisorbed

iodine.395 Adsorption of iodine on Cu(100) displayed the p(2×2), disordered (liquid), c(6×2),

c(14×2) and c(5×2) phase structures depending on the surface coverage (Fig. 22). Simple first-

order phase transition theory can explain the transformation from p(2×2) to disordered liquid and

finally to c(6×2) phase structure. It also perfectly described the transition from c(6×2) to c(14×2),

but the phase transformation from c(14×2) to c(5×2) was related to a second-order phase

transition.396

3. Nanomanipulation using Scanning Probe Microscopes

Since the early days of its discovery, scientists have realized that scanning tunneling

microscope offers an unprecedented opportunity for nanoscale manipulation of atoms and

molecules on surfaces. The close proximity of the probe to the surface and the precise control

over its movements enable the use of probe tip to sculpt the surface to create both mundane

features such as pictures and logos or advanced nano-devices and nano-circuitry. The probe can

exert enormous electrical and magnetic fields as well as mechanical pressure on localized

regions of the surface, and thus altering at nanometer-scale the local physical, chemical,

electrical and magnetic properties of the material. Molecules and clusters can be moved and

positioned on surfaces using STM and AFM as nano-tweezers. The probe tip can even guide and

direct surface phenomena such as adsorption, diffusion and reaction at atomic and molecular

levels. This clearly demonstrates the potential use of scanning probe microscopes as nano-

assembler for building complex molecular machines from atoms and molecules.

3.1. Mechanical Patterning

Surface patterning at nanometer-scale using scanning probe-based lithographic (SPL)

method397 has attracted the interest of researchers in both physical and engineering sciences. It

opened a new opportunity for creating complex atomic and molecular-scale surface architectures.

One simple and direct SPL method used the probe tip to mechanically displace materials on the

surface to create dents and grooves as shown in Fig. 23a. About a decade ago, Loenen and

coworkers398 showed that the nanometer-sized surface indentations on Si(110) and Si(001)

created by UHV-STM were made purely by mechanical displacement of silicon atoms rather

than the current-induced local melting of the surface. Soft, malleable metals such as gold, silver

and nickel were easily patterned by this method using either STM or AFM. Both thin films and

single crystals had been employed in these studies 399-406 and had been discussed in detail in an

excellent review by Nyffenegger and coworkers. 407 One such study used the grooves made on

gold surface to study the surface diffusion of gold atoms during the annealing process. The

gradual disappearance of the groove with time was captured in a series of STM pictures.

Atomic force microscope is more widely used for mechanical patterning of surfaces,

since the force applied by the tip can be precisely adjusted to give the desired indentation. Their

use had been demonstrated on both bare surfaces and surfaces covered with organic layers.408, 409

The AFM tip could directly pattern a surface by mechanical indentation and attrition of the bare

substrate or indirectly by selectively removing attached organic molecules from a photoresist

covered surface followed by an etching process to dissolve the exposed substrate.410, 411 A large

body of works was devoted to patterning of polymer resist materials412-414 with the goal of

advancing this technology for microelectronics and nanoelectronics fabrication. The quality and

resolution of the line patterns drawn using the AFM were dependent on the tip material. Regul et

al.415 compared the line widths drawn by a silicon and diamond tip on GaAs/AlGaAs

heterostructures. A coarser line was scribed using the silicon tip (i.e., 250 nm) compared to the

diamond tip (i.e., 90 nm) using the same force of 50 µN. This was mainly due to the better

hardness property of the diamond tip, which was more resistant to wear. The depletion length of

the diamond-engraved sample was roughly half that of the silicon-patterned device. Instead of a

diamond tip, the probe could be modified and sharpened using electron beam deposition to

improve its mechanical strength and durability.416 These tips had been successfully employed for

the fabrications of in-plane-gate transistors and single-electron transistors.417 Figure 24 shows

that finer line width and more precise control can be attained by optimizing the operating

parameters of the AFM lithographic method.418-420 Employing cantilever oscillation of contact-

mode AFM, Hyon and coworkers418 had successfully created finer patterns on GaAs with line

widths as narrow as 10 nm and depth of 1 to 4 nm. Using this nanomachining method, Magno et

al.421 had successfully fabricated several III-V semiconductors. They also used selective wet etch

to transfer the feature deeper into the underlying semiconductor material.

It is clear that the current focus and activities in this area is on the design and fabrication

of electronic nanodevices, however the same technology can be readily adopted for catalysis

research. The opportunity to actively participate and guide surface processes and phenomena at a

molecular and atomic-level and the reward from the new knowledge garnered from these

controlled experiments are great. Indeed, some tentative steps in this direction had been taken by

various researchers. One of the earlier reports on surface fabrication using AFM was conducted

on a catalytic material. Patterns were created on thin molybdenum oxide film exposing the

underlying layer of molybdenum sulfide substrate. Precise pattern depth was demonstrated in the

study. 422 Cluster deposition from chemical vapor deposition of InAs on artificially made surface

features (grooves and anti-dots) on GaAs had been investigated by Hyon et al.423 in order to

establish the relationship between deposition kinetics and surface geometry. They observed

preferential growth along edges and within patterned grooves that contained multi-atomic steps.

Microchemical devices such as microreactors and microseparators can benefit from the advances

in STM and AFM-based micromachining methods. To illustrate this, it displays a micron-sized

channel fabricated onto the (002) face of a Sil-1 zeolite crystal using contact-AFM.424 More

recently, it had been shown that the AFM tip could be used to affect the propagation of lamella

structure during the crystallization thin polymer films.425, 426 The force exerted by the probe tip

can disrupt and deflect the propagation of lamella structure as shown in Fig. 25. This is a clear

example of how one can employ the probe tip to manipulate and study complex surface

processes. Besides surface lithography and patterning, AFM tip could be used to slice

multiwalled carbon nanotubes (MWCNTs). 427

Although this SPL method has been successfully employed in nanopatterning and

nanomachining of surfaces, it suffers from several drawbacks. The probe tip can be easily

damaged and worn down during the process leading to unpredictable and uncontrolled variations

in the generated patterns.407 Changes in the probe tip can also affect the microscope’s resolution

and can contribute to image artifacts. Also, probe materials can contaminate the surface and alter

the local composition and chemistry.

3.2. Probe-induced Chemical Modification of Surfaces

Besides using the probe tip to mechanically pattern the surface, the intense electric field

generated by the tip could also melt and modify the local surface. This method had been used to

create small depressions and bumps on the surface of gold and silver by imposing a large

tunneling current and/or voltage between the probe tip and the surface (Fig. 23b). It had been

first postulated that the nanometer bumps were created by a clean metal-metal point contact

between the tip and the surface whereby a strong cohesive bond between the tip and sample

occurred. The subsequent neck formation during the tip retraction subjected the local region

beneath the tip to a large tensile stress resulting in the formation of surface protrusions.

Contaminated probe tips were thought to have poorer adhesion and therefore produced mostly

surface indentations.428, 429 These nanometer scale surface features tended to anneal rapidly,

disappearing in the time scale of minutes to hour. Subsequent works by other authors clearly

demonstrated that local melting of the surface was involved in the formation of these surface

features. Indeed, Hodel et al.430 created line patterns on 20 nm Ag film grown on silicon by using

the electronic field emission from the probe tip to heat, melt and fuse the individual silver grains

into an elongated island (Fig. 26). The same principle had been used to induce local surface

annealing of multi-layered samples consisting of alternating layers of nickel and carbon film.

Alloy formation was suspected to occur under these conditions, although the evidence was

inconclusive. Subjecting the surface to intense electrical field and mechanical pressure, nickel

metal can be preferentially extruded from the composite layer to create nickel droplets on the

surface. This SPL method is usually conducted under inert environment of ultrahigh vacuum or

on inert samples such as gold to prevent chemical transformation of the material during the

lithographic process.

Lebreton et al.431 were able to create stable nanometer-sized holes on Au(111) film using

STM tip. The hole formation was sensitive to the chemical environment. The presence of water

and ethanol vapor favored the formation of holes at positive voltage pulse. The diameter of the

holes depended on the duration of voltage pulses. York et al.432 also used STM to produce

nanometer-sized pits on silver film grown on Cu(100) and selectively modified the segments of

Ag nanowire arrays. Kim and coworkers 433 reported that application of a voltage pulse by STM

Au tip in air could induce Au atoms diffusion on Au (111) surface. Repeated tip scanning

induces fingerlike stripes to grow from stepped surface. The growth direction is correlated to the

local structure of the Au(111) surface and the tip-scan direction. Mamin et al.434 had

demonstrated that tip material could be controllably transferred to the surface. They showed that

gold STM tip could be used as a miniature solid-state emission source for direct deposition of

nanometer-sized gold structures on surfaces. The transfer of tip materials was field-induced and

the authors were able to write a thousand features using this method with no apparent tip

degradation. The patterned gold structures were stable over a period of weeks. Fujita and

coworkers435 used field-assisted atom transferred from a gold-coated tungsten tip to produce

nanoscale gold dots on Si(111)-(7×7) surface under UHV. Using negative voltage pulses, conical

gold dots were formed with base diameter of 3 to 20 nm. The deposition was found to favor step

edges over the flat (111) terraces owing to the higher electrical field at the step edge. Applying

the similar technique (field-induced deposition and diffusion), Houel et al. showed that atoms

can be transferred from the STM tip to the surface to pattern platinum dots and lines on gold or

silicon samples.436

The electric field generated by the tip could also induce molecule hopping and localized

desorption of surface adatoms and adsorbates. Becker et al.437 reported the selective removal of

hydrogen from H-terminated Si(111)-(1×1) surface at room temperature by electron

bombardment (2-10eV) from the STM tip. This resulted in a spontaneous surface reconstruction

from (1×1) structure to a (2×1) π-bonded chain. The desorption of hydrogen occurred with a

promotion of an electron from σ to σ* band. A detailed study conducted by Shen et al.438

reported that the tip-induced desorption on H-terminated Si(100)-(2×1) surface involved two

distinct mechanisms; the direct electronic excitation of Si-H bond by field-emitted electrons and

multiple-vibration excitation caused by tunneling electrons. Stokbro and coworkers439 also

reported on STM tip-induced desorption of hydrogen from Si(100)-H(2×1). Maeda et al. and

Nakayama et al. found that tunneling current and tunneling electron could induce chlorine (Cl)

and bromine (Br) hopping motion on Si(111)-(7×7) and Si(100)-(2×1) surfaces, respectively. 440-

442

Dagata and coworkers443 successfully exploited the enormous electric field generated by

the STM probe tip to induce localized anodic oxidation of single-crystal Si(111) surface from

which emerged another powerful and versatile SPL technology. The process was similar to the

conventional electrochemical anodization, but with the probe tip acting as the cathode and the

ambient moisture serving as the electrolyte (Fig. 23c). Applying a strong electrical field between

the probe tip and the sample surface caused the dissociation of water molecules trapped within

the meniscus formed between the tip and the surface into hydrogen (H+) and hydroxyl (OH-)

radicals. The hydroxyl ions reacted with holes (h+) present on the surface resulting in the local

formation of nanometer-sized oxide dots.444 The consumed water was replenished by an electric

field enhanced condensation process.445 The oxide patterns formed were usually higher than the

surrounding substrates. Its height was found to be linearly dependent on the sample voltage and

it had been argued that the trapping of the free radical ions within the oxide layer was partly

responsible for the prominent surface protrusion.446 The oxidation rate decreased rapidly as the

oxide layer was formed, which was attributed to the effect of self-limiting influence of

decreasing field strengths and the possible buildup of local stress.444 This SPL method had been

successfully used to create oxide patterns on Si,444, 446, 447-450 Nb,451-453 Al,454,455 Ti,456-459 TiN, 460

Zr, 461 metal silicide,462 SiN,463, 464 III-V semiconductor465 and diamond surface.466, 467 The

technique was also used to fabricate masks468-470 for standard lithographic process, but its

greatest potential was for direct fabrication of nanodevices such as single-electron memory units,

single-electron transistors and field-effect transistors.471-486

Both environmental factors (e.g. humidity 487) and STM operating parameters had been

extensively studied to determine their effects on the oxide pattern formation. Silicon was the

most studied substrate because of its obvious application in microelectronics. In their study,

Dagata et al.488 focused on the role of space charge within the oxide layer during the initial stages

of anodic oxidation. It had been shown that the production of O anions was the rate-limiting step

in the anodic oxidation reaction at the early stages. The effects of ion diffusion, space charge and

mechanical stress only became important at the longer exposure times needed to produce a thick

oxide layer.489 Avouris and coworkers444 demonstrated the importance of ambient humidity in

determining the line width of the oxide pattern. Although water was needed to drive the anodic

oxidation, formation of water film on substrate’s surface at high humidity could lead to

defocusing of the electric field, which degraded the lateral resolution of the pattern. Besides

humidity, Marchi et al.490 showed that strong oxidizers such as ozone could promote oxide

formation. They also examined in detail the effects of tip voltage, scan speed, tip-surface

distance on the growth rate of silicon oxide lines on hydrogenated silicon surface. In their study,

oxides were formed only at negative tip biases above a threshold voltage of about – 2V. Indeed,

Teuschler et al.491 found that the field-induced oxidation could only occur when the applied

voltages exceeded a given threshold value that depended on the type and concentration of

dopants in silicon. The quality of the oxide pattern therefore depends on the substrate properties,

tip voltage, tunneling current, scan speed, pulse duration, contact force and ambient humidity. To

better understand the meniscus formation process and the oxidation mechanism, Kuramochi et

al.492 developed a method for monitoring the faradaic current during anodic oxidation. They

claimed that the humidity effects could be ignored, and it is possible to detect minute current

even at high humidity.

More recently, atomic force microscope equipped with conducting probes had also been

used to create nanoscale oxide patterns such as the grids shown in Fig. 27a. Both contact and

non-contact mode AFM had been used. The latter had the advantage of decreasing the wear on

the probe tip and significantly improving the reproducibility and control over the feature size.

Under non-contact mode, the cantilever was vibrated at its resonance frequency at a few

nanometers above the surface. Two operating voltages were used, the initial threshold voltage

was required for the formation of a water bridge between the probe tip and the surface while the

other voltage drove the oxyanions (OH-, O-) towards the interface to generate the oxide layer.493

Detailed study of the local oxide formation suggested that the overall mechanism was similar to

that observed for the STM. Both the width and height of the oxide pattern displayed a

logarithmic dependence on the pulse duration and increased with the applied voltage for a given

pulse duration. Using short pulses at a high voltage (~20 V) gave the highest height-to-width

ratio for a fixed tip-sample distance. It was believed that the short pulses limited the lateral

diffusion of oxyanion species resulting in narrower line width, while high voltage pulses

encouraged the oxide growth.494, 495 Large oxide array consisting of several thousands of oxide

dots with a periodicity of 40 nm and average pattern size of 10 nm had been successfully

fabricated using this method (Fig. 27b).493

The probe tip can also mediate other surface reactions besides oxidation as demonstrated

by Müller et al.496 They employed a platinum-coated AFM tip to catalytically convert the

terminal azide groups of a self-assembled monolayer into amino groups as illustrated in Fig. 28.

The reduction process was achieved in a hydrogen saturated isopropanol solution.496 This

strategy enabled the local chemical patterning of SAM covered surfaces. Palladium coated AFM

tips had been used to catalyze transfer hydrogenation such as reduction of azides to amines,

addition of solvated aminobutyldimethylsilane to terminal carbon-carbon double bond and

hydrogenation of N-benzyloxycarbonyl protected amines in surface assemblies of

organosiloxanes on glass substrates.497 Reduction process could also be achieved by attaching

reducing agents such as sodium triacetoxyborohydride onto the probe tip. Simply scanning the

tip over a monolayer of imines converts them into amines.498 Abruña et al.499 showed that

applying the appropriate voltage to an AFM tip coated with a hydroquinone self-assembled

monolayer, protons could be liberated at will. This modified tip was used to pattern a pH-

sensitive block copolymer at a controlled electrode potential.

The probe tip can also mediate the gas phase deposition of materials onto different

substrates. This was accomplished by dissociating gas phase precursor molecules using the

electron beam emitted by the probe tip. The deposition was localized within the region

underneath the probe tip. Silver and coworkers500 were the first to demonstrate this concept by

depositing cadmium from dimethylcadmium precursor using STM. Similar method had been

successfully employed to dissociate single decaborane molecules. 501 Metallic and semiconductor

patterns were deposited from organometal, SiH4 and WF6 precursors onto different substrate

materials. SiHx spots and islands were deposited and grown onto Si(111) from SiH4 precursor. In

static mode, the size of the semiconductor deposit was controlled by the tip voltage, emission

current and deposition time, but in scanning mode, the raster sped was also a critical parameter.

502

3.3. Dip-pen Nanolithography

A water bridge is normally formed between the probe tip and substrate surface during the

operation of proximal probe microscopes (e.g., STM and AFM) at ambient conditions. “Dip-

pen” nanolithography (DPN) makes use of this water bridge to deliver surface-active molecules

(e.g., surfactants) and precursor materials to the surface (Fig. 29). The tip drags along the water

bridge as it moves across the surface, transferring the “ink” to the surface creating a pattern on

the surface as shown by the schematic diagram. The “ink” molecules are covalently grafted onto

the surface. It is clear that the success of the DPN technique depends on the solubility of the

“ink”, its transport and adsorption onto the surface. The ability of DPN technique for high

precision patterning at the same location using multiple “inks” enabled it to create complex,

nanometer-sized, two-dimensional structural and chemical patterns.503 Early reports used the

AFM tip as a “nanopen” to write on gold surface using thiol-containing organic molecules as

“ink”.503-505 Today, DPN technology had been extended to direct patterning of nearly any

solvable materials including bio-molecules onto surfaces. 506- 514

Ivanisevic and coworkers515 were the first to apply DPN technology for patterning

semiconductor materials (i.e., silicon and GaAs) with organic molecules. Hexamethyldisilazane

(HMDS) was written onto the semiconductor surface. Even with the addition of base to promote

the chemisorption of HMDS molecules, it still required a longer writing time compared to the

patterning of gold surface with thiol-based molecules. This indicated that both diffusion rate and

“sticking coefficient” of the “ink” molecules were the controlling factors that dictated the writing

speed of the DPN lithographic process.515 Thus, increasing the substrate temperature could allow

faster writing speed. Anionic, cationic and neutral dye molecules had been successfully written

onto both bare and chemically modified Si/SiOx surfaces. Unlike most molecules grafted by

DPN, the dye molecules were linked to the substrate by noncovalent interactions. The DPN-

patterned dye molecules were optically active, and this technology is attractive for

manufacturing miniature high precision optical devices.516 Mckendry and his coworkers517

employed dentritic polymers to create nanoscale patterns on silicon surface using DPN

lithograph. Starburst polyamidoamine and polypropylene imine dendrimers were used to create

100 nm wide patterns. They demonstrated that surfaces could be patterned with polymeric

instead of molecular “inks” without significant loss in pattern resolution. Luminescent

nanopatterns of tetramethylrhodamine-tagged human chorionic gonadotropin (HCG) antibody

had been successfully fabricated onto pretreated glass substrates using DPN technique combined

with scanning optical confocal microscopy imaging.518 This technique was particularly useful

where the written patterns cannot be easily imaged by atomic force microscopy.

Inorganic patterns had been obtained by adding inorganic salts to an amphiphilic block

copolymer poly(ethyleneoxide)-b-poly(propyleneoxide)-b-poly(ethyleneoxide) (EO20-PO70EO20,

Pluronic P-123) and using the mixture as “ink” for DPN lithography.519 The P-123 polymer

served to stabilize the inorganic precursor and also lowered the viscosity of the ink. During the

writing process, the inorganic salt was hydrolyzed and deposited onto the surface along with the

P-123 polymer. Thermal treatment removed the organic polymer and left behind a porous metal

oxide pattern. The nanoporous Al2O3, SiO2 and SnO2 had been successfully patterned onto

surfaces.519 The development of electrochemical “dip-pen” nanolithography (E-DPN) by Liu and

coworkers enabled the direct patterning of metal and semiconductor nanostructures on

surfaces.520 The water bridge formed between the probe tip and the substrate act as an

electrochemical cell, where dissolved metal salts could be electrochemically reduced to metal

and deposited onto the surface. Platinum lines of 30 nm width and 0.4 nm height were drawn

using this technique on silicon wafer. An electroless deposition of Au(III) precursor to Au(0)

was demonstrated during DPN of Au onto silicon wafer.521 The authors believed that by

choosing the correct precursor-substrate system, one could use this method to create a variety of

nanostructured patterns. The ability to create high precision metal and metal oxide patterns made

DPN a promising technique for creating catalyst library for combinatorial studies.

Further improvement of the DPN technology requires a better understanding of the

process and the controlling parameters that govern the quality of lithography. Works had been

conducted to investigate the influence of dissolution kinetics, molecular transport and ambient

humidity on the DPN process.522, 523 It had been suggested by many researchers that the

formation of the water bridge is crucial for DPN,524 but the recent successful patterning of 1,16-

mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) on gold in the absence of a

liquid meniscus525 suggested the need for a water bridge was not universal. Several refinements

to the DPN technique had been made over the recent years. One refinement made use of DPN to

create a pattern on the surface using one set of molecular “ink” followed by adsorbing a second

set of molecules onto the rest of the substrate surface.526-529 This technique had been

demonstrated using MHA to pattern gold surface. The remaining exposed surface was then

passivated using ODT. Metal precursors, particles and DNA were then added and selectively

adsorbed onto the carboxylic head group of the MHA molecules to create the magnetic Fe3O4 dot

and line features,526 two-dimensional particle arrays527 and DNA nanopattern528 as shown in the

schematic diagram in Fig. 30. The quality of the pattern was found to depend on the MHA

linewidth and DPN writing speed.526 Amro et al.530 developed a new approach by combining

DPN with nanografting method. This novel method used the tip to displace the adsorbed SAM

molecules from a SAM-coated surface and replaced these molecules with a second type of

molecules from the tip. This technique could be used to produce multi-component patterns with

high spatial resolution. These two techniques were better in preserving the patterns’ geometry

and size compared to conventional DPN technique, since the surrounding matrix molecules

inhibited surface diffusion and prevented pattern smearing. Simultaneous DPN writing and

imaging was achieved by Ali et al.531 using two probe tips, while Zhang and coworkers532

realized parallel DPN patterning by using up to 32 silicon nitride cantilever tips separated by a

distance of 100 µm.

3.4. Nanomanipulation of Atoms, Molecules and Clusters

There is a continuing quest to find ways to manipulate materials at ever decreasing length

scale. Scanning probe microscope’s ability to address and probe individual surface sites makes it

an attractive tool for manipulating individual atoms, molecules and clusters on surfaces with high

precision. Probe mediated manipulation wherein the molecule remained intact involves both

vertical and lateral movements. The lateral movement governs the fundamental nanoengineering

operation of re-positioning molecules and is defined in term of pulling, pushing and sliding

modes between the probe tip and the adsorbed molecule. Pulling and sliding modes involve weak

attractive interactions, where the tip pulls or guides the molecules from one surface adsorbate

site to the next. The molecule precedes the tip and hops along the substrate lattice during the

pushing mode.533 The best known examples of atom manipulation were reported by IBM

research group. Xenon atoms on Ni(110)534 as well as iron and cobalt atoms on Cu(111)535, 536

had been successfully positioned using STM to form logos and words. The atoms were

individually positioned by dragging the adatom using the electrostatic force generated by the

STM tip. The success of moving these atoms depended on the delicate balance of the interacting

forces between the tip, adatom and substrate, and the suppression of thermal diffusion. The

method suffered from the need to operate the process at cryogenic temperature (~ 4 K) under

ultrahigh vacuum conditions, and even the simplest pattern required long fabrication time.

Lyo and Avouris537 used a combination of electrochemical and chemical forces to move

single silicon atoms on Si(111)-(7×7) surface by STM tip. These surface atoms were picked up

by the tip and re-deposited by moving the tip to a predetermined surface location. Uchida et al.538

suggested that the process might involve field-induced evaporation when the experiment was

conducted using voltage pulses above 4 V. This was confirmed by the work of Kobayashi and

coworkers.539 Similar observation was made by Tsong540 for gold atoms on a Au substrate. The

field evaporation could occur at both positive and negative electrical field, but in UHV condition

the STM tip had to be kept at negative polarity. The effect of electrical field was also

examined.541 The work of Kondo et al.542 showed that the needed threshold voltage (Vt) in UHV

displayed a linear dependence on the materials’ binding energy. This suggested that the tunneling

electrons supplied most of the energy needed for local sublimation. The Vt value also displayed

similar dependence once the reaction energy needed for local oxidation was taken into

consideration.

STM has been employed for manipulating adsorbed molecules on surfaces. Lee and

Ho543 used the STM probe tip to transfer and guide the reaction of carbon monoxide molecules

with Fe atoms to form Fe(CO) and Fe(CO)2 compounds at low temperature and under UHV

conditions. A diagram of the process is shown in Fig. 31. During the experiment, the authors

imaged the surface at a low sample bias voltage and tunneling current (i.e., 70 mV, 0.1 nA). A

CO molecule was picked up by positioning the tip over an adsorbed molecule at high bias

voltage and current (i.e., 250 mV, 10 nA) as shown in Fig. 31b. The tip then positioned the CO

molecule over a Fe atom (Fig. 31c). The transfer of CO molecule to the Fe and its subsequent

reaction was achieved by changing the tip bias voltage to –70mV with an increase in the

tunneling current to 10 nA followed by a ramping the voltage to –4 mV (Fig. 31d). The tip-

induced transfer and reaction of adsorbed molecule to the surface provided a real time, direct

visualization of the chemical bond formation between molecules and surface atoms.543 The

reviews of related research area are given in the articles by Ho544 and Hla et al. 545

The manipulation of molecules at room temperature and ambient conditions requires that

the interaction between the adsorbed molecule and the substrate is moderately strong to prevent

random surface diffusion. At the same time, the interaction must not be so strong that it hinders

the controlled movement of the molecule by the tip.546, 547 Therefore, the choice of molecule

must simultaneously satisfy the needs for molecule stabilization and ease of positioning. Cuberes

and coworkers548 demonstrated that C60 molecules could be reversibly re-positioned using STM

tip along Cu(111) monoatomic step at room temperature. Using the atomic steps to restrict the

movement of C60 to one dimension, they constructed a molecular “abacus” using C60 as

computing beads as shown in Fig. 32. Jung et al.547 reported that STM tip could push porphyrin-

based molecules on Cu(100) surface into a stable predefined patterns at room-temperature

without disrupting the internal molecular bonds.

The manipulation of self-assembled monolayers has attracted enormous attention owing

to their potential use as template and resist for nanofabrication.549, 550 The STM and AFM

proximal probes have been successfully used for manipulating SAMs. Several manipulation

methods had been defined including AFM’s nanoshaving and nanografting and STM’s electron

induced molecular diffusion and evaporation (Fig. 33). In nanoshaving, the SAM molecules are

displaced using the AFM tip by applying a high shear force. This technique had been used to

fabricate semiconducting wires using sexithiophene molecules.551 Nanografting was achieved by

conducting the experiment in a solution that contained a surface-reactive molecule. The AFM tip

shaved a pattern from the original SAMs matrix to expose the substrate. The surface-reactant

molecules then adsorbed and bonded onto the freshly exposed surface.552 Nanopatterns

comprising of various thiol-based components on gold surface were fabricated using this

method.553, 554 The advantage of nanografting includes the high precision control over the pattern

size, geometry and location on the surface, and the ability to check and correct the written pattern

in real time. The technique can also be used to grow three-dimensional structures from a two-

dimensional pattern. This is achieved by selecting a surface-reactive molecule that is reactive to

the termini of the SAMs on the patterned area of the surface.555 Multi-layer pattern can be built

using layer-by-layer assembly method based on SAMs technology. Because of these advantages,

nanografting method of surface patterning is now widely used for various applications.556-565

Unlike AFM, the STM tip is not in contact with the surface and modification of SAMs matrix is

achieved by field-induced desorption and evaporation of the SAM molecules.552 The experiment

is usually conducted under UHV condition.

Besides the manipulation of atoms, molecules and SAMs, Brandow et al.566 showed that

catalytically active nanoclusters of Au and Pd could be patterned onto silicon oxide and

functionalized silicon surfaces by physically displacing the nanocluster using an AFM tip. A

similar procedure was used by Schaefer et al.567 to fabricate a two-dimensional array of

nanometer-sized Au clusters on atomically smooth graphite (HOPG) substrate at room

temperature. Junno and coworkers568 employed the AFM tip to position a 50 nm Au particle into

the gap between two Au/Ti electrodes as shown in Fig. 34. They also reported using the AFM tip

to move 30 nm GaAs particles on GaAs surface.569 Lieber and his colleagues570 manipulated

MoO3 crystals to form interlocking nanostructured, while Baumeister et al.571 used the probe tip

to selectively remove SiO2-nanotowers. They detected a very sharp threshold force for fracture

initiation. Park et al572, 573 reported that self-organized Ag nanoclusters on a Sb modified Si(100)

surface could be selectively detached and manipulated at room temperature using STM tip as

nano-tweezers. This could be achieved by either mechanical or field-induced detachment of the

cluster using the STM tip. AFM probes coated with poly(vinyferrocene) redox-active film was

used by Abruña et al.574 as nanotweezers to deliberately manipulate and position sulfonated

chromatography beads on surface. The pick-up and release were accomplished by controlling the

redox state of the ferrocene center by applying the appropriate voltage.

4. Some Closing Remarks

The ability of STM to probe surface electronic states575 and surface chemistry576 has been

demonstrated since the early years of its discovery. Information on electronic structure is

obtained from the voltage dependency of tunneling current during scanning tunneling

spectroscopy (STS). In principle, chemical contrast should be attainable as long as the local

electron density of states (LDOS) of the component atoms are different. Avouris and

coworkers577 were among the first to image the different electronic and chemical states in silicon

surfaces. However, loss in atomic resolution during STS is common, since STM imaging of most

surfaces is obtained within a narrow window of tunnel voltage and current. Although chemical

imaging with STM has meet only limited success, selective imaging of different atomic species

had been reported for different surfaces including GaAs (110)578 and Pt alloys.579 This has been

attributed to an enhanced tip-sample interaction where adsorbed tip impurities such as S and CO

altered the tip’s chemical properties.579 Surface atoms that are more reactive to these adsorbed

species will exhibit stronger interaction with the tip and hence appear higher in the topographic

contrast compared to the other surface atoms. In limited cases, it is also possible to directly probe

the local electron density of states under low noise conditions, but the measured constrast is

usually low. It is conceivable that with the current advances in instrumentation and software, it is

possible in the near future to routinely obtain high resolution SPM topographic as well as

chemical images of surfaces. One plausible design is to use multiple-tip assembly to address the

same surface region. Each tip is selectively coated with a specific functional molecule that has

known interaction with a targeted atom/molecule on the surface. Using image processing

software, one can decipher the chemical information from the different topographic images

obtained by the different tips.

References

1. Binnig, G.; Rohrer, H.; Gerber, Ch.; Weibel, E. Appl. Phys. Lett., 40(2), 178, 1982.

2. Binnig, G.; Quate, C. F.; Gerber, Ch. Phys. Rev. Lett., (56), 930, 1986.

3. Hansma, P. K.; Tersoff, J. J. Appl. Phys. 61, R1, 1987

4. Tersoff J.; Hansma, P. K. Phys. Rev. B 31, 805, 1985

5. Chen, C. J. Introduction to Scanning Tunneling Microscopy, Oxford University Press: New

York, 1993.

6. Doyen, G.; Drakova, D. The physical principles of STM & AFM operation, Vch

Verlagsgesellschaft: Mbh, 2002.

7. Güntherodt, H. J.; Wiesendanger, R. (eds.), Scanning Tunneling Microscopy I: General

Principles and Applications to Clean and Absorbate-covered Surface, 2nd ed., Springer:

Berlin, 1994.

8. Wiesendanger, R.; Güntherodt, H.-J. (eds.), Scanning tunneling microscopy II: Further

applications and related scanning techniques, Springer: Berlin, 1995.

9. Wiesendanger, R.; Güntherodt, H. J. (eds.), Scanning Tunneling Microscopy III. Theory of

STM and Related Scanning Probe Methods, Springer-Verlag: Berlin, 1993.

10. Wiesendanger, R. (ed.), Scanning Probe Microscopy: Analytic Methods, Springer-Verlag:

Berlin, Heidelberg, 1998.

11. Bonnell, D. A., (ed.), Scanning Tunneling Microscopy and Spectroscopy: Theory,

Techniques and Application, VCH: New York, 1993.

12. Sarid, D. Scanning Force Microscopy: With Applications to Electric, Magnetic and Atomic

Forces, revised ed.; Oxford University Press: New York, 1994.

13. Cohen, S. H.; Bray, M. T.; Lightbody, M. L. (eds.), Atomic force microscopy/scanning

tunneling microscopy, Plenum Press: New York, 1994.

14. Cohen, S. H.; Lightbody, M. L. (eds.), Atomic force microscopy/scanning tunneling

microscopy 2, Kluwer Academic/Plenum Publishers: New York, 1997.

15. Cohen, S. H.; Lightbody, M. L. (eds.), Atomic force microscopy/scanning tunneling

microscopy 3, Kluwer Academic/Plenum Publishers: New York, 1999.

16. King, D. A.; Woodruff, D. D. (eds.), The chemical physics of solid surfaces, vol. 8: Growth

and properties of ultrathin epitaxial layers, Elsevier: Amsterdam, 1997.

17. Woodruff, D. D. (ed.), The chemical physics of solid surfaces, vol. 9: Oxide surfaces,

Elsevier: Amsterdam, 2001.

18. Woodruff, D. D. (ed.), The chemical physics of solid surfaces, vol. 10: Surface alloys and

alloy surfaces, Elsevier: Amsterdam, 2002.

19. Jena, B. P.; Horber, J. K. H. (eds.), Atomic force microscopy in cell biology, Academic

Press: San Diego, 2002.

20. Morris, V. J.; Kirby, A. R.; Gunning, A. P. Atomic force microscopy for biologists, Imperial

College Press: London, 1999.

21. Bunshi, Y. STM/SFM of Organic Molecules, Kyoritsu Shuppan Co.: Tokyo, 1993.

22. Kitazawa, K. Science, 271, 313, 1996.

23. Hamers, R. J.; Chen, X.; Frank, E. R.; Higgins, S. R.; Shan, J.; Wang, Y. Isr. J. Chem. 36, 11,

1996.

24. Chiang, S. Chem. Rev., 97, 1083, 1997.

25. Bottomley, L. A. Anal. Chem., 70, 425R, 1998.

26. Bottomley, L. A.; Coury, J. E.; First, P. N. Anal. Chem., 68, 185R, 1996.

27. Poggi, M. A.; Bottomley, L. A.; Lillehei, P. T. Anal. Chem., 74, 2851, 2002.

28. Wintterlin, J.; Wiechers, J.; Gritsch, T.; Hoefer, H.; Behm, R. J. J. Microsc., 152(2), 423,

1988.

29. Wintterlin, J.; Wiechers, J.; Brune, H.; Gritsch, T.; Hoefer, H.; Behm, R. J. Phys. Rev. Lett.,

62(1), 59, 1989.

30. Doyen, G.; Drakova, D. Prog. Surf. Sci., 54(3/4), 249, 1997.

31. Koch, R.; Sturmat, M.; Schulz, J. J. Surf. Sci., 454-456, 543, 2000.

32. Li, J. T.; Berndt, R.; Gaisch, R.; Schneider, W.-D. J. Vac. Sci. Technol., B, 14(2), 1149,

1996.

33. Held, G. A.; Goodstein, D. M.; Feenstra, R. M.; Ramstad, M. J.; Noh, D. Y.; Birgeneau, R. J.

Phys. Rev. B: 48(11), 8458, 1993.

34. Ozcomert, J. S.; Pai, W. W.; Bartelt, N. C.; Reutt-Robey, J. E. Surf. Sci., 293(3), 183, 1993.

35. Hashizume, T.; Taniguchi, M.; Motai, K.; Lu, H.; Tanaka, K.; Sakurai, T., Jpn. J. Appl.

Phys., Part 2, 30(8B), L1529, 1991.

36. Koch, R.; Schulz, J. J.; Rieder, K. H. Europhys. Lett., 48(5), 554, 1999.

37. Morgenstern, K.; Rosenfeld, G.; Comsa, G.; Sorensen, M. R.; Hammer, B.; Laegsgaard, E.;

Besenbacher, F. Phys. Rev., B: 63(4), 045412/1, 2001.

38. Kim, H. S.; Zheng, Y. C.; Bryant, P. J. J. Vac. Sci. Technol., A, 8(1), 314, 1990.

39. Hoogeman, M. S.; Schlöβer, D. C.; Sanders, J. B.; Kuipers, L.; Frenken, J. W. M. Phys. Rev.

B: 53(20), R13299, 1996.

40. Buisset, J.; Rust, H.-P.; Schweizer, E. K.; Cramer, L.; Bradshaw, A. M. J. Vac. Sci. Technol.,

B, 14(2), 1117, 1996.

41. Doyen, G.; Drakova, D.; Barth, J. V.; Schuster, R.; Gritsch, T.; Behm, R. J.; Ertl, G. Phys.

Rev. B, 48(3), 1738, 1993.

42. Speller, S.; Bömermann, J.; Molitor, S.; Rauch, T.; Heiland, W. Surf. Sci., 331-333(Pt. B),

1070, 1995.

43. Gritsch, T.; Coulman, D.; Behm, R. J.; Ertl, G. Surf. Sci., 257(1-3), 297, 1991.

44. Speller, S.; Rauch, T.; Heiland, W. Surf. Sci., 342(1-3), 224, 1995.

45. Mizutani, W.; Ohi, A.; Motomatsu, M.; Tokumoto, H. Jpn. J. Appl. Phys., Part 2, 34(9A),

L1151, 1995.

46. Kaiser, W. J.; Jaklevic, R. C. Surf. Sci., 181(1-2), 55, 1987.

47. Brodde, A.; Tosch, S.; Neddermeyer, H. J. Microsc., 152(2), 441, 1988.

48. Wiesendanger, R.; Buergler, D.; Tarrach, G.; Anselmetti, D.; Hidber, H. R.; Güntherodt, H.

J. J. Vac. Sci. Technol., A, 8(1), 339, 1990.

49. Schott, J. H.; White, H. S. Langmuir, 8(8), 1955, 1992.

50. Snyder, S. R. J. Electrochem. Soc., 139(1), C5, 1992.

51. Hallmark, V. M.; Chiang, S.; Rabolt, J. F.; Swalen, J. D.; Wilson, R. J. Phys. Rev. Lett.,

59(25), 2879, 1987.

52. Pourmir, F.; Rousset, S.; Gauthier, S.; Sotto, M.; Klein, J. Microsc., Microanal., Microstruct.,

5(4/5/6), 269, 1994.

53. Borbonus, M.; Koch, R.; Haase, O.; Rieder, K. H. Surf. Sci., 249(1-3), L317, 1991.

54. Girard, J. C.; Samson, Y.; Gauthier, S.; Rousset, S.; Klein, J. Surf. Sci., 302(1-2), 73, 1994.

55. Urbaniak-Kucharczyk, A. Surf. Sci., 200(2-3), 247, 1988.

56. Girard, J. C.; Gauthier, S.; Rousset, S.; Klein, J. Microsc., Microanal., Microstruct., 4(5),

489, 1993.

57. Zou, Z. Q.; Dong, Z. C.; Trifonov, A. S.; Nejo, H. J. Vac. Sci. Technol., B: 20(4), 1567,

2002.

58. Samsavar, A.; Hirschorn, E. S.; Miller, T.; Leibsle, F. M.; Eades, J. A.; Chiang, T. C. Phys.

Rev. Lett., 65(13), 1607, 1990.

59. Hörmandinger, G. Phys. Rev. B, 49(19), 13897, 1994.

60. Reinecke, N.; Reiter, S.; Vetter, S.; Taglauer, E. Appl. Phys., A, 75(1), 1, 2002.

61. Molotkov, S. N.; Nazin, S. S. Surf. Sci., 304(1-2), 109, 1994.

62. Stroscio, J. A.; Pierce, D. T.; Davies, A.; Celotta, R. J.; Weinert, M. Phys. Rev. Lett., 75(16),

2960, 1995.

63. Kawagoe, T.; Tamura, E.; Suzuki, Y.; Koike, K. Phys. Rev. B: 65(2), 024406/1, 2002.

64. Hofer, W. A.; Redinger, J.; Biedermann, A.; Varga, P. Surf. Sci., 466(1-3), L795, 2000.

65. Heinze, S.; Blügel, S.; Pascal, R.; Bode, M.; Wiesendanger, R. Phys. Rev. B: 58(24), 16432,

1998.

66. Schulz, J. J.; Sturmat, M.; Koch, R. Phys. Rev. B: 62(23), 15402, 2000.

67. Kuntze, J.; Bomermann, J.; Rauch, T.; Speller, S.; Heiland, W. Surf. Sci., 394(1-3), 150,

1997.

68. Stelmashenko, N. A.; Walls, M. G.; Brown, L. M.; Milman, Y. V. Acta Metall. Mater.,

41(10), 2855, 1993.

69. Speller, S.; Heiland, W.; Biedermann, A.; Platzgummer, E.; Nagl, C.; Schmid, M.; Varga, P.

Surf. Sci., 331-333(Pt. B), 1056, 1995.

70. An, B.; Fukuyama, S.; Yokogawa, K.; Yoshimura, M. Appl. Surf. Sci., 130-132, 523, 1998.

71. Frohn, J.; Reynolds, J.; Engel, T. Surf. Sci., 320(1/2), 93, 1994.

72. Bischoff, M. M. J.; Konvicka, C.; Quinn, A. J.; Schmid, M.; Redinger, J.; Podloucky, R.;

Varga, P.; Van Kempen H. Surf. Sci., 513(1), 9, 2002.

73. Bischoff, M. M. J.; Konvicka, C.; Quinn, A. J.; Schmid, M.; Redinger, J.; Podloucky, R.;

Varga, P.; Van Kempen H. Phys. Rev. Lett., 86(11), 2396, 2001.

74. Wengelnik, H.; Badt, D.; Neddermeyer, H. Surf. Sci., Part B, 307-309(1-3), 619, 1994.

75. Losovyj, Y. B.; Ciszewski, A.; Zuber, Z. Physica Status Solidi B: 225(1), R6, 2001.

76. Hwang, R. Q.; Bartelt, M. C. Chem. Rev., 97, 1063, 1997.

77. Gewirth, A. A.; Niece, B. K. Chem. Rev., 97, 1129, 1997.

78. Lai, X.; Chusuei, C. C.; Luo, K.; Guo, Q.; Goodman, D. W. Chem. Phys. Lett., 330 (3-4),

226, 2000.

79. Fukui, K.; Namai, Y.; Iwasawa, Y. Appl. Surf. Sci., 188, 252, 2002.

80. Castell, M. R.; Dudarev, S. L.; Briggs, G. A. D.; Sutton, A. P. Phys. Rev. B: 59(11), 7342,

1999.

81. Castell, M. R.; Dudarev, S. L.; Muggelberg, C.; Sutton, A. P.; Briggs, G. A. D.; Goddard, D.

T. Microsc. Microanal., 6(4), 324, 2000.

82. Rizzetti, A.; Xhie, J.; Sattler, K.; Yamamoto, D.; Pong, W. J. Electron Spectrosc. Relat.

Phenom., 58(4), 359, 1992.

83. Condon, N. G.; Leibsle, F. M.; Lennie, A. R.; Murray, P. W.; Parker, T. M.; Vaughan, D. J.;

Thornton, G. Surf. Sci., 397(1-3), 278, 1998.

84. Wang, X.-G.; Weiss, W.; Shaikhutdinov, Sh. K.; Ritter, M.; Petersen, M.; Wagner, F.;

Schlogl, R.; Scheffler, M. Phys. Rev. Lett., 81(5), 1038, 1998.

85. Eggleston, C. M. Am. Mineral., 84(7-8), 1061, 1999.

86. Tarrach, G.; Burgler, D.; Schaub, T.; Wiesendanger, R.; Guntherodt, H.-J. Surf. Sci., 285(1-

2), 1, 1993.

87. Jansen, R.; Nelissen, B. J.; Abraham, D. L.; van Kempen, H.; Brabers, V. A. M. IEEE Trans.

Magn., 30(6, Pt. 1), 4506, 1994.

88. Jansen, R.; Brabers, V. A. M.; van Kempen, H. Surf. Sci., 328(3), 237, 1995.

89. Lennie, A. R.; Condon, N. G.; Leibsle, F. M.; Murray, P. W.; Thornton, G.; Vaughan, D. J.

Phys. Rev. B: 53(15), 10244, 1996.

90. Condon, N. G.; Leibsle, F. M.; Parker, T.; Lennie, A. R.; Vaughan, D. J.; Thornton, G. Phys.

Rev. B: 55(23), 15885, 1997.

91. Jansen, R.; van Kempen, H.; Wolf, R. M. J. Vac. Sci. Technol., B, 14(2), 1173, 1996.

92. Schoenenberger, C.; Alvarado, S. F.; Ortiz, C. J. Appl. Phys., 66(9), 4258, 1989.

93. Valeri, S.; Altieri, S.; del Pennino, U.; di Bona, A.; Luches, P.; Rota, A. Phys. Rev. B:

65(24), 245410/1, 2002.

94. Goonewardene, A. U.; Karunamuni, J.; Kurtz, R. L.; Stockbauer, R. L. Surf. Sci., 501(1-2),

102, 2002.

95. Castell, M. R.; Muggelberg, C.; Dudarev, S. L.; Sutton, A. P.; Briggs, G. A. D.; Goddard, D.

T. Appl. Phys. A: A66, S963, 1998.

96. Castell, M. R.; Wincott, P. L.; Condon, N. G.; Muggelberg, C.; Thornton, G.; Dudarev, S. L.;

Sutton, A. P.; Briggs, G. A. D. Phys. Rev. B: 55(12), 7859, 1997.

97. Hosoi, H.; Sueoka, K.; Hayakawa, K.; Mukasa, K. Appl. Surf. Sci., 157, 218. 2000.

98. Dudarev, S. L.; Liechtenstein, A. I.; Castell, M. R.; Briggs, G. A. D.; Sutton, A. P. Phys.

Rev. B: 56(8), 4900, 1997.

99. Bertrams, Th.; Neddermeyer, H. J. Vac. Sci. Technol., B, 14(2), 1141, 1996.

100. Hannemann, H.; Ventrice, C. A., Jr.; Bertrams, Th.; Brodde, A.; Neddermeyer, H. Phys.

Status Solidi A, 146(1), 289, 1994.

101. Zheng, G.; Altman, E. I. Surf. Sci., 504(1-3), 253, 2002.

102. Over, H.; Kim, Y. D.; Seitsonen, A. P.; Wendt, S.; Lundgren, E.; Schmid, M.; Varga, P.;

Morgante, A.; Ertl, G. Science, 287(5457), 1474, 2000.

103. Over, H.; Seitsonen, A. P.; Lundgren, E.; Schmid, M.; Varga, P. Surf. Sci., 515(1), 143,

2002.

104. Pang, C. L.; Haycock, S. A.; Raza, H.; Moller, P. J.; Thornton, G. Phys. Rev. B: 62

R7775, 2000.

105. Raza, H.; Pang, C. L.; Haycock, S. A.; Thornton, G. Appl. Surf. Sci., 140, 271, 1999.

106. Ruzycki, N.; Herman, G. S.; Boatner, L. A.; Diebold, U. Surface Science, 529(1-2),

L239. 2003.

107. Murray, P. W.; Leibsle, F. M.; Muryn, C. A.; Fisher, H. J.; Flipse, C. F. J.; Thornton, G.

Phys. Rev. Lett., 72(5), 689, 1994.

108. Onishi, H.; Fukui, K.; Iwasawa, Y. Bull. Chem. Soc. Jpn., 68(9), 2447, 1995.

109. Bennett, R. A.; Stone, P.; Bowker, M. Faraday Discuss., 114, 267, 1999.

110. Smith, R. D.; Bennett, R. A.; Bowker, M. Phys. Rev., B, 66, 035409, 2002.

111. Berko, A.; Solymosi, F. Langmuir, 12(5), 1257, 1996.

112. Szabo, A.; Engel, T. Surf. Sci., 329(3), 241, 1995.

113. Fischer, S.; Munz, A. W.; Schierbaum, K. D.; Göpel, W. J. Vac. Sci. Technol., B, 14(2),

961, 1996.

114. Novak, D.; Garfunkel, E.; Gustafsson, T. Phys. Rev. B, 50(7), 5000, 1994.

115. Takakusagi, S.; Fukui, K.I.; Nariyuki, F.; Iwasawa, Y. Surface Science, 523(1-2), L41,

2003.

116. Diebold, U.; Li, M.; Dulub, O.; Hebenstreit, E. L. D.; Hebenstreit, W. Surf. Rev. Lett.,

7(5 & 6), 613, 2000.

117. Fukui, K.; Onishi, H.; Iwasawa, Y. Phys. Rev. Lett., 79, 4202, 1997.

118. Asari, E.; Souda, R. Surf. Sci., 486(3), 203, 2001.

119. Rohrer, G. S.; Henrich, V. E.; Bonnell, D. A. Surf. Sci., 278(1-2), 146, 1992.

120. Smith, R. L.; Lu, W.; Rohrer, G. S., Surf. Sci., 322(1-3), 293, 1995.

121. Oshio, T.; Sakai, Y.; Ehara, S. J. Vac. Sci. Technol., B, 12(3), 2055, 1994.

122. Jones, F. H.; Dixon, R. A.; Brown, A. Surf. Sci., 369(1-3), 343, 1996.

123. Tanner, R. E.; Altman, E. I. J. Vac. Sci. Technol., A: 19(4, Pt. 1), 1502, 2001.

124. Egdell, R. G.; Jones, F. H. J. Mater. Chem., 8(3), 469, 1998.

125. Ganz, E.; Sattler, K.; Clarke, J. Surf. Sci., 219(1-2), 33, 1989.

126. Ganz, E.; Sattler, K.; Clarke, J. J. Vac. Sci. Technol., A, 6(2), 419, 1988.

127. Maurice, V.; Marcus, P. Surf. Sci., 275(1-2), 65, 1992.

128. Patrin, J. C.; Li, Y. Z.; Weaver, J. H. Phys. Rev. B: 45(4), 1756, 1992.

129. Jia, Jinfeng; Wang, Jun-Zhong; Liu, Xi; Xue, Qi-Kun; Li, Zhi-Qiang; Kawazoe, Y.;

Zhang, S. B. Appl. Phys. Lett., 80(17), 3186, 2002.

130. Endo, T.; Sumomogi, T.; Maeta, H.; Ohara, S; Fujita, H. Mater. Trans., JIM, 40(9), 903,

1999.

131. Hu, X. M.; von Blanckenhagen, P. J. Vac. Sci. Technol., B, 17(2), 265, 1999.

132. Lai, X.; Xu, C.; Goodman, D. W. J. Vac. Sci. Technol., A, 16(4), 2562, 1998.

133. Hu, Xiaoming; von Blanckenhagen, P. Appl. Phys. A, A66, S707, 1998.

134. Ohnishi, H.; Yamamoto, Y.; Katayama, I.; Ohba, Y.; Oura, K. Jpn. J. Appl. Phys., Part 2,

33(8A), L1106, 1994.

135. Grimaud, C-M.; Palmer, R. E. J. Phys.: Condensed Matter, 13(9), 1869, 2001.

136. Kenny, D. J.; Weller, S. C.; Couillard, M.; Palmer, R. E.; Sanz-Navarro, C. F.; Smith, R.

Euro. Phys. J. D: 16(1-3), 115, 2001.

137. Jödicke, H.; Schaub, R.; Bhowmick, A.; Monot, R.; Buttet, J.; Harbich, W. Rev. Sci.

Instrum., 71(7), 2818, 2000.

138. Gubin, S. P.; Soldatov, E. S.; Trifonov, A. S.; Khanin, V. V. Inorg. Mater., 32, 1111,

1996.

139. Hövel, H.; Becker, T.; Bettac, A.; Reihl, B.; Tschudy, M.; Williams, E. J. J. Appl. Phys.,

81, 154, 1997.

140. Park, K.-H.; Ha, J. S.; Yun, W. S.; Ko, Y.-J. Jpn. J. Appl. Phys., Part 1, 39(7B), 4629,

2000.

141. Lai, X. F.; St. Clair, T. P.; Goodman, D.W. Faraday Discuss., 114, 279, 1999.

142. Park, K.-H.; Shin, M.; Ha, J. S.; Yun, W. S.; Ko, Y.-J. Appl. Phys. Lett., 75(1), 139, 1999.

143. Vinod, C. P.; Kulkarni, G. U.; Rao, C. N. R. Chem. Phys. Lett., 289(3,4), 329, 1998.

144. Downes, A.; Welland, M. E. Appl. Phys. Lett., 72(21), 2671, 1998.

145. Jiang, C.-S.; Nakayama, T.; Aono, M. Appl. Surf. Sci., 130-132, 425, 1998.

146. Ohba, Y.; Katayama, I.; Numata, T.; Ohnishi, H.; Watamori, M.; Oura, K. Appl. Surf.

Sci., 121/122, 191, 1997.

147. Santra, A. K.; Min, B. K.; Goodman, D. W. Surf. Sci., 515(1), L475, 2002.

148. Baro, A. M.; Bartolome, A.; Vazquez, L.; Garcia, N.; Reifenberger, R.; Choi, E.; Andres,

R. P. Appl. Phys. Lett., 51(20), 1594, 1987.

149. Hou, S. M.; Tao, C. G.; Liu, H. W.; Zhao, X. Y.; Liu, W. M.; Xue, Z. Q. Sci. in China,

Series E, 44(4), 398, 2001.

150. Hu, C. W.; Kasuya, A.; Wawro, A.; Horiguchi, N.; Czajka, R.; Nishina, Y.; Saito, Y.;

Fujita, H. Mater. Sci. Eng., A, A217/218, 103, 1996.

151. Mitchell, C. E. J.; Howard, A.; Carney, M.; Egdell, R. G. Surf. Sci., 490(1-2), 196, 2001.

152. Wang, B.; Xiao, X. D.; Huang, X. X.; Sheng, P.; Hou, J. G. Appl. Phys. Lett., 77(8), 1179,

2000.

153. Humbert, A.; Dayez, M.; Sangay, S.; Chapon, C.; Henry, C. R. J. Vac. Sci. Technol., A,

8(1), 311, 1990.

154. Valden, M.; Lai, X.; Goodman, D. W. Science, 281(5383), 1647, 1998.

155. Ruan, L.; Chen, D. M. Surf. Sci., 393(1-3), L113, 1997.

156. Saito, Y.; Murata, K.; Hamaguchi, K.; Fujita, H.; Kotake, S.; Suzuki, Y.; Senoo, M.; Hu,

C. -W.; Kasuya, A.; Nishina, Y. J. Cluster Sci., 9(2), 123, 1998.

157. Xu, C.; Oh, W. S.; Liu, G.; Kim, D. Y.; Goodman, D. W. J. Vac. Sci. Technol., A, 15(3,

Pt. 2), 1261, 1997.

158. Hövel, H.; Becker, Th.; Bettac, A.; Reihl, B.; Tschudy, M.; Williams, E. J. Appl. Surf.

Sci., 115(2), 124, 1997.

159. Strbac, S.; Rakocevic, Z.; Nenadovic, T. J. Serb. Chem. Soc., 61(12), 1203, 1996.

160. Jiang, Q. D.; Fujita, D.; Sheng, H. Y.; Dong, Z. C.; Nejoh, H. Appl. Phys., A, A64, 619,

1997.

161. Becker, C.; Fries, T.; Wandelt, K.; Kreibig, U.; Schmid, G. J. Vac. Sci. Technol., B, 9(2),

810, 1991.

162. Wierenga, H. A.; Soethout, L.; Gerritsen, Jan W.; Van de Leemput, B. E. C.; Van

Kempen, H.; Schmid, G. Adv. Mater. 2(10), 482, 1990.

163. Van de Leemput, L. E. C.; Gerritsen, J. W.; Rongen, P. H. H.; Smokers, R. T. M.;

Wierenga, H. A.; Van Kempen, H.; Schmid, G. J. Vac. Sci. Technol., B, 9(2), 814, 1991.

164. Bigioni, T. P.; Harrell, L. E.; Gullen, W. G.; Guthrie, D. K.; Whetten, R. L.; First, P. N.

Eur. Phys. J. D, 6(3), 355, 1999.

165. Chi, L. F.; Rakers, S.; Hartig, M.; Gleiche, M.; Fuchs, H.; Schmid, G. Colloids Surf., A,

171(1-3), 241, 2000.

166. Chi, L. F.; Hartig, M.; Drechsler, T.; Schwaack, T.; Seidel, C.; Fuchs, H.; Schmid, G.

Appl. Phys. A: Mater. Sci. A66, S187, 1998.

167. Durston, P. J.; Schmidt, J.; Palmer, R. E.; Wilcoxon, J. P. Appl. Phys. Lett., 71(20), 2940,

1997.

168. Xu, H.; Ng, K. Y. S. J. Vac. Sci. Technol., B, 13(6), 2160, 1995.

169. Wawro, A.; Kasuya, A. Acta Phys. Pol., A, 93(2), 443, 1998.

170. Kandel, S. A.; Weiss, P. S. J. Phys. Chem., B, 105(34), 8102, 2001.

171. Chado, I.; Padovani, S.; Scheurer, F.; Bucher, J. P. Appl. Surf. Sci., 164, 42, 2000.

172. Padovani, S.; Chado, I.; Scheurer, F.; Bucher, J. P. Phys. Rev. B: 59(18), 11887, 1999.

173. Izquierdo, J.; Vega, A.; Balbas, L. C. Phys. Rev. B: 55(1), 445, 1997.

174. Okawa, Y.; Matsumoto, Y.; Tanaka, K. RIKEN Rev., 17, 37, 1998.

175. Whelan, C. M.; Barnes, C. J. Appl. Surf. Sci., 119(3/4), 288, 1997.

176. Wu, Q. F.; Chen, W. H.; Madey, T. E. J. Phys. Chem. B, 106(25), 6419, 2002.

177. Chen, D. A.; Bartelt, M. C.; Hwang, R. Q.; McCarty, K. F. Surf. Sci., 450 (1-2), 78, 2000.

178. Kolb, D. M.; Ullmann, R.; Will, T. Science, 275(5303), 1097, 1997.

179. Berko, A.; Solymosi, F. Surf. Sci., 411(3), L900, 1998.

180. Xu, H.; Ng, K. Y. S. J. Vac. Sci. Technol., B, 15(2), 186, 1997.

181. Helveg, S.; Lauritsen, J. V.; Laegsgaard, E.; Stensgaard, I.; Norskov, J. K.; Clausen, B. S.;

Topsoe, H.; Besenbacher, F. Phys. Rev. Lett., 84(5), 951, 2000.

182. Sakashita, Y.; Aoki, N.; Yoneda, T. Stud. Surf. Sci. Catal., 121, 403, 1999.

183. Shen, J.; Zhu, C.; Ma, Z.; Pang, S.; Xue, Z. Q. Appl. Surf. Sci., 60-61, 648, 1992.

184. Susla, B.; Czajka, R.; Szuba, S.; Kaminski, M.; Hihara, T.; Kasuya, A.; Sumiyama, K.

Colloids Surf., A: 202(2-3), 187, 2002.

185. Bifone, A.; Casalis, L.; Riva, R. Phys. Rev. B: 51(16), 11043, 1995.

186. Aiyer, H. N.; Vijayakrishnan, V.; Subbanna, G. N.; Rao, C. N. R. Surf. Sci., 313(3), 392,

1994.

187. Granjeaud, S.; Yckache, K.; Dayez, M.; Humbert, A.; Chapon, C.; Henry, C. R. Microsc.,

Microanal., Microstruct., 4(5), 409, 1993.

188. Yeung, K. L.; Wolf, E. E. J. Vac. Sci. Technol., A, 10(4), 651, 1992.

189. Piednoir, A.; Perrot, E.; Granjeaud, S.; Humbert, A.; Chapon, C.; Henry, C. R. Surf. Sci.,

391(1-3), 19, 1997.

190. Poulin, J. C.; Kagan, H. B.; Vargaftik, M. N.; Stolarov, I. P.; Moiseev, I. I. J. Mol. Catal.

A: Chem., 95(2), 109, 1995.

191. Reetz, M. T.; Helbig, W.; Quaiser, S. A.; Stimming, U.; Breuer, N.; Vogel, R. Science,

267(5196), 367, 1995.

192. Li, F. L.; Zhang, B. L.; Wang, E. K.; Dong, S. J. J. Electroanal. Chem., 422(1-2), 27,

1997.

193. Ma, Z. L.; Zhu, C. X.; Shen, J.; Pang, S. J.; Xue, Z. Q. Vacuum, 43(11), 1115, 1992.

194. Lee, S.; Permana, H.; Ng, K. Y. S. Catal. Lett., 23(3-4), 281, 1994.

195. Lee, S.; Permana, H.; Ng, K. Y. S. Stud. Surf. Sci. Catal., 75, 1863, 1993.

196. Yeung, K. L.; Wolf, E. E. J. Vac. Sci. Technol., B, 9(2), 798, 1991.

197. Yeung, K. L.; Wolf, E. E. Catal. Lett., 12 (1-3), 213, 1992.

198. Yeung, K. L.; Wolf, E. E. J. Catal. 135 (1), 13, 1992.

199. El-Azab, A.; Gan, S.; Liang, Y. Surf. Sci., 506(1-2), 93, 2002.

200. Somorjai, G. A. Appl. Surf. Sci., 121/122, 1, 1997.

201. Szoko, J.; Berko, A. Vacuum, 71(1-2), 193, 2003.

202. Dubois, J. G. A.; Gerritsen, J. W.; Schmid, G.; van Kempen, H. Physica B, 218(1-4), 262,

1996.

203. Fujimoto, T.; Fukuoka, A.; Ichikawa, M. Chem. Mater., 4(1), 104, 1992.

204. Watanabe, M. O.; Uchida, N.; Kanayama, T. Phys. Rev. B: 61(11), 7219, 2000.

205. Khosravi, A. A.; Kundu, M.; Kuruvilla, B. A.; Shekhawat, G. S.; Gupta, R. P.; Sharma, A.

K.; Vyas, P. D.; Kulkarni, S. K. App. Phys. Lett., 67, 2506, 1995.

206. Yamamoto, S.; Matsuoka, O.; Fukada, I.; Ashida, Y.; Honda, T.; Yamamoto, N. J. Catal.,

159, 401, 1996.

207. Somorjai, G. A. CATTECH, 3(1), 84, 1999.

208. Dishner, M. H.; Hemminger, J. C.; Feher, F. J. Langmuir, 13, 2318, 1997.

209. Chambliss, D. D.; Wilson, R. J. J. Vac. Sci. Technol., B, 9, 928, 1991.

210. Chambliss, D. D.; Wilson, R. J. Chiang, S. J. Vac. Sci. Technol., B, 9, 933, 1991.

211. Sander, M.; Engel, T. Surf. Sci., 302, L263, 1994.

212. Onishi, H.; Iwasawa, Y. Surf. Sci., 313, L783, 1994.

213. Pang, C. L.; Haycock, S. A.; Raza, H.; Murray, P. W.; Thornton, G.; Gülseren, O.; James,

R.; Bullett, D. W. Phys. Rev. B, 58, 1586, 1998.

214. Asari, E.; Souda, R. Appl. Surf. Sci., 193, 70, 2002.

215. Diebold, U.; Lehman, J.; Mahmoud, T.; Kuhn, M.; Leonardelli, G.; Hebenstreit, W.;

Schmid, M.; Varga, P. Surf. Sci., 411, 137, 1998.

216. Smith, R. D.; Bennett, R. A.; Bowker, M. Phys. Rev., B, 66, 035409, 2002.

217. Yeung, K. L.; Maira, A. J.; Stolz, J.; Hung, E. W. C.; Ho, N. K. C.; Wei, A.-C.; Soria, J.;

Chao, K.-J.; Yue, P.-L. J. Phys. Chem. B, 106, 4608, 2002.

218. Maira, A. J.; Yeung, K. L.; Lee, C. Y.; Yue, P. L.; Chan, C. K. J. Catal., 192, 185, 2000.

219. Maira, A. J.; Yeung, K. L.; Chan, C. K.; Porter, J. F.; Yue, P. L. Stud. in Surf. Sci. and

Catal., 130, 1949, 2000.

220. Maira, A. J.; Yeung, K. L.; Soria, J.; Coronado, J. M.; Belver, C.; Lee C. Y.; Augugliaro,

V. Appl. Catal. B Environmental, 29, 327, 2001.

221. Lee, S.-J.; Gavriilidis, A.; Pankhurst, Q. A.; Kyek, A.; Wagner, F. E.; Wong, P. C. L.;

Yeung, K. L. J. Catal., 200, 298, 2001.

222. Coronado, J. M.; Maira, A. J.; Conesa, J. C.; Yeung, K. L.; Augugliaro, V.; Soria, J.

Langmuir, 17, 5368, 2001.

223. Maira, A. J.; Coronado, J. M.; Augugliaro, V.; Yeung, K. L.; Conesa, J. C.; Soria, J. J.

Catal., 202, 413, 2001.

224. Occelli, M. L.; Drake, B.; Gould, S. A. C. J. Catal., 142, 337, 1993.

225. Valden, M.; Pak, S.; Lai, X.; Goodman, D. W. Catal. Lett., 56 (1), 7, 1998.

226. Haruta, M.; Tsubota, S.; Kobayashi, T.; Kageyama, H.; Genet, M. J.; Delmon, B. J.

Catal., 144, 175, 1993.

227. Lin, S. D.; Bollinger, M.; Vannice, M. A. Catal. Lett., 17, 245, 1993.

228. Hayashi, T.; Tanaka, K.; Haruta, M. J. Catal., 178, 566, 1998.

229. Stangland, E. E.; Stavens, K. B.; Andres, R. P.; Delgass, W. N. J. Catal., 191, 332, 2000.

230. Haruta, M.; Date, M. Appl. Catal. A, General, 222 (1-2), 427, 2001.

231. Haruta, M. Catalysis Today, 36, 153, 1997.

232. Kolmakov, A.; Goodman, D. W. Catal. Lett, 70, 93, 2000.

233. Sykes, E. C. H.; Williams, F. J.; Tikhov, M. S.; Lambert, R. M. J. Phys. Chem., B, 106,

5390, 2002.

234. Kolmakov, A.; Goodman, D. W. Surf. Sci., 490, L597, 2001.

235. Lai, X. F.; Goodman, D. W. J. Mol. Catal., A: Chem., 162, 33, 2000.

236. Meier, D. C.; Lai, X. F.; Goodman, D. W. Surface Chemistry and Catalysis, 147-189.

Edited by: Carley, Albert F. Kluwer Academic/Plenum Publishers: New York, N. Y.,

2002.

237. Chusuei, C. C.; Lai, X.; Davis, K. A.; Bowers, E. K.; Fackler, J. P.; Goodman, D. W.

Langmuir, 17, 4113, 2001.

238. Fukui, Ken-ichi; Sugiyama, S.; Iwasawa, Y. Phys. Chem. Chem. Phys., 3, 3871, 2001.

239. Biener, J.; Wang, J.; Madix, R. J. Surf. Sci., 442, 47, 1999.

240. Biener, J.; Bäumer, M.; Wang, J.; Madix, R. J. Surf. Sci., 450, 12, 2000.

241. Reddic, J. E.; Zhou, J.; Chen, D. A. Surf. Sci., 494, L767, 2001.

242. Chen, D. A.; Bartelt, M. C.; Seutter, S. M.; McCarty, K. F. Surf. Sci., 464, L708, 2000.

243. Hotsenpiller, P. A. M.; Bolt, J. D.; Farneth, W. E.; Lowekamp, J. B.; Rohrer, G. S. J. Phys.

Chem., B, 102, 3216, 1998.

244. Murray, P. W.; Shen, J.; Condon, N. G.; Pang, S. J.; Thornton, G. Surf. Sci., 380, L455,

1997.

245. Howard, A.; Mitchell, C. E. J.; Egdell, R. G. Surf. Sci., 515, L504, 2002.

246. Gan, S.; El-azab, A.; Liang, Y. Surf. Sci., 479, L369, 2001.

247. Dulub, O.; Hebenstreit, W.; Diebold, U. Phys. Rev. Lett., 84(16), 3646, 2000.

248. Brookshier, M. A.; Chusuei, C. C.; Goodman, D. W. Langmuir, 15, 2043, 1999.

249. Partridge, A.; Toussaint, S. L. G.; Flipse, C. F. J.; van IJzendoorn, L. J.; van den Oetelaar,

L. C. A. J. Vac. Sci. Technol. B 14(2), 585, 1996.

250. Schild, Ch.; Engweiler, J.; Nickl, J.; Baiker, A.; Hund, M.; Kilo, M.; Wokaun, A. Catal.

Lett., 25, 179, 1994.

251. Schildenberger, M.; Prins, R.; Bonetti, Y. C. J. Phys. Chem. B, 104, 3250, 2000.

252. Wei, T.-C.; Phillips, J. Adv. Catal. 41, 359, 1996.

253. Tsirlin, T.; Zhu, J.; Grunes, J.; Somorjai, G. A. Topics in Catalysis, 19(2), 165, 2002.

254. Okumura, K.; Hyodo, S.-A.; Noda, S.; Maruyama, Y. J. Phys. Chem., B, 102, 2350, 1998.

255. Wodiunig, S.; Keel, J. M.; Wilson, T. S. E.; Zemichael, F. W.; Lambert, R. M. Catalysis

Letters, 87(1-2), 1, 2003.

256. Wintterlin, J.; Brune, H.; Höfer, H.; Behm, R. J. Appl. Phys. A, A47(1), 99, 1988.

257. Brune, H.; Wintterlin, J.; Trost, J.; Ertl, G.; Wiechers, J.; Behm, R. J. J. Chem. Phys.,

99(3), 2128, 1993.

258. Pascual, J. I.; Jackiw, J. J.; Song, Z.; Weiss, P. S.; Conrad, H.; Rust, H.-P. Surf. Sci., 502-

503, 1, 2002.

259. Sakurai, T.; Hashizume, T.; Lu, H. Vacuum, 43(11), 1107, 1992.

260. Hashizume, T.; Taniguchi, M.; Motai, K.; Lu, H.; Tanaka, K.; Sakurai, T. Surf. Sci.,

266(1-3), 282, 1992.

261. Hashizume, T.; Rowe, J. E.; Malic, R. A.; Motai, K.; Cho, K.; Kishimoto, J.; Sakurai, T. J.

Vac. Sci. Technol., B, 12(3), 1809, 1994.

262. Barth, J. V.; Zambelli, T.; Wintterlin, J.; Ertl, G. Chem. Phys. Lett., 270(1,2), 152, 1997.

263. Weaver, M. J.; Gao, X. P.; Zhang, Y. J. Phys. Chem., 96(2), 510, 1992.

264. Gimzewski, J. K.; Modesti, S.; David, T.; Schlittler, R. R. J. Vac. Sci. Technol., B, 12(3),

1942, 1994.

265. Howells, S.; Chen, T.; Gallagher, M.; Sarid, D.; Lichtenberger, D. L.; Wright, L. L.; Ray,

C. D.; Huffman, D. R.; Lamb, L. D. Surf. Sci., 274(1), 141, 1992.

266. Rogero, C.; Pascual, J. I.; Gomez-Herrero, J.; Baro, A. M. J. Chem. Phys., 116(2), 832,

2002.

267. Laakso, A.; Lahtinen, J.; Levlin, M.; Hautojarvi, P. J. Chem. Phys., 115(8), 3763, 2001.

268. Ramsvik, T.; Borg, A.; Venvik, H. J.; Hansteen, F.; Kildemo, M.; Worren, T. Surf. Sci.,

499(2-3), 183, 2002.

269. Wöll, C.; Wilson, R. J.; Chiang, S.; Zeng, H. C.; Mitchell, K. A. R. Phys. Rev. B: 42(18),

11926, 1990.

270. Leibsle, F. M.; Flipse, C. F. J.; Robinson, A. W. Phys. Rev. B: 47(23), 15865, 1993.

271. Doering, M.; Rust, H.-P.; Briner, B. G.; Bradshaw, A. M. Surf. Sci., 410(2/3), L736, 1998.

272. Pedersen, M.O.; Murray, P.W.; Laegsgaard, E.; Stensgaard, I.; Besenbacher, F. Surf. Sci.,

389(1-3), 300, 1997.

273. Coulman, D.; Wintterlin, J.; Barth, J. V.; Ertl, G.; Behm, R. J. Surf. Sci., 240(1-3), 151,

1990.

274. Kuk, Y.; Chua, F. M.; Silverman, P. J.; Meyer, J. A. Phys. Rev. B: 41(18), 12393, 1990.

275. Chua, F. M.; Kuk, Y.; Silverman, P. J. Phys. Rev. Lett., 63(4), 386, 1989.

276. Buisset, J.; Rust, H.-P.; Schweizer, E. K.; Cramer, L.; Bradshaw, A. M. Surf. Sci., 349(3),

L147, 1996.

277. Motai, K.; Hashizume, T.; Shinohara, H.; Saito, Y.; Pickering, H. W.; Nishina, Y.;

Sakurai, T. Jpn. J. Appl. Phys., Part 2, 32(3B), L450, 1993.

278. Matsumoto, T.; Bennett, R. A.; Stone, P.; Yamada, T.; Domen, K.; Bowker, M. Surf. Sci.,

471(1-3), 225, 2001.

279. Kopatzki, E.; Behm, R. J. Surf. Sci., 245(3), 255, 1991.

280. Takehiro, N.; Matsumoto, Y.; Okawa, Y.; Tanaka, K. Phys. Rev. B: 53(7), 4094, 1996.

281. Ichihara, S.; Yoshinobu, J.; Ogasawara, H.; Nantoh, M.; Kawai, M.; Domen, K. J.

Electron Spectrosc. Relat. Phenom., 88-91, 1003, 1998.

282. Katano, S.; Ichihara, S.; Ogasawara, H.; Kato, H. S.; Komeda, T.; Kawai, M.; Domen, K.

Surf. Sci., 502-503, 164, 2002.

283. Kim, J. T.; Kawai, T.; Yoshinobu, J.; Kawai, M. Surf. Sci., 360(1-3), 50, 1996.

284. Komeda, T.; Fukidome, H.; Kim, Y.; Kawai, M.; Sainoo, Y.; Shigekawa, H. Jpn. J. Appl.

Phys., Part 1: 41(7B), 4932, 2002.

285. Rose, M. K.; Mitsui, T.; Dunphy, J.; Borg, A.; Ogletree, D. F.; Salmeron, M.; Sautet, P.

Surf. Sci., 512(1-2), 48, 2002.

286. Hansen K. H.; Sljivancanin, Z.; Hammer, B.; Laegsgaard, E.; Besenbacher, F.; Stensgaard,

I. Surf. Sci., 496(1-2), 1, 2002.

287. Janin, E.; von Schenck, H.; Gothelid, M.; Karlsson, U. O.; Svensson, M. Phys. Rev. B:

61(19), 13144, 2000.

288. Nakagoe, O.; Takagi, N.; Matsumoto, Y. Surf. Sci., 514(1-3), 414, 2002.

289. Morgenstern, M.; Müller, J.; Michely, T.; Comsa, G. Z. Phys. Chem., 198(1/2), 43, 1997.

290. Matsumoto, M.; Fukutani, K.; Okano, T.; Miyake, K.; Shigekawa, H.; Kato, H.; Okuyama,

H.; Kawai, M. Surf. Sci., 454-456, 101, 2000.

291. Horch, S.; Zeppenfeld, P.; Comsa, G. Appl. Phys. A: A60(2), 147, 1995.

292. Nagl, C.; Schuster, R.; Renisch, S.; Ertl, G. Phys. Rev. Lett., 81(16), 3483, 1998.

293. Nilius, N.; Mitte, M.; Neddermeyer, H. Appl. Phys. A: A66, S519, 1998.

294. Jensen, J. A.; Rider, K. B.; Chen, Y.; Salmeron, M.; Somorjai, G. A. J. Vac. Sci. Technol.

B. 17(3), 1080, 1999.

295. Rider, K. B.; Hwang, K. S.; Salmeron, M.; Somorjai, G. A. J. Am. Chem. Soc., 124, 5588,

2002.

296. Onishi, H.; Iwasawa, Y. Surf. Sci., 357-358, 773, 1996.

297. Suzuki, S.; Fukui, Ken-ichi; Onishi, H.; Iwasawa, Y. Phys. Rev. Lett., 84(10), 2156, 2000.

298. Suzuki, S.; Yamaguchi, Y.; Onishi, H.; Fukui, K. I.; Sasaki, T.; Iwasawa, Y. Catal. Lett.,

50, 117, 1998.

299. Suzuki, S.; Onishi, H.; Sasaki, T.; Fukui, K. I.; Iwasawa, Y. Catal. Lett., 54, 177, 1998.

300. Tero, R.; Fukui, K.; Iwasawa, Y. J. Phys. Chem., B, 107(14), 3207, 2003.

301. Onishi, H.; Sasahara, A.; Uetsuka, H.; Ishibashi, T. Appl. Surf. Sci., 188, 257, 2002.

302. Sasahara, A.; Uetsuka, H.; Ishibashi, T. Onishi, H. Appl. Surf. Sci., 188, 265, 2002.

303. Tanner, R. E.; Sasahara, A.; Liang, Y.; Altman, E. I.; Onishi, H. J. Phys. Chem., B, 106,

8211, 2002.

304. Wiesendanger, R. Scanning Probe Microscopy and Spectroscopy, Methods and

applications, Cambridge University Press, 1994.

305. Binnig, G.; Fuchs, H.; Stoll, E. Surf. Sci., 169, L295, 1986.

306. Tsong, T. T. Prog. Surf. Sci., 67, 235, 2001.

307. Lo, R. L.; Hwang, I. S.; Ho, M. S.; Tsong, T. T. Phys. Rev. Lett., 80(25), 5584, 1998.

308. Hwang, I. S.; Lo, R. L.; Tsong, T. T. Phys. Rev. Lett., 78(25), 4797,1997.

309. Mo, Y. W.; Kleiner, J.; Webb, M. B.; Lagally, M. G. Phys. Rev. Lett., 66(15), 1998, 1991.

310. Mo, Y. W.; Kariotis, R.; Swartzentruber, B. S.; Webb, M. B.; Lagally, M. G. J. Vac. Sci.

Technol. A, 8(1), 201, 1990.

311. Linderoth, T. R.; Horch, S.; Laegsgaard, E.; Stensgaard, I.; Besenbacher, F. Phys. Rev.

Lett., 78(26), 4978, 1997.

312. Venables, J. A.; Spiller, G. D. T.; Hanbuecken, M. Rep. Prog. Phys. 47, 399, 1984.

313. Wen, J. M.; Chang, S. L., Burnett, J. W.; Evans, J. W.; Thiel, P. A. Phys. Rev. Lett.,

73(19), 2591, 1994.

314. Hwang, I. S.; Ho, M. S.; Tsong, T. T. Phys. Rev. Lett., 83(1), 120, 1999.

315. Hwang, I. S.; Ho, M. S.; Tsong, T. T. Surf. Sci., 514, 309, 2002.

316. Hwang, I. S.; Ho, M. S.; Tsong, T. T. J. Phys. Chem. Solid., 62(9-10), 1655, 2001.

317. Wolf, J. F.; Vicenzi, B.; Ibach, H. Surf. Sci., 249(1-3), 233, 1991.

318. Frohn, J.; Giesen, M.; Poensgen, M.; Wolf, J. F.; Ibach, H. Phys. Rev. Lett., 67(25), 3543,

1991.

319. Kuipers, L.; Hoogeman, M. S.; Frenken, J. W. M. Phys. Rev. Lett., 71(21), 3517, 1993.

320. Gimzewski, J. K.; Berndt, R.; Schlittler, R. R. Phys. Rev. B, 45(12), 6844, 1992.

321. Gimzewski, J. K.; Berndt, R.; Schlittler, R. R. J. Vac. Sci. Technol., B, 9(2), 897, 1991.

322. Gimzewski, J. K.; Berndt, R.; Schlittler, R. R. Surf. Sci., 247, 327, 1991.

323. Frenken, J. W. M.; van Gastel, R.; van Albada, S. B.; Somfai, E.; van Saarloos, W. Appl.

Phys. A, 75, 11, 2002.

324. van Gastel, R.; Somfai, E.; van Saarloos, W.; Frenken, J. W. M. Nature, 408, 665, 2000.

325. van Gastel, R.; Somfai, E.; van Albada, S. B.; van Saarloos, W.; Frenken, J. W. M. Phys.

Rev. Lett., 86(8), 1562, 2001.

326. Morgenstern, K.; Rosenfeld, G.; Poelsema, B.; Comsa, G. Phys. Rev. Lett., 74(11), 2058,

1995.

327. Cremer, P. S.; Su, X. C.; Shen, Y. R.; Somorjai, G. A. Catal. Lett., 40, 143, 1996.

328. Huang, W. X.; Bao, X. H.; Rotermund, H. H.; Ertl, G. J. Phys. Chem., B, 106, 5645, 2002.

329. Murray P. W.; Besenbacher, F.; Stensgaard, I. Isr. J. Chem., 36, 25, 1996.

330. Leibsle, F. M.; Murray, P. W.; Condon, N. G.; Thornton, G. J. Phys. D, 30, 741, 1997.

331. Ertl, G. J. Mol. Catal., A, Chem. 182-183, 5, 2002.

332. Atamny, F.; Baiker, A. Appl. Catal. A: General, 173, 201, 1998.

333. Dürr, M.; Biedermann, A.; Hu, Z.; Höfer, U.; Heinz, T. F. Science, 296, 1838, 2002.

334. Teague, L. C.; Boland, J. J. J. Phys. Chem. B, 107(16), 3820, 2003.

335. Zambelli, T.; Wintterlin, J.; Trost, J.; Ertl, G. Science, 273, 1688, 1996.

336. Sachs, C.; Hildebrand, M.; Völkening, S.; Wintterlin, J.; Ertl, G. Science, 293, 1635, 2001.

337. Mitsui, T.; Rose, M. K.; Fomin, E.; Ogletree, D. F.; Salmeron, M. J. Chem. Phys.,

117(12), 5855, 2002.

338. Wintterlin, J.; Völkening, S.; Janssens, T. V. W.; Zambelli, T.; Ertl, G. Science, 278,

1931, 1997.

339. Hendriksen, B. L. M.; Frenken, J. W. M. Phys. Rev. Lett., 89(4), 046101, 2002.

340. Over, H.; Kim, Y. D.; Seitsonen, A. P.; Wendt, S.; Lundgren, E.; Schmid, M.; Varga, P.;

Morgante, A.; Ertl, G. Science, 287, 1474, 2000.

341. Over, H.; Seitsonen, A. P.; Lundgren, E.; Schmid, M.; Varga, P. J. Amer. Chem. Soc.,

123, 11807, 2001.

342. Nakagoe, O.; Watanabe, K.; Takagi, N.; Matsumoto, Y. Physical Review Letters, 90(22),

226105/1, 2003.

343. Leibsle, F. M.; Francis, S. M.; Davis, R.; Xiang, N.; Haq, S.; Bowker, M. Phys. Rev. Lett.,

72, 2569, 1994.

344. Francis, S. M.; Leibsle, F. M.; Haq, S.; Xiang, N.; Bowker, M. Surf. Sci., 315, 284, 1994.

345. Leibsle, F. M.; Francis, S. M.; Haq, S.; Bowker, M. Surf. Sci., 318, 46, 1994.

346. Bowker, M.; Rowbotham, E.; Leibsle, F. M.; Haq, S. Surf. Sci., 349, 97, 1996.

347. Haq, S.; Leibsle, F. M. Surf. Sci., 375, 81, 1997.

348. Scheibe, A.; Guenther, S.; Imbihl, R. Catalysis Letters, 86(1-3), 33, 2003.

349. McIntyre, B. J.; Salmeron, M.; Somorjai, G. A. Science, 265, 1415, 1994.

350. Schröder, U.; McIntyre, B. J.; Salmeron, M.; Somorjai, G. A.; Surf. Sci., 331-333, 337,

1995.

351. McIntyre, B. J.; Salmeron, M.; Somorjai, G. A. Catal. Lett., 39, 5, 1996.

352. Land, T. A.; Michely, T.; Behm, R. J.; Hemminger, J. C.; Comsa, G. J. Chem. Phys., 97,

6774, 1992.

353. McIntyre, B. J.; Salmeron, M.; Somorjai, G. A. J. Catal., 164, 184, 1996.

354. Gaigneaux, E. M.; Ruiz, P.; Wolf, E. E.; Delmon, B. J. Catal., 172, 247, 1997.

355. Occelli, M. L.; Olivier, J. P.; Auroux, A. J. Catal., 209, 385, 2002.

356. Occelli, M. L.; Gould, S. A. C. J. Catal., 198, 41, 2001.

357. Occelli, M. L.; Kalwei, M.; Wölker, A.; Eckert, H.; Auroux, A.; Gould, S. A. C. J. Catal.,

196, 134, 2000.

358. Speight, J. G. The Chemistry and Technology of Petroleum, 2nd ed; Dekker: New York,

1991.

359. Taylor, K. C. Catal. Rev. Sci. Eng., 35, 457, 1993.

360. Rodriguez, J. A.; Hrbek, J. Acc. Chem. Res., 32(9), 719, 1999.

361. Patterson, C. H.; Lambert, R. M. Surf. Sci., 187, 339, 1987.

362. Forbes, J. G.; Gellman, A. J.; Dunphy, J. C.; Salmeron, M. Surf. Sci., 279, 68, 1992.

363. Bömermann, J.; Huck, M.; Kuntze, J.; Rauch, T.; Speller, S.; Heiland, W. Surf. Sci.,

357/358, 849, 1996.

364. Speller, S.; Rauch, T.; Bömermann, J.; Borrmann, P.; Heiland, W. Surf. Sci., 441, 107,

1999.

365. Speller, S.; Rauch, T; Postnikov, A.; Heiland, W. Phys. Rev., B, 61(11), 7297, 2000.

366. Bürgler, D.; Tarrach, G.; Schaub, T.; Wiesendanger, R.; Güntherodt, H. J. Phys. Rev. B,

47(15), 9963, 1993.

367. Zaera, F.; Salmeron, M. Langmuir, 14, 1312, 1998.

368. Alemozafar, A. R.; Guo, X. C.; Madix, R. J.; Hartmann, N.; Wang J. Surf. Sci., 504, 223,

2002.

369. Alemozafar, A. R.; Guo, X. C.; Madix, R. J. Surface Science, 524(1-3), L84, 2003.

370. Rousset, S.; Gauthier, S.; Siboulet, O.; Sacks, W.; Belin, M.; Klein, J. Phys. Rev. Lett.,

63(12), 1265, 1989.

371. Ruan, L.; Stensgaard, I.; Besenbacher, F.; Laegsgaard, E. Ultramicroscopy, 42-44(Pt. A),

498, 1992.

372. Ruan, L.; Stensgaard, I.; Besenbacher, F.; Laegsgaard, E. J. Vac. Sci. Technol., B, 12(3),

1772, 1994.

373. Weissenrieder, J.; Göthelid, M.; Le Lay, G.; Karlsson, U. O. Surf. Sci., 515, 135, 2002.

374. Hartmann, N.; Biener, J.; Madix, R. J. Surf. Sci., 505, 81, 2002.

375. Hebenstreit, E. L. D.; Hebenstreit, W.; Diebold, U. Surf. Sci., 461, 87, 2000.

376. Hebenstreit, E. L. D.; Hebenstreit, W.; Diebold, U. Surf. Sci., 470, 347, 2001.

377. Chander, M.; Goetsch, D. A.; Aldao, C. M.; Weaver, J. H. Phys. Rev., B, 52(11), 8288,

1995.

378. Okada, H.; Inagaki, K.; Goto, H.; Endo, K.; Hirose, K.; Mori, Y. Surf. Sci., 515, 287,

2002.

379. Nakayama, K.; Aldao, C. M.; Weaver, J. H. Phys. Rev. B, 59(24), 15893, 1999.

380. Schott, J. H.; White, H. S. Langmuir, 10(2), 486, 1994.

381. Andryushechkin, B. V.; Eltsov, K. N.; Shevlyuga, V. M. Physics of Low-Dimensional

Structures, 11-2: 43, 2001.

382. Haiss, W.; Sass, J. K.; Gao, X.; Weaver, M. J. Surf. Sci., 274, L593, 1992.

383. Tao, N. J.; Lindsay, S. M. J. Phys. Chem., 96, 5213, 1992.

384. Gao, X. P.; Weaver, M. J. J. Amer. Chem. Soc., 114, 8544, 1992.

385. Sugita, S.; Abe, T.; Itaya, K. J. Phys. Chem., 97, 8780, 1993.

386. Batina, N.; Yamada, T.; Itaya, K. Langmuir, 11, 4568, 1995.

387. Yamada, T.; Batina, N.; Itaya, K. J. Phys. Chem., 99, 8817, 1995.

388. Yamada, T.; Batina, N.; Itaya, K. Surf. Sci., 335, 204, 1995.

389. Gao, X. P.; Edens, G. J.; Liu, F. C.; Hamelin, A.; Weaver, M. J. J. Phys. Chem., 98, 8086,

1994.

390. Cuesta, A.; Kolb, D. M. Surf. Sci., 465(3), 310, 2000.

391. Endo, O.; Kondoh, H.; Ohta, T., Surf. Sci., 441(2-3), L924, 1999.

392. Nakakura, C. Y.; Altman, E. I., Surf. Sci., 416(3), 488, 1998.

393. Nakakura, C. Y.; Altman, E. I., Surf. Sci., 398(3), 281, 1998.

394. Nakakura, C. Y.; Zheng, G.; Altman, E. I., Surf. Sci., 401(2), 173, 1998.

395. Andryushechkin, B. V.; Eltsov, K. N.; Shevlyuga, V. M. Surf. Sci., 472, 80, 2001.

396. Andryushechkin, B. V.; Eltsov, K. N.; Shevlyuga, V. M.; Bardi, U.; Cortigiani, B. Surf.

Sci., 497(1-3), 59, 2002.

397. Quate, C. F. Surf. Sci., 299-300, 980, 1994.

398. van Loenen, E. J.; Dijkkamp, D.; Hoeven, A. J.; Lenssinck, J. M.; Dieleman, J.; Appl.

Phys. Lett., 55(13), 1312, 1989.

399. Roberts, C. J.; Wilkins, M. J.; Beamson, G.; Davies, M. C.; Jackson, D. E.; Scholes, P. D.;

Tendler, S. J. B.; Williams, P. M. Nanotechnology, 3, 98, 1992.

400. Sumomogi, T.; Endo, T.; Kuwahara, K.; Kaneko, R.; Miyamoto, T. J. Vac. Sci. Technol.,

B, 12(3), 1876, 1994.

401. Sumomogi, T.; Endo, T.; Kuwahara, K.; Kaneko, R. J. Vac. Sci. Technol., B, 13(3), 1257,

1995.

402. Göbel, H.; von Blanckenhagen, P. J. Vac. Sci. Technol., B, 13(3), 1247, 1995.

403. Silva, L. A.; Laitenberger, P.; Palmer, R. E. J. Vac. Sci. Technol., B, 11(6), 1992, 1993.

404. Wendel, M.; Kühn, S.; Lorenz, H.; Kotthaus, J. P.; Holland, M. Appl. Phys. Lett., 65(14),

1775, 1994.

405. Wendel, M.; Lorenz, H.; Kotthaus, J. P. Appl. Phys. Lett., 67(25), 3732, 1995.

406. Goto, K.; Hane, K. Rev. Sci. Instrum., 67(2), 397, 1996.

407. Nyffenegger, R. M.; Penner, R. M. Chem. Rev., 97, 1195, 1997.

408. Anoikin, E. V.; Yang, M. M.; Chao, J. L.; Elings, J. R.; Brown, D. W. J. Vac. Sci.

Technol., A, 16(3), 1741, 1998.

409. Han, Y. C.; Schmitt, S.; Friedrich, K. Applied Composite Materials, 6, 1, 1999.

410. Kunze, U.; Klehn, B. Adv. Mater., 11(17), 1473, 1999.

411. Wiesauer, K.; Springholz, G. J. Appl. Phys., 88(12), 7289, 2000.

412. Iwata, F.; Matsumoto, T.; Sasaki, A. Nanotechnology, 11, 10, 2000.

413. Heyde, M.; Rademann, K.; Cappella, B.; Geuss, M.; Sturm, H.; Spangenberg, T.; Niehus,

H. Rev. Sci. Instrum., 72(1), 136, 2001.

414. Kato, Z.; Sakairi, M.; Takahashi, H. J. Electrochem. Soc., 148(12), C790, 2001.

415. Regul, J.; Keyser, U. F.; Paesler, M.; Hohls, F.; Zeitler, U.; Haug, R. J.; Malave, A.;

Oesterschulze, E.; Reuter, D.; Wieck, A. D. Appl. Phys. Lett., 81(11), 2023, 2002.

416. Rosa, J. C.; Wendel, M.; Lorenz, H.; Kottaus, J. P.; Thomas, M.; Kroemer, H. Appl. Phys.

Lett., 73(18), 2684, 1998.

417. Schumacher, H. W.; Keyser, U. F.; Zeitler, U.; Haug, R. J.; Eberl, K. Appl. Phys. Letts.,

75(8), 1107, 1999.

418. Hyon, C. K.; Choi, S. C.; Hwang, S. W.; Ahn, D.; Kim, Y.; Kim, E. K. Appl. Phys. Lett.,

75(2), 292, 1999.

419. Fang, T. H.; Weng, C. I.; Chang, J. G. Nanotechnology, 11, 181, 2000.

420. Hyon, C. K.; Choi, S. C.; Hwang, S. W.; Ahn, D.; Kim, Y.; Kim, E. K. Jpn. J. Appl. Phys.,

38, Part 1, No. 12B, 7257, 1999.

421. Magno, R.; Bennett, B. R. Appl. Phys. Lett., 70(14), 1855, 1997.

422. Kim, Y.; Lieber, C. M. Science, 257, 375, 1992.

423. Hyon, C. K.; Choi, S. C.; Song, S. H.; Hwang, S. W.; Son, M. H.; Ahn, D.; Park, Y. J.;

Kim, E. K. Appl. Phys. Letts., 77(16), 2607, 2000.

424. Unpublished data

425. Li, L.; Chan, C.-M.; Yeung, K. L.; Li, J.-X.; Ng, K.-M.; Lei, Y. G. Macromolecules, 34

316, 2001.

426. Li, L.; Chan, C.-M.; Li, J.-X.; Ng, K.-M.; Yeung, K. L.; Weng, L.-T. Macromolecules, 32,

8240, 1999.

427. Kim, D. H.; Koo, J. Y.; Kim, J. J. Physical Review B, 68 (11), 113406, 2003.

428. Schneir, J.; Sonnenfeld, R.; Marti, O.; Hansma, P. K.; Demuth, J. E.; Hamers, R. J. J.

Appl. Phys., 63(3), 717, 1988.

429. Gimzewski, J. K.; Möller, R. Phys. Rev. B, 36(2), 1284, 1987.

430. Hodel, U.; Memmert, U.; Hartmann, U. Phys. Rev. B, 54(24), 17888, 1996.

431. Lebreton, C.; Wang, Z. Z. Appl. Phys. A. 66, S777, 1998.

432. York, S. M.; Leibsle, F. M. Appl. Phys. Letts., 78(18), 2763, 2001.

433. Kim, J.; Uchida, H.; Yoshida, K.; Kim, H.; Nishimura, K.; Inoue, M. Japanese Journal of

Applied Physics, Part 1, 42(6A), 3616, 2003.

434. Mamin, H. J.; Chiang, S.; Birk, H.; Guethner, P. H.; Rugar, D. J. Vac. Sci. Technol. B,

9(2), 1398, 1991.

435. Fujita, D.; Jiang, Q.; Nejoh, H. J. Vac. Sci. Technol. B. 14(6), 3413, 1996.

436. Houel, A.; Tonneau, D.; Bonnail, N.; Dallaporta, H.; Safarov, V. I. Journal of Vacuum

Science & Technology, B: 20(6), 2337, 2002.

437. Becker, R. S.; Higashi, G. S.; Chabal, Y. J.; Becker, A. J. Phys. Rev. Lett., 65(15), 1917,

1990.

438. Shen, T.-C.; Wang, C.; Abeln, G. C.; Tucker, J. R.; Lyding, J. W.; Avouris, Ph.; Walkup,

R. E. Science, 268, 1590, 1995.

439. Stokbro, K.; Thirstrup, C.; Sakurai, M.; Quaade, U.; Hu, B. Y.-K.; Perez-Murano, F.;

Grey, F. Phys. Rev. Lett., 80(12), 2618, 1998.

440. Maeda, K.; Nakamura, Y. Surface Science, 528(1-3), 110, 2003.

441. Nakayama, Koji S.; Graugnard, E.; Weaver, J. H. Physical Review Letters, 89(26),

266106/1, 2002.

442. Nakamura, Y.; Mera, Y.; Maeda, K. Surface Science, 531 (1), 68, 2003.

443. Dagata, J. A.; Schneir, J.; Harary, H. H.; Evans, C. J.; Postek, M. T.; Bennett, J. Appl.

Phys. Lett., 56(20), 2001, 1990.

444. Avouris, P.; Hertel, T.; Martel, R. Appl. Phys. Lett., 71(2), 285, 1997.

445. Bloeβ, H.; Staikov, G.; Schultze, J. W. Electrochimica Acta, 47, 335, 2001.

446. Ma, Y. R.; Yu, C.; Yao, Y. D.; Liou, Y.; Lee, S. F. Phys. Rev. B, 64, art. no. 195324,

2001.

447. Snow, E. S.; Campbell, P. M. Appl. Phys. Lett., 64, 1932, 1994.

448. Nagahara, L. A.; Thundat, T.; Lindsay, S. M. Appl. Phys. Lett., 57, 270, 1990.

449. Garcia, R.; Calleja, M.; Petez-Murano, F. Appl. Phys. Lett., 72, 2295, 1998.

450. Day, H. C.; Allee, D. R. Appl. Phys. Lett., 62, 2691, 1993.

451. Shirakashi, J.; Ishii, M.; Matsumoto, K.; Miura, N.; Konagai, M. Jpn. J. Appl. Phys., Part

2, 35, L1524, 1996.

452. Shirakashi, J.; Matsumoto, K.; Miura, N.; Konagai, M. Jpn. J. Appl. Phys., Part 2, 36,

L1257, 1997.

453. Snow, E. S.; Campbell, P. M.; Rendell, R. W.; Buot, F. A.; Park, D.; Marrian, C. R. K.;

Magno, R. Appl. Phys. Lett., 72(23), 3071, 1998.

454. Snow, E. S.; Park, D.; Campbell, P. M. Appl. Phys. Lett., 69(2), 269, 1996.

455. Davis, Z. J.; Abadal, G.; Hansen, O.; Borise, X.; Barniol, N.; Perez-Murano, F.; Boisen,

A. Ultramicroscopy, 97 (1-4): 467, 2003.

456. Snow, E. S.; Campbell, P. M. Science, 270, 1639, 1995.

457. Sugimura, H.; Uchida, T.; Kitamura, N.; Masuhara, H. Appl. Phys. Lett., 63, 1288, 1993.

458. Sugimura, H.; Uchida, T.; Kitamura, N.; Masuhara, H. Jpn. J. Appl. Phys., Part 2, 32,

L553, 1993.

459. Irmer, B.; Kehrle, M.; Lorenz, H.; Kotthaus, J. P. Appl. Phys. Lett., 71, 1733, 1997.

460. Gwo, S.; Yeh, C. L.; Chen, P. F.; Chou, Y. C.; Chen, T. T.; Chao, T. S.; Hu, S. F.; Huang,

T. Y. Appl. Phys. Lett., 74(8), 1090, 1999.

461. Farkas, N.; Zhang, G.; Evans, E. A.; Ramsier, R. D.; Dagata, J. A. Journal of Vacuum

Science & Technology A, 21 (4), 1188, 2003.

462. Snow, E. S.; Campbell, P. M.; Perkins, F. K. Appl. Phys. Lett., 75(10), 1476, 1999.

463. Chien, F. S. S.; Chang, J. W.; Lin, S. W.; Chou, Y. C.; Chen, T. T.; Gwo, S.; Chao, T. S.;

Hsieh, W. F. Appl. Phys. Lett., 76, 360, 2000.

464. Chien, F. S. S.; Chou, Y. C.; Chen, T. T.; Hsieh, W. F.; Chao, T. S.; Gwo, S. J. Appl.

Phys., 89, 2465, 2001.

465. Dagata, J. A.; Tseng, W.; Bennett, J.; Schneir, J.; Harary, H. H. J. Appl. Phys., 70(7),

3661, 1991.

466. Tachiki, M.; Seo, H.; Banno, T.; Sumikawa, Y.; Umezawa, H.; Kawarada, H. Appl. Phys.

Lett., 81(15), 2854, 2002.

467. Tachiki, M.; Fukuda, T.; Sugata, K.; Seo, H.; Umezawa, H.; Kawarada, H. Jpn. J. Appl.

Phys., Part 1, 7B, 39, 4631, 2000.

468. Chien, F. S. S.; Hsieh, W. F.; Gwo, S.; Vladar, A. E.; Dagata, J. A. J. Appl. Phys., 91(12),

10044, 2002.

469. Gwo, S. J. Phys. Chem. Solids, 62, 1673, 2001.

470. Chien, F. S. S.; Wu, C. L.; Chou, Y. C.; Chen, T. T.; Gwo, S.; Hsieh, W. F. Appl. Phys.

Lett., 75(16), 2429, 1999.

471. Lüscher, S.; Fuhrer, A.; Held, R.; Heinzel, T.; Ensslin, K.; Wegscheider, W. Appl. Phys.

Lett., 75(16), 2452, 1999.

472. Heinzel, T.; Held, R.; Lüscher, S.; Ensslin, K.; Wegscheider, W. Physica, E, 7(3-4), 860,

2000.

473. Heinzel, T.; Held, R.; Lüscher, S.; Ensslin, K.; Wegscheider, W.; Bichler, M. Physica, E,

9(1), 84, 2001.

474. Keyser, U. F.; Schumacher, H. W.; Zeitler, U.; Haug, R. J.; Eberl, K. Physica Status Solidi

B-Basic Research, 224(3), 681, 2001.

475. Lüscher, S.; Held, R.; Fuhrer, A.; Heinzel, T.; Ensslin, K.; Bichler, M.; Wegscheider, W.

Materials Science & Engineering C-Biomimetic and Supramolecular Systems, 15(1-2),

153, 2001.

476. Faucher, M.; Fournier, T.; Pannetier, B.; Thirion, C.; Wernsdorfer, W.; Villegier, J. C.;

Bouchiat, V. Physica C, 368, 211, 2002.

477. Bouchiat, V.; Faucher, M.; Thirion, C.; Wernsdorfer, W.; Fournier, T.; Pannetier, B.;

Appl. Phys. Lett., 79(1), 123, 2001.

478. Curson, N. J.; Nemutudi, R.; Appleyard, N. J.; Pepper, M.; Ritchie, D. A.; Jones, G. A. C.

Appl. Phys. Lett., 78(22), 3466, 2001.

479. Held, R.; Lüscher, S.; Heinzel, T.; Ensslin, K.; Wegscheider, W. Appl. Phys. Lett., 75(8),

1134, 1999.

480. Held, R.; Heinzel, T.; Studerus, P.; Ensslin, K. Appl. Phys. Lett., 71(18), 2689, 1997.

481. Lüscher, S.; Fuhrer, A.; Held, R.; Heinzel, T.; Ensslin, K.; Bichler, M.; Wegscheider, W.

Microelectronics Journal, 33, 319, 2002.

482. Bo, X. Z.; Rokhinson, L. P.; Yin, H. Z.; Tsui, D. C.; Sturm, J. C. Appl. Phys. Lett., 81(17),

3263, 2002.

483. Held, R.; Vancura, T.; Heinzel, T.; Ensslin, K.; Holland, M.; Wegscheider, W. Appl. Phys.

Lett., 73(2), 262, 1998.

484. Matsumoto, K.; Gotoh, Y.; Maeda, T.; Dagata, J. A.; Harris, J. S. Appl. Phys. Lett., 76(2),

239, 2000.

485. Matsumoto, K.; Ishii, M.; Segawa, K.; Oka, Y.; Vartanian, B. J.; Harris, J. S. Appl. Phys.

Lett., 68, 34, 1996.

486. Minne, S. C.; Soh, H. T.; Flueckiger, Ph.; Quate, C. F. Appl. Phys. Lett., 66, 703, 1995.

487. Kuramochi, H.; Ando, K.; Yokoyama, H. Surface Science, 542 (1-2), 56, 2003.

488. Dagata, J. A.; Inoue, T.; Itoh, J.; Matsumoto, K.; Yokoyama, H. J. Appl. Phys., 84(12),

6891, 1998.

489. Snow, E. S.; Jernigan, G. G.; Campbell, P. M. Appl. Phys. Lett., 76(13), 1782, 2000.

490. Marchi, F.; Bouchiat, V.; Dallaporta, H.; Safarov, V.; Tonneau, D.; Doppelt, P. J. Vac.

Sci. Technol., B, 16(6), 2952, 1998.

491. Teuschler, T.; Mahr, K.; Miyazaki, S.; Hundhausen, M.; Ley, L. Appl. Phys. Lett., 67(21),

3144, 1995.

492. Kuramochi, H.; Ando, K.; Yokoyama, H. Japanese Journal of Applied Physics Part 1, 42

(9A), 5892, 2003.

493. García, R.; Calleja, M.; Rohrer, H. J. Appl. Phys., 86(4), 1898, 1999.

494. Calleja, M.; García, R. Appl. Phys. Lett., 76(23), 3427, 2000.

495. Tello, M.; García, R. Appl. Phys. Lett., 79(3), 424, 2001.

496. Müller, W. T.; Klein, D. L.; Lee, T.; Clark, J.; McEuen, P. L.; Schultz, P. G. Science, 268,

(5208), 272, 1995.

497. Blackledge, C.; Engebretson, D. A.; McDonald, J. D. Langmuir, 16, 8317, 2000.

498. Blasdel, L. K.; Banerjee, S.; Wong, S. S. Langmuir, 18, 5055, 2002.

499. Díaz, D. J.; Hudson, J. E.; Storrier, G. D.; Abruña, H. D.; Sundararajan, N.; Ober, C. K.

Langmuir, 17, 5932, 2001.

500. Silver, R. M.; Ehrichs, E. E.; De Lozanne, A. L. Appl. Phys. Lett., 51(4), 247, 1987.

501. Dujardin, G.; Walkup, R. E.; Avouris, Ph. Science, 255, 1232, 1992.

502. Rauscher, H.; Memmert, U.; Behm, R. J. J. Vac. Sci. Technol., B, 13(3), 1216, 1995.

503. Hong, S. H.; Zhu, J.; Mirkin, C. A. Science, 286, 523, 1999.

504. Piner, R. D.; Zhu, J.; Xu, F.; Hong, S. H.; Mirkin, C. A. Science, 283, 661, 1999.

505. Hong, S. H.; Mirkin, C. A. Science, 288, 1808, 2000.

506. Demers, L. M.; Ginger, D. S.; Park, S. J.; Li, Z.; Chung, S. W.; Mirkin, C. A. Science,

296, 1836, 2002.

507. Lee, K. B.; Park, S. J.; Mirkin, C. A.; Smith, J. C.; Mrksich, M. Science, 295, 1702, 2002.

508. Zhang, H.; Li, Z.; Mirkin, C. A. Advanced Materials, 14(20), 1472, 2002.

509. Xu, P.; Kaplan, D. Polymer Preprints, 44(1), 948, 2003.

510. Fu, L.; Liu, X.; Zhang, Y.; Dravid, V. P.; Mirkin, C. A. Nano Letters, 3(6), 757, 2003.

511. Zhang, H.; Chung, S. W.; Mirkin, C. A. Nano Letters, 3(1), 43, 2003.

512. Lim, J. H.; Ginger, D. S.; Lee, K. B.; Heo, J.; Nam, J. M.; Mirkin, C. A. Angewandte

Chemie, International Edition, 42(20), 2309, 2003.

513. Lee, K. B.; Lim, J. H.; Mirkin, C. A. J. Amer. Chem. Soc., 125(19), 5588, 2003.

514. Rozhok, S.; Piner, R.; Mirkin, C. A. Journal of Physical Chemistry B, 107(3), 751, 2003.

515. Ivanisevic, A.; Mirkin, C. A. J. Am. Chem. Soc., 123, 7887, 2001.

516. Su, M.; Dravid, V. P. Appl. Phys. Lett., 80(23), 4434, 2002.

517. Mckendry, R.; Huck, W. T. S.; Weeks, B.; Fiorini, M.; Abell, C.; Rayment, T. Nano

Letters, 2(7), 713, 2002.

518. Noy, A.; Miller, A. E.; Klare, J. E.; Weeks, B. L.; Woods, B. W.; DeYoreo, J. J. Nano

letters, 2(2), 109, 2002.

519. Su, M.; Liu, X. G.; Li, S.Y.; Dravid, V. P.; Mirkin, C. A. J. Am. Chem. Soc., 124(8),

1560, 2002.

520. Li, Y.; Maynor, B. W.; Liu, J. J. Am. Chem. Soc., 123, 2105, 2001.

521. Maynor, B. W.; Li, Y.; Liu, J. Langmuir, 17, 2575, 2001.

522. Weeks, B. L.; Noy, A.; Miller, A. E.; De Yoreo, J. J. Phys. Rev. Lett., 88(25), art. no.

255505, 2002.

523. Sheehan, P. E.; Whitman, L. J. Phys. Rev. Lett., 88(15), art. no. 156104, 2002.

524. Jang, J.; Schatz, G. C.; Ratner, M. A. J. Chem. Phys., 116(9), 3875, 2002.

525. Schwartz, P. V. Langmuir, 18, 4041, 2002.

526. Liu, X. G.; Fu, L.; Hong, S. H.; Dravid, V. P.; Mirkin, C. A. Adv. Mater., 14(3), 231,

2002.

527. Demers, L. M.; Mirkin, C. A. Angew. Chem. Int. Ed., 40(16), 3069, 2001.

528. Demers, L. M.; Park, S. J.; Taton, T. A.; Li, Z.; Mirkin, C. A. Angew, Chem. Int. Ed.,

40(16), 3071, 2001.

529. Weinberger, D. A.; Hong, S. H.; Mirkin, C. A.; Wessels, B. W.; Higgins, T. B. Adv.

Mater., 12 (21), 1600, 2000.

530. Amro, N. A.; Xu, S.; Lu, G. Y. Langmuir, 16, 3006, 2000.

531. Ali, M. B.; Ondarçuhu, T.; Brust, M.; Joachim, C. Langmuir, 18, 872, 2002.

532. Zhang, M.; Bullen, D.; Chung, S. W.; Hong, S. H.; Ryu, K. S.; Fan, Z. F.; Mirkin, C. A.;

Liu, C. Nanotechnology, 13, 212, 2002.

533. Gimzewski, J. K.; Joachim, C. Science, 283, 1683, 1999.

534. Eigler, D. M.; Schweizer, E. K. Nature, 344, 524, 1990.

535. Crommie, M. F.; Lutz, C. P.; Eigler, D. M. Science, 262, 218, 1993.

536. Manoharan, H. C.; Lutz, C. P.; Eigler, D. M. Nature, 403, 512, 2000.

537. Lyo, I-W.; Avouris, P. Science, 253, 173, 1991.

538. Uchida, H.; Huang, D. H.; Grey, F.; Aono, M. Phys. Rev. Lett., 70(13), 2040, 1993.

539. Kobayashi, A.; Grey, F.; Williams, R. S.; Aono, M. Science, 259, 1724, 1993.

540. Chang, C. S.; Su, W. B.; Tsong, T. T. Phys. Rev. Lett., 72(4), 574, 1994.

541. Tsong, T. T. Phys. Rev., B. 44(24), 13703, 1991.

542. Kondo, S.; Heike, S.; Lutwyche, M.; Wada, Y. J. Appl. Phys., 78(1), 155, 1995.

543. Lee, H. J.; Ho, W. Science, 286, 1719, 1999.

544. Ho, W. Acc. Chem. Res., 31, 567, 1998.

545. Hla, S. W.; Rieder, K. H. Annual Review of Physical Chemistry, 54, 307, 2003.

546. Shen, T. C. Surf. Rev. Lett., 7(5-6), 683, 2000.

547. Jung, T. A.; Schlittler, R. R.; Gimzewski, J. K.; Tang, H.; Joachim, C. Science, 271, 181,

1996.

548. Cuberes, M. T.; Schlittler, R. R.; Gimzewski, J. K. Appl. Phys. Lett., 69(20), 3016, 1996.

549. Bernard, A.; Delamarche, E.; Schmid, H.; Michel, B.; Bosshard, H. R.; Biebuyck, H.

Langmuir, 14, 2225, 1998.

550. Bishop, A. R.; Nuzzo, R. G. Curr. Opin. Colloid Interface Sci., 1, 127, 1996.

551. Chwang, A. B.; Granstrom, E. L.; Frisbie, C. D. Adv. Mater., 12(4), 285, 2000.

552. Liu, G. Y.; Xu, S.; Qian, Y. Acc. Chem. Res., 33, 457, 2000.

553. Xu, S.; Liu, G. Y. Langmuir, 13, 127, 1997.

554. Xu, S.; Miller, S.; Laibinis, P. E.; Liu, G. Y. Langmuir, 15, 7244, 1999.

555. Liu, J. F.; Cruchon-Dupeyrat, S.; Garno, J. C.; Frommer, J.; Liu, G. Y. Nano Letters, 2(9),

937, 2002.

556. Kenseth, J. R.; Harnisch, J. A.; Jones, V. W.; Porter, M. D. Langmuir, 17(13), 4105, 2001.

557. Xu, S.; Amro, N. A.; Liu, G. Y. Appl. Surf. Sci., 175, 649, 2001.

558. Wadu-Mesthrige, K.; Xu, S.; Amro, N. A.; Liu, G. Y. Langmuir, 15(25), 8580, 1999.

559. Chen, J. S.; Cousty, J.; Charlier, J.; Lecayon, G. langmuir, 12(13), 3252, 1996.

560. Liu, M. Z.; Amro, N. A.; Chow, C. S.; Liu, G. Y. Nano Lett., 2(8), 863, 2002.

561. Brower, T. L.; Garno, J. C.; Ulman, A.; Liu, G. Y.; Yan, C.; Golzhauser, A.; Grunze, M.

Langmuir, 18(16), 6207, 2002.

562. Schwartz, P. V. Langmuir, 17(19), 5971, 2001.

563. Garno, J. C.; Yang, Y. Y.; Amro, N. A.; Cruchon-Dupeyrat, S.; Chen, S. W.; Liu, G. Y.

Nano letters, 3 (3), 389, 2003.

564. Case, M. A.; McLendon, G. L.; Hu, Y.; Vanderlick, T. K.; Scoles, G. Nano letters, 3 (4):

425, 2003.

565. Wang, X. Z.; Zhou, D. J.; Rayment, T.; Abell, C.

Chemical Communications, (4), 474, 2003.

566. Brandow, S. L.; Dressick, W. J.; Dulcey, C. S.; Koloski, T. S.; Shirey, L. M.; Schmidt, J.;

Calvert, J. M. J. Vac. Sci. Technol. B, 15(5), 1818, 1997.

567. Schaefer, D. M.; Reifenberger, R.; Patil, A.; Andres, R. P. Appl. Phys. Lett., 66(8), 1012,

1995.

568. Junno, T.; Carlsson, S. B.; Xu, H. Q.; Montelius, L.; Samuelson, L. Appl. Phys. Lett.,

72(5), 548, 1998.

569. Junno, T.; Deppert, K.; Montelius, L.; Samuelson, L. Appl. Phys. Lett., 66(26), 3627,

1995.

570. Sheehan, P.; Lieber, C. M. Science, 272, 1158, 1996.

571. Baumeister, B.; Jung, T. A.; Meyer, E. Appl. Phys. Lett., 78(17), 2485, 2001.

572. Park, K. H.; Ha, J. S.; Yun, W. S.; Ko, Y. J. Jpn. J. Appl. Phys., 39, Part 1, (7B), 4629,

2000.

573. Park, K. H.; Ha, J. S.; Yun, W. S.; Lee, E-H. J. Vac. Sci. Technol., A, 17(4), 1441, 1999.

574. Hudson, J. E.; Abruña, H. D. J. Am. Chem. Soc., 118, 6303, 1996.

575. Avouris, Ph.; Wolkow, R. Phys. Rev. B, 34, 5091, 1989.

576. Smith, D. P. E.; Kirk, M. D.; Quate, C. F. J. Chem. Phys. 86, 6034, 1987.

577. Avouris, Ph.; Lyo, I.-W.; Bozso, F. J. Vac. Sci. Technol. B, 9, 424, 1991.

578. Feenstra, R. M.; Stroscio, J. A.; Tersoff, J.; Fein, A. P. Phys. Rev. Lett. 58, 1192, 1987.

579. Schmid, M.; Varga, P. in Woodruff, D. D. (ed.), The chemical physics of solid surfaces,

vol. 10: Surface alloys and alloy surfaces, Elsevier: Amsterdam, 2002.

Table 1. Some catalytic metal surfaces imaged by STM

Metal Method Reference

Al (111) UHV –STM 28, 29, 30

Ag (110) high temperature STM,

UHV-STM, high-performance UHV-mode FI (field ion)-STM

31, 32, 33, 34, 35, 36

Ag (111) Variable temperature UHV-STM

37

Ag (111) thin films on cleaved pyrolytic graphite

STM in air 38

Ag (115) high-speed, high temperature, UHV-STM

39

Au (100) pseudohexagonal (5×27) surface

low temperature UHV-STM 40

Au (110) high temperature STM, UHV-STM, UHV-pocket-size-type-STM, RHEED (reflection high energy electron diffraction)

31, 32, 41, 42, 43, 44

Au (111) STM in air, UHV-STM, STM/STS (scanning tunneling spectroscopy)

45, 46, 47, 48, 49, 50, 51

Au (433) UHV-STM 52

Au (991) UHV-STM, LEED (low energy electron diffraction)

53

Au (111), Au (110) thin films on cleaved pyrolytic graphite

STM in air 38

Polycrystalline Au film vacuum deposited on HOPG (highly oriented pyrolytic graphite)

UHV-STM 48

Cu (100) UHV-STM at room temperature

54, 55, 56, 57

Cu (110) UHV-pocket-size-type STM

41

Cu (111) UHV-STM, STM/STS 47, 58, 59

Cu (11n) n=3,5,9 UHV beetle-type-STM at room temperature

60

Cu (111) thin film on cleaved pyrolytic graphite

STM in air 38

Cr (001) STM/STS at room temperature

61, 62

Fe (001) UHV-STM/STS at room temperature

62, 63

Fe (100) UHV-STM 64

Fe (110) UHV-STM at room temperature

65

Gallium single crystal UHV-STM 48

Ir (110) Variable-temperature UHV-STM, LEED, AES (Auger electron spectroscopy)

66, 67

Mo (100), (110), (111) STM in air 68

Pb (110), Pb (111) UHV-STM 69

Polycrystalline palladium (001), (110) and (111) planes

UHV-STM 70

Pt (110) high temperature STM, UHV-pocket-size-STM

31, 43

Pt (111) UHV-STM 71

Ta (110) UHV-STM 65

V (001) UHV-STM/STS 72, 73

W (100) low temperature UHV-STM, STM in air

68, 74

W (110) UHV-STM, STM in air 65, 68

W (111) STM in air 68

W (112) UHV-STM 75

Table 2. Some metal oxide surfaces imaged by STM and AFM

Materials Method Reference

Al2O3 on Re (0001) STM 78

CeO2 (111) noncontact AFM 79

CoO (001) high temperature STM 80

CoO high temperature STM 81

Oxidized cobalt particles on graphite.

STM, XPS 82

α-Fe2O3 (0001) STM 83, 84

α-Fe2O3 (001) hematite surfaces

STM 85

Fe3O4 (001) STM 86

Fe3O4 (110) STM, UHV-STM, LEED 87, 88

Fe3O4 (111) STM, LEED 89, 90

Fe3O4 (110) on MgO UHV-STM/STS 91

Fe3O4 on Si(100) STM 92

MgO on Ag (001) STM 93

Mg(0001) oxidation STM, electron stimulated desorption ion angular distributions, LEED

94

NiO high temperature STM 81

NiO (001) high temperature STM 80, 95, 96

NiO (100) UHV-noncontact AFM 97

NiO (100) STM 98

NiO (100) on Ag (100) STM, LEED 99

NiO (100), (111) on Au (111)

STM, LEED 100

Pd (100) oxidation In situ variable-temperature STM, TPD (temperature programmed desorption), LEED

101

RuO2 (110) STM, LEED 102

RuO2 (110) on Ru (0001)

STM 103

SnO2 (110)-(4×1), (1×2) reconstructions

noncontact AFM, STM 104

TiO2 (100) noncontact AFM 105

TiO2 anatase (100) STM 106

Rutile TiO2 (100)-(1×3). STM 107

TiO2 (110) STM/STS, variable temperature STM, LEED

108, 109, 110, 111, 112, 113, 114,115

Rutile TiO2 (110) STM 116

TiO2 (110)-(1×1) noncontact AFM 117

TiO2 STM 118

Reduced TiO2-x(110) STM/STS 119

UO2 high temperature STM 81

UO2 (111), UO2 (110), high temperature STM 95

V2O5 (001) STM 120

V2O5 (010) STM/STS 121

WO3 (001) STM 122

Monoclinic γ-WO3 (001) STM, AES, LEED 123

WO3, NaxWO3 STM 124

Table 3. Nanoclusters and nanoparticles

Cluster Substrate Method Reference

Al cluster HOPG STM 125, 127

cleaved graphite STM 126

stepped and unstepped GaAs (110)

STM 128

Si(111)-(7×7) In situ STM 129

HOPG, amorphous carbon

STM 130

Si(111) STM 131, 133

TiO2 (110) STM 132

Ag(111) clusters Si(111) √3 × √3(R30°)-Ag surface

STM 134

Ag3- clusters

(clusters are produced by sputtering)

HOPG STM 135

Ag7- clusters HOPG STM 136

Ag7+ clusters Pt (111) STM, Thermal

energy atom scattering (TEAS)

137

Ag cluster HOPG STM 125, 138, 139

cleaved graphite STM 126

Si(100) STM 140

TiO2 (110) STM, XPS 141

Sb-terminated Si STM/STS 142

Si(111)-(7×7), HOPG

STM 143,144

GaAs (110) STM 145

H-terminated Si(100)-(2×1)

STM 146

Ag cluster oriented SiO2 films on Mo(112).

STM, LEED 147

Au clusters HOPG STM 125, 130, 139, 148, 149, 150

TiO2 (110) STM 151

self-assembled alkanethiol monolayer

STM/STS 152

cleaved graphite STM 126

cleaved surfaces of natural graphite single crystals

In situ STM 153

Si(111)-(7×7), HOPG

STM 143, 144

single crystal surfaces of titania

STM/STS 154

Thin C60 film on Si(111) substrate

STM 155

HOPG, amorphous carbon films

STM 156

TiO2(001)/Mo(100) STM/STS, TPD, ISS (ion scattering spectroscopy)

157

HOPG STM, TEM 158

Au (100) STM 159

Si(111)-(7×7) STM 160

Au55 clusters (i.e., Au55[(C6H5)3P]12Cl6 and Au55[(C6H5)2PC6H4SO3Na]12Cl6)

HOPG STM 161

Au55(PPh3)12Cl6 clusters pyrolytic graphite STM 162

Ligand stabilized A (PPh ) Cl

Au, HOPG STM 163

Au55(PPh3)12Cl6

Gold nanocrystals HOPG, Au(111) on mica

STM/STS 164

Au55 clusters (Au55(PPh3)12Cl6), Au55(T8-OSS)12Cl6

Mica, silicon, flame annealed gold on TempaxTM glass

AFM, STM, BAM (Brewster angle microscopy)

165

Au55 (Ph2PC6H4SO3H)12Cl6 Gold on annealed TempaxTM glass

AFM, STM, LTS (local tunneling spectroscopy)

166

Gold clusters prepared by the inverse micelle method using a non-ionic [CH3(CH2)12-1(CH2CH2O)5OH] surfactant

Graphite STM 167

Cd clusters HOPG STM 143

Co cluster HOPG, silicon STM 168, 169

single crystal MoS2 STM 170

Au (111) STM 171, 172

Co nanoparticles Cu (111) STM 173

Cu6 clusters Ag (110) STM 174

Cu clusters HOPG STM 125, 175

Highly ordered S(4×4)/W(111) surface

STM, AES, LEED

176

Rutile TiO2 (110)-(1×1) surface

STM 177

Au (111) electrode STM 178

Fe clusters Silicon, HOPG STM 169

In clusters Si(111)-(7×7) In situ STM 129

Ir nanoparticles TiO2 (110)-(1×2) surface

STM 179

Mo clusters HOPG STM 180

MoS2 nanoclusters, Au(111), rutile i l l

AFM, STM, AES RHEED

181, 182

single crystal AES, RHEED

Ni clusters clean graphite STM 183

HOPG, single crystal BSCCO (Bi2Sr2CaCu2O8+y)

STM/STS 184

Pd clusters cleaved surfaces of natural graphite single crystals.

In situ STM 153

MgO(100)/Mo(100) STM/STS, TPD, ISS

157

Graphite STM/STS 185

Carbon STM, HRTEM 186

HOPG STM/TEM 175, 187

HOPG STM 143, 188

Graphite, MoS2 STM 189

Pd561 (phen)38±2O200 clusters

(561 palladium atoms stabilized by phenanthrolin and O2)

Au, HOPG STM 163

Pd561(phen)38±2On pyrolytic graphite STM 162

Pd561Phen60O60X60 (X- =PF6-),

Pd561Phen60(OAc)180 clusters HOPG STM 190

Pd clusters stabilized by tetraalkylammonium salts

Quartz slides with vapor-deposited gold film

STM, HRTEM 191

Palladium complex HOPG In situ STM, XPS, cyclic voltammetry

192

Pt3- clusters

(clusters are produced by sputtering)

HOPG STM 135

Pt clusters Graphite STM 183, 193

HOPG STM 188, 194, 195, 196, 197, 198

TiO2(001)-(1×4) STM 199

Platinum nanoparticles Oxide substrates (silica, alumina and titania)

STM, vibrational spectroscopy by sum frequency generation (SFG)

200,201

Pt309Phen36O30 Au(111) STM/STS 202

Platinum carbonyl clusters [NEt4]2[Pt12(CO)24]

HOPG In situ STM 203

Hydrogenated Si cluster Si(111)-(7×7) STM 204

ZnS nanoparticles HOPG STM 205

Table 4. Surface adsorbed molecules

Substrate Adsorbate Surface structure Method References

Al (111) Oxygen (1) small islands of adsorbed O, (2) hexagonal nuclei obtained from annealing a dilute O adlayer.

STM 256

Al (111) Oxygen At 300 K, oxygen chemisorbed as (1) randomly adsorbed oxygen adatoms, (2) small (1×1) O islands consisting of only a few adatoms.

pocket-size-UHV-STM

257

Ag (110) Benzene T = 66 K: Benzene adsorbed on [1 0] step edge and kink sites located at the end of the silver close-packed atomic rows.

T = 30 K: Benzene chemisorbed on terrace sites

T = 35 K: Benzene formed striped overlayer structure running along the <001> direction commensurate with the substrate. Line dislocations gave the stripes a mean width of 3.5 nm.

T = 4 K: Benzenes appeared as protrusions and are mobile along the <001> direction. A densely packed hexa-gonal overlayer structure was formed at monolayer coverage.

low temperatureUHV-STM

258

Ag (110) Oxygen Atomic oxygen was mobile on the Ag surface at room temperature until captured

Field ion- STM (FI-STM)

259

to form a Ag-O-Ag linear chain along the <001> direction. A new type of oxygen adsorption exists over the Ag-O-Ag linear chains with much weaker bond to the Ag substrate.

Ag (110) Oxygen One-dimensional linear chains along the <001> direction, perpendicular to the Ag atom rows.

UHV-FI-STM/STS

260

Ag (110)-(1×1)

Oxygen Adsorbed oxygen formed added rows and extra lines.

FI-STM, HREELS

261

Ag (110) Oxygen Oxygen molecules were highly mobile until trapped by collision to form pairs or short strings of molecules along the troughs of the Ag(110).

low temperature UHV-STM

262

Au (110) C60, C70 disordered domain. STM 263

Au (110), Au (111)

C60, C70 Ordered hexagonal C60 overlayer.

In situ STM 264

Au (111) C60, C70 Hexagonal close-packed domain.

STM 263

Epitaxial Au (111) films on mica

C60 Isolated C60 molecules within a hexagonally ordered layer of molecularly resolvable MIBK (methyl isobutyl ketone).

STM in air 265

Au (111) C60 (2×2) UHV-STM/STS at room temperature

266

Au (111) HgCl2 (√7 ×√7)R19.1°-2HgCl2 STM 267

Co

Acetylene An ordered (5×2) carbon overlayer.

UHV-STM, high-resolution core level photoemission spectroscopy, near-edge x-ray

268 (1120)

absorption fine structure (NEXAFS), LEED

Cu (100) Oxygen (2√2×√2)R45°-O UHV-STM, LEED

269

Cu (100) Nitrogen Cu (100)-c(2×2)N surface was covered with square-shaped structure with sides 52±4 Å long, running parallel to the <100> directions.

UHV-STM 270

Cu (110) Benzene Benzene adsorbed on the long bridge sites.

An Eigler-type low temperature STM

271

Cu (110) C60, oxygen C60 form islands of a disordered hexagonal overlayer that was commensurate with the substrate. C60 formed square and corrugated phase on fully saturated (2×1)-O phase.

UHV-STM at room temperature

272

Cu (110) Oxygen c(6×2)-O formed after completion of the (2×1)-O structure.

pocket-size-UHV-STM

273

Cu (110) Oxygen Chemisorbed oxygen nucleated on terraces and isolated chains grew along the <001> direction reacting with Cu atoms from step edges and terrace patches.

UHV-STM 274

Cu (110) Oxygen Nucleation and growth of Cu (110)-O(2×1) layer occurred preferentially along <001> rows.

UHV-STM 275

Cu (110) Oxygen T = 4 K: individual oxygen related feature in partially completed (2×1)-O.

low temperature UHV-STM

276

T = 77 K: these features were mobile.

Cu (111) –(1×1)

C60 C60 molecules initially segregated to the terrace edges, but form a close-packed fcc structure at near monolayer coverage. Four different (a,b,c,d) C60 adsorption geometries were identified. a and b were fcc sites, c and d had hcp structure. The only difference between a and b, c and d is the symmetry of the adsorbed C60 with respect to the substrate.

UHV-STM equipped with a room temperature filed ion microscope (FIM)

277

Cu (111) Oxygen Dark fringes along the Cu(111) step edges, dark domains within the Cu(111) terrace and rather mobile light patches on top of the Cu terraces were observed during the initial stage adsorption. Ordered (√73R5.8°×√21R-10.9°)(“44”-structure) were formed when the O/Cu(111) surface were anneal at 473-623 K. Slight disordering of this lattice structure occurred at 723 K. The “44” structure converted to “29” structure (√13R46.1°×7R21.8°) after anneal at 673K in vacuum.

UHV-STM, LEED

278

Ni (100) Oxygen p(2×2), c(2×2) UHV-STM at room temperature

279

Ni (110) Benzene Benzene adsorbed at four-fold coordinated hollow sites.

Eigler-type low temperature STM

271

Ni (110) Nitrogen p(2×3)- Ni (110)-N UHV-STM 280

Pd (110) π-bonded ethylene and ethynyl

At low coverage, π-bonded ethylene molecules formed one-dimensional (3 ×1) structure, while ethynyl species did not form any ordered structure.

STM 281

Pd (110) 1,3-butadiene Each C=C bonds adsorbed on the top sites of the adjacent palladium atoms along (110).

Beetle-type-UHV-STM, HREELS, NEXAFS

282

Pd (110) Pyrimidine The pyrimidine molecules were preferentially adsorbed on terraces.

UHV-STM 283

Pd (110) Water molecules

Water-induced features in a low-coverage region (~ 0.02 ML) can be classified in terms of height; namely, (A) 0.15 Å, (B) 0.3 Å, and (C) 0.55 Å. In a high-coverage region, feature C dominates and forms a local c(2×2) structure.

low temperature UHV-STM

284

Pd (111) CO (√3×√3)R30°, c(4×2)-2CO, (2×2)-3CO, symmetric and lower symmetric (2×2), and several other intermediate coverage structures.

variable temperature UHV-STM

285

Pd (111) NO Ordered c(4×2), c(8×2), and p(2×2) structures.

variable temperature UHV-STM, density functional theory (DFT)

286

Pt (110) Oxygen Oxygen appears as bright protrusions on the ridges of the "missing row" reconstructed surface.

UHV-STM, DFT

287

Pt (111) C2H2 At high C2H2 coverage and T = 120 K: (2 ×2)

UHV-STM 288

structure,

At high C2H2 coverage and T = 220 K: (2 ×2) structure separated by bright lines,

At high C2H2 coverage and T = 370 K: (2 ×2) structure appeared with bright protrusions,

At low C2H2 coverage and T = 120 K: random features,

At low C2H2 coverage and T = 220 K: (2 ×2) islands.

Pt (111) H2O Depending on the preparation conditions the bilayer exhibited three different phases.

Phase (I) was characterized as an ideal ice bilayer rotated +/-7 degrees with respect to the <112>-direction of the Pt(111)-surface.

Phase (IIb) was less dense than phase (I) and appeared as ordered domains of H2O-molecules with the (√ 3×√ 3)R30º -distance of the Pt(111).

Phase (IIa) had a super structure with the same periodicity as phase (IIb), but with a different orientation.

variable temperature STM.

289

Pt (111) NO Ordered (2×2) structure. Two different NO species denoted as α and β were identified. The β species appeared to be higher than α species.

low temperature UHV-STM, HREELS, IRAS (infrared absorption spectroscopy)

290

Pt (111) Xe Hexagonal incommensurate rotated (HIR) phase.

variable-temperature STM

291

Ru (0001) NO N and O form a dense intermixed 2×2 phase in equilibrium with a dilute lattice gas.

UHV-STM 292

Ru (0001) Oxygen T < 130 K: dense, disordered islands partly with a (1×1) configuration,

160 < T < 170 K: onset of diffusion of chemisorbed oxygen atoms,

T > 210 K: formation of (2 ×2) and (2×1) structures.

low temperature UHV-STM

293

FIGURE 1. A 2240 Å × 2240 Å image of Au(111) displaying the characteristic (22×√3) reconstruction. This image was recorded with tunneling parameters of 0.40 V and 1.0 nA. (from ref. 208). Reprinted with permission from Langmuir, 13, 2318, 1997. Copyright (1997) American Chemical Society.

FIGURE 2. Proposed models for the TiO2(110)-(1×2) surface. Large circles represent O atoms, with Ti atoms represented by small filled circles. Both top and side views are shown. (a) The missing O-row model in which alternate bridging-O rows are removed from the stoichiometric 1×1 termination. (b) The added Ti2O3 structure proposed by Onishi et al (ref.212). Unit cells are outlined in both models. (c) Proposed model for the 1×2 phase, which consists of added rows of a fully reduced 1×1 termination. (From ref. 213). Pang, C. L.; Haycock, S. A.; Raza, H.; Murray, P. W.; Thornton, G.; Gülseren, O.; James, R.; Bullett, D. W. Phys. Rev. B, 58, 1586, 1998. Copyright (1998) by the American Physical Society.

(C)

FIGURE 3. A sequence of images taken during reoxidation of TiO2 (110)-(1×1) surface at an O2 pressure of 1.0×10-7 mbar and temperature of 723 K. All images are 750 Å × 750 Å, sample bias: +1.1 V, tunnel current 0.10 nA, constant current imaging. The total oxygen exposures for a-f were 609, 622, 654, 682, 709, and 750 L, respectively. This equates to a time interval on average of 370 s between images. Examples of the main features of the images are marked as follows: diffusing features (DF), nucleation points (NP), (1×2) strings (ST), (1×1) islands (IS), area of cross-linked (1×2) (XL). The parallel lines in e highlight the width of the depletion region adjacent to the step edge. (From ref. 216). Smith, R. D.; Bennett, R. A.; Bowker, M. Phys. Rev., B, 66, 035409, 2002. Copyright (2002) by the American Physical Society.

a b

c d

e f

FIGURE 4. Optical microscopy pictures of sol-gelprocess as a function of time. (a) 15 s, (b) 35 s,

(c) 70 s. The bar in the pictures is about 100 µm. AFM images of local morphological

transformation. (d) 5 min, (e) 15 min, (f) 42 min, (g) 193 min, (h) 365 min, (i) 680 min.

C

d

A

B

C

D

E F

H G

a b c

e

A

B

C

D

EF

H G

f

A

B

C

D

EF

H G

g

A

B

C

D

E

F

H G

h

A

B

C

D

E

F

H G

i

A

B

C

D

E

F

H G

FIGURE 5. High resolution STM images of Pt/graphite catalyst.

FIGURE 6. (a) Ex-situ 320 nm × 320 nm STM image (Vtip = +0.7V; I = 0.4 nA) showing the nucleation of 3 equivalent monolayer gold at the edges of the titania nano-crystallites. (b) A 100 nm ×100 nm UHV-STM image (Vtip = +1 V; I =1 nA) showing 0.5 equivalent monolayer freshly deposited gold. (from ref. 233). Reprinted with permission from J. Phys. Chem., B, 106, 5390, 2002. Copyright (2002) American Chemical Society.

a b

FIGURE 7. 100 nm × 100 nm STM images of Au clusters supported on TiO2 (1×1) at 450K. Clusters that moved or disappeared because of tip-cluster interactions are marked with squares; clusters that change in size are highlighted with circles. The conditions for each images are: (a) UHV; (b) Pmixture= 10-4Pa; (c) Pmixture= 1Pa; (d) Pmixture= 360Pa; total exposure (TE)∼2×109L; (e) Pmixture= 720Pa, TE∼3×1010L; (f) Pmixture= 720Pa, TE∼1.4×1011L. (From ref. 234). Reprinted from Surface Science, 490(1-2), Kolmakov, A.; Goodman, D. W. “Scanning tunneling microscopy of gold clusters on TiO2 (110): CO oxidation at elevated pressures”, L597, Copyright (2001), with permission from Elsevier.

a b

c d

e f

FIGURE 8. 500 nm × 500 nm AFM images at different stages of calcination of (a) An Au(PPh3)(NO3)-deposited TiO2(110) surface. Each image was obtained at RT after calcination of the sample (b) in the AFM chamber under 1 atm of dry air at 313 K for 30 min, (c) 363 K for 30 min, (d) 423 K for 30min, (e) 493 K for 30 min and (f) 493 K for 4 h, respectively. (A) Frequency shift images. (B) Topographic images of the square areas of (c), (d) and (f) in (A). (from ref. 238, Fukui, Ken-ichi; Sugiyama, S.; Iwasawa, Y. Phys. Chem. Chem. Phys., 3, 3871, 2001.-Reproduced by permission of The Royal Society of Chemistry on behalf of the PCCP owner Societies.)

FIGURE 9. 1000 Å × 1000 Å STM images of various Cu coverages deposited on reconstructed TiO2(110) at room temperature and annealed at 700K: (a) 0.14ML, (b)0.35ML, and (c) 0.51ML. (from ref. 241). Reprinted from Surface Science, 494(1), Reddic, J. E.; Zhou, J.; Chen, D. A. “Scanning tunneling microscopy studies of the growth of Cu clusters on a reconstructed TiO2(110)-(1×2) surface”, L767, Copyright (2001), with permission from Elsevier.

FIGURE10. (a) 300 nm × 300 nm STM image following deposition of 0.3 ML of Pd on TiO2(110) at room temperature in a single deposition step. (b) 300 nm × 300 nm STM image following deposition of 0.3 ML of Pd on TiO2(110) at 750 K in a sequence of six equal deposition steps. The image was recorded at 750 K. Note the bimodal distribution of particle sizes. Scanning conditions: tip bias -3 V, 1 nA tunnel current. (c) and (d) are 300 nm × 300 nm STM images of 0.3 ML Pd on TiO2(110) at 750 K. The Pd was deposited in a sequence of six equal deposition steps with a period of 2 h between successive depositions. Image (c) is taken 90 min after the last deposition and image (d) is taken 240 min after the last deposition i.e. there is an elapse time of 150 min between the two images. Scanning conditions: tip bias -3 V, 1 nA tunnel current. (from Ref. 245). Reprinted from Surface Science, 515(2-3), Howard, A.; Mitchell, C. E. J.; Egdell, R. G. “Real time STM observation of Ostwald ripening of Pd nanoparticles on TiO2 (110) at elevated temperature”, L504, Copyright (2002), with permission from Elsevier.

a c

b d

FIGURE 11. STM image of an anatase TiO2 (001)-(1×4) surface covered by 0.2 ML Pt after annealing in UHV at 470K. (from ref. 246). Reprinted from Surface Science, 479(1-3), Gan, S.; El-azab, A.; Liang, Y. “Formation and diffusion of Pt nanoclusters on highly corrugated anatase TiO2 (001)-(1×4) surface”, L369, Copyright (2001), with permission from Elsevier.

FIGURE 12. STM results after the high-temperature treatment. (a) 2000 Å × 2000 Å image shows clusters are approximately 200 Å wide and 40 Å high. Most clusters show hexagonal shape elongated along the substrate [001] direction (type A). A few square clusters (type B) are seen. (b) Atomic-resolution image of an encapsulated “type-A” cluster. (c) Atomic-resolution image of a square “type-B” cluster, showing an amorphous overlayer. (From ref. 247). Dulub, O.; Hebenstreit, W.; Diebold, U. Phys. Rev. Lett., 84(16), 3646, 2000. Copyright (2000) by the American Physical Society.

a

b

c

FIGURE 13. 500 nm × 500 nm AFM images of Cu(ac)2 butanol spin-coated onto oxidized Si(100) at 5000 rpm and calcinated to 450 °C at 300 °C/h for 4 h. The maximum height of the vertical scale is 10 nm for each image: (a) 0.0040 M; (b) 0.0070 M; (c) 0.0085 M; (d) 0.010 M. (from ref. 248). Reprinted with permission from Langmuir, 15, 2043, 1999. Copyright (1999) American Chemical Society.

a b

c d

FIGURE 14. STM images of H-exposed Si(111)-(7×7) surface. (a) and (b) show the hopping motion of single point defect within an unfaulted half cell when H is adsorbed on a rest-atom site. Images (c) and (d) captured the jump of a point defect from an unfaulted half-cell to a neighboring faulted half-cell. (from ref. 307). Lo, R. L.; Hwang, I. S.; Ho, M. S.; Tsong, T. T. Phys. Rev. Lett., 80(25), 5584, 1998. Copyright (1998) by the American Physical Society.

FIGURE 15. (a)-(c) Movement of a Si magic cluster within a Si(111)-(7×7) half-cell. Images were taken at 743 K at the sample bias of -2.0 V. (from ref. 315). Reprinted from Surface Science, 514(1-3), Hwang, I. S.; Ho, M. S.; Tsong, T. T. “Dynamic behavior of Si magic clusters on Si(111) surfaces”, 309, Copyright (2002), with permission from Elsevier.

FIGURE 16. Long-distance anisotropic motion of Si magic clusters on Si(111)-(7×7). These five images are chosen from continuous-time scan of 9s time interval each, taken at the sample bias of -2 V and at 723 K. The image size is 800 Å × 670 Å. The current direction is indicated at the lower-right hand corner of (a), which is in the ascending step (step-up) direction of the substrate. (from ref. 315). Reprinted from Surface Science, 514(1-3), Hwang, I. S.; Ho, M. S.; Tsong, T. T. “Dynamic behavior of Si magic clusters on Si(111) surfaces”, 309, Copyright (2002), with permission from Elsevier.

FIGURE 17. Images (14 nm × 7 nm) taken from a movie recorded by scanning tunneling microscopy, illustrating the diffusion of embedded indium atoms at room temperature. The fine corrugation is due to the atomic lattice of the Cu(001) surface. The four protrusions are individual indium atoms, each one replacing a single copper atom in the surface layer. (a) Initial surface structure at t=0 s, (b) the positions of the four indium atoms remained unchanged after 140 s, but (c) 20 s later, three of the four indium atoms made a sudden translational motion of up to 5 atomic spacings. All motion exhibited similar pattern of long waiting time followed by simultaneous displacement of several indium atoms over long distances. (from Ref. 324). Reprinted with Nature’s copyright permission. Copyright (2000).

FIGURE 18. A series of successive STM images, recorded during dosing of the O-covered Pt(111) surface with H2. (a) – (c) STM images (17 nm × 17 nm) from an experiment conducted at 131 K [P(H2)=8×10-9 mbar]. The hexagonal pattern in (a) was the (2×2)O structure; O atoms appeared as dark dots and the bright features were the OH islands. In (c), the area is mostly covered by OH, which formed ordered (√3×√3)R30° and (3×3) structures. The white, fuzzy features were H2O-covered areas. (d) – (f) STM images (220 nm × 220 nm) from an experiment conducted at 112 K [P(H2)=2×10-8 mbar]. In (d), the surface was mostly O-covered (not resolved). The bright dots were small OH islands, most of which were concentrated in the expanding ring. H2O in the interior of the ring was not resolved in the images. Thin, mostly vertical lines were the atomic steps. (from ref. 336). Reprinted (abstracted/excerpted) with permission from [Sachs, C.; Hildebrand, M.; Völkening, S.; Wintterlin, J.; Ertl, G. Science, 293, 1635, 2001.]. Copyright (2001) American Association for the Advancement of Science.

a b c

d e f

FIGURE 19. A series of STM images (180 Å × 170 Å), recorded during the reaction of adsorbed oxygen atoms with co-adsorbed CO molecules at 247 K from the same area of a Pt(111) crystal. Before the experiment, a submonolayer of oxygen atoms was prepared (by an exposure of 3 Langmuirs O2 at 96 K, a short annealing to 298 K and cooling to 247 K), and CO was continuously supplied from the gas phase (PCO=5×10-8 mbar). At this pressure, the impingement rate of CO molecules was about 1 monolayer per 100 s. The times duration was measured from the start of CO exposure. The structure at the upper left corner is an atomic step of the Pt surface. The tunneling voltage (with respect to the sample) is +0.5V and the tunneling current is 0.8 nA. (from ref. 338). Reprinted (abstracted/excerpted) with permission from [Wintterlin, J.; Völkening, S.; Janssens, T. V. W.; Zambelli, T.; Ertl, G. Science, 278, 1931, 1997.]. Copyright (1997) American Association for the Advancement of Science.

FIGURE 20. Proposed model for Pt-Rh tip catalyzed hydrogenation of coke in a hydrogen-

containing atmosphere. (from ref. 349). Reprinted (abstracted/excerpted) with permission from

[McIntyre, B. J.; Salmeron, M.; Somorjai, G. A. Science, 265, 1415, 1994.]. Copyright (1994)

American Association for the Advancement of Science.

FIGURE 21. STM image (620 Å ×100 Å) of a Pt(111) surface covered with a sulfur p(2×2) ordered overlayer. This image was acquired after a few hours following the sulfur dosing and illustrates the intermediate structures obtained during the step doubling that is induced by the adsorbed sulfur atoms. The p(2×2) pattern can be seen on the terraces and extended all the way to the bottom and top of the steps, which had somewhat rough edges but were nevertheless macroscopically aligned. (from ref. 367). Reprinted with permission from Langmuir, 14, 1312, 1998. Copyright (1998) American Chemical Society.

FIGURE 22. STM images of (a) p(2×2) iodine phase structure at θ =0.25 (115 Å × 99 Å), (b) coexisting liquid and c(6×2) iodine phases (102 Å ×102 Å), (c) coexisting c(6×2) and c(14×2) iodine phases (260 Å × 265 Å). The c(14×2) domains grew near the atomic steps. Arrows indicate the direction of the iodine lattice compression, (d) c(5×2) iodine phase structure (136 Å ×136 Å), and (e) LEED pattern c(5×2) structure shown in (d).The first-order spots belong to Cu(100) and the small spots are from the iodine superstructure. (From ref. 396). Reprinted from Surface Science, 497(1-3), Andryushechkin, B. V.; Eltsov, K. N.; Shevlyuga, V. M.; Bardi, U.; Cortigiani, B. “Structural transitions of chemisorbed iodine on Cu(100)”, 59, Copyright (2002), with permission from Elsevier.

a

b

c

d

e

AFM tip

substrate

substrate

AFM tip

substrate

AFM tip

FIGURE 23 (a) Schematic diagram of mechanical patterning process by SPM tip.

substrate

STM tip

substrate

STM tip

FIGURE 23 (b) Schematic diagram of surface melting process by SPM tip.

water bridge

AFM tip as cathode (-)

Tip induced E-field

substrate anode (+)

Tip-induced oxide V

FIGURE 23 (c) Schematic diagram of tip induced local anodic oxidation.

FIGURE 24 (a) AFM image of the patterned grooves by cantilever oscillation with feedback gains of (1) 0, (2) 3, and (3) 5. The scan speed was fixed at 0.02 µm/s. (b). AFM image of the patterned grooves with the maximum applied force at scan speeds of (1) 0.08 µm/s, (2) 0.04 µm/s, (3) 0.02 µm/s, (4) 0.008 µm/s, and (5) 0.004 µm/s. (from ref. 418). Reprinted with permission from [Hyon, C. K.; Choi, S. C.; Hwang, S. W.; Ahn, D.; Kim, Y.; Kim, E. K. Appl. Phys. Lett., 75(2), 292, 1999.]. Copyright (1999), American Institute of Physics.

a b

FIGURE 25. AFM phase images showing the influence of the AFM probe on the growth

direction of lamellar tips: (a) and (b) set point amplitude ratio of 0.72; (c) and (d) set point

amplitude ratio of 0.60; and, (e) and (f) set point amplitude ratio of 0.44.

a b

c d

0

60dee f

1 µm

1 µm

1 µm

1 µm

2 µm 2 µm

a b

c d

e f

FIGURE 26. STM images (1.4 µm × 1.4 µm) taken after writing lines at a current set point of 3 nA and a writing speed of 750 nm/min. The junction voltages were (a) 9 V, (b) 8 V, (c) 7 V, (d) 6 V, (e) 5 V, and (f) 4 V. (from ref. 430). Hodel, U.; Memmert, U.; Hartmann, U. Phys. Rev. B, 54(24), 17888, 1996. Copyright (1996) by the American Physical Society.

a b c

d e f

FIGURE 27. (a) AFM image of vertically aligned grids of oxidized lines on TiN. Local oxidation conditions: tip scanning speed 0.25 µm/s, sample bias +8 V, relative humidity 65%. (From ref. 460). Reprinted with permission from [Gwo, S.; Yeh, C. L.; Chen, P. F.; Chou, Y. C.; Chen, T. T.; Chao, T. S.; Hu, S. F.; Huang, T. Y. Appl. Phys. Lett., 74(8), 1090, 1999. ], Copyright (1999), American Institute of Physics. (b) AFM image of an array of 4864 dots. The dots are 40 nm apart with an average width of 10 nm. (From ref. 493). Reprinted with permission from [García, R.; Calleja, M.; Rohrer, H. J. Appl. Phys., 86(4), 1898, 1999.], Copyright (1999), American Institute of Physics.

a b

FIGURE 28. Scanning with a platinum-coated AFM tip over a SAM surface containing terminal

azide groups in the presence of H2 leads to the reduction of azide groups to primary amino

groups. Derivatization of the resulting amine surface with aldehyde-modified latex beads or

ATTO-TAG results in specific labeling of the reduced areas. (from ref. 496). Reprinted

(abstracted/excerpted) with permission from [Müller, W. T.; Klein, D. L.; Lee, T.; Clark, J.;

McEuen, P. L.; Schultz, P. G. Science, 268, (5208), 272, 1995.]. Copyright (1995) American

Association for the Advancement of Science.

FIGURE 29. Schematic representation of DPN process. (From ref. 504). Reprinted

(abstracted/excerpted) with permission from [Piner, R. D.; Zhu, J.; Xu, F.; Hong, S. H.; Mirkin,

C. A. Science, 283, 661, 1999.]. Copyright (1999) American Association for the Advancement of

Science.

FIGURE 30. Schematic representation of the procedure used to prepare nanostructure on a Au

substrates. (from ref. 526). Reprinted with the permission from [Liu, X. G.; Fu, L.; Hong, S. H.;

Dravid, V. P.; Mirkin, C. A. Adv. Mater., 14(3), 231, 2002.]. Copyright (2002) WILEY-VCH.

FIGURE 31. Schematic diagram showing the different steps in the formation of a single bond with the STM. (a) The tip is positioned over a single CO molecule to induce the detachment of CO from Ag and its bonding to the tip. Because CO forms a bond predominantly through the carbon, a 180° rotation of the CO occurs in the transfer. (b) The tip with the attached single CO molecule is translated (indicted by the arrow) and positioned over a Fe atom. (c) The bias voltage and the flow of electrons are reversed, inducing the transfer of CO from the tip to the Fe. (d) A single Fe–CO bond is formed. The interaction of the electric field with the dipole moment of CO may also play a role in the transfer of (a) and (c). (from ref. 543). Reprinted (abstracted/excerpted) with permission from [Lee, H. J.; Ho, W. Science, 286, 1719, 1999.]. Copyright (1999) American Association for the Advancement of Science.

a b

c d

FIGURE 32. STM image of an atomic abacus made from C60 molecules (from ref. 548). Reprinted with permission from [Cuberes, M. T.; Schlittler, R. R.; Gimzewski, J. K. Appl. Phys. Lett., 69(20), 3016, 1996.], Copyright (1996), American Institute of Physics.

FIGURE 33. Schematic diagram of four basic manipulation mechanisms using AFM (a and b) and STM (c and d). The imaging and fabrication modes are depicted in the top and bottom rows, respectively. (from ref. 552). Reprinted with permission from Acc. Chem. Res., 33, 457, 2000. Copyright (2000) American Chemical Society.

a b c d

FIGURE 34. A sequence of AFM images (670 nm × 670 nm) taken during the manipulation of a 50 nm Au particle into the gap between two Au/Ti electrodes. The height of the particles and electrodes is 30 nm. (from ref. 568). Reprinted with permission from [Junno, T.; Carlsson, S. B.; Xu, H. Q.; Montelius, L.; Samuelson, L. Appl. Phys. Lett., 72(5), 548, 1998.], Copyright (1998), American Institute of Physics.