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Applied Surface Science 311 (2014) 95–100

Contents lists available at ScienceDirect

Applied Surface Science

jou rn al h om ep age: www.elsev ier .com/ locate /apsusc

rF excimer laser-induced deposition of Ag/C nanocomposite thinlms in the presence of n-Hexane

ohammed Ashraf Gondala,∗, Radek Fajgarb, Xiaofeng Changa,b,c, Kai Shenc, Qingyu Xud

Laser Research Group, Physics Department & Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31261,audi ArabiaInstitute of Chemical Process Fundamentals, 16502 Prague, Czech RepublicCollege of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211100, PR ChinaDepartment of Physics, Southeast University, Nanjing 211189, PR China

r t i c l e i n f o

rticle history:eceived 4 February 2014eceived in revised form 19 April 2014ccepted 1 May 2014vailable online 9 May 2014

eywords:

a b s t r a c t

Ag/C nanocomposite thin films with different Ag/C molar ratios have been prepared using ArF excimerlaser-induced ablation process and silver target under n-Hexane atmosphere. The morphology, crystalstructure and composition of as-deposited Ag/C nanocomposite thin films were investigated with highresolution electronic microscopic techniques (including scanning electron microscopy and transmissionelectron microscopy) and energy-dispersive X-ray spectroscopy, respectively. Laser Raman spectroscopyand Fourier transform infrared spectroscopy techniques were also applied to characterize the final car-

rF excimer laserg/C thin filmsanocompositeaser deposition

bonaceous products generated from n-Hexane under laser ablation process. The optical emission of theplume caused by the interaction between excimer laser and silver target in the presence of n-Hexanewas studied to understand the possible reaction process. The UV–vis absorption of as-deposited Ag/Cthin films, which is attributed to the surface plasmonic excitation, was also investigated in the presentwork.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Silver nanoparticles based materials have recently gained greatignificance due to their potential applications in various fields,uch as selective heterogeneous catalysis (hydrogenation [1], oxi-ation [2]) and hydrogen storage [3]. Moreover, silver nanoparticlesre of great interest because of their surface plasmon resonanceSPR) property resulting in a strong absorption of visible light [4,5].ery recently, due to the SPR effect of silver nanoparticles, Ag/Canocomposites were reported as efficient plasmonic photocata-

ysts due to their applicability under visible light [6]. On the otherand, it is considered that such established hybrid nanostructuresre very important for biological applications due to surface func-ional groups provided by the carbonaceous products [7]. Therefore,here is a considerable interest and need for the development ofreparation technology for Ag/C nanocomposites. The thin film

reparation technique of Ag/C is also of great importance for theotential heterogeneous applications, taken into consideration theifficulty with the usage of those catalysts in the powdered form

∗ Corresponding author. Tel.: +966 138602351; fax: +966 138602293.E-mail address: magondal@kfupm.edu.sa (M.A. Gondal).

ttp://dx.doi.org/10.1016/j.apsusc.2014.05.007169-4332/© 2014 Elsevier B.V. All rights reserved.

which is hard to recycle from the aqueous solution. Hence, oneneeds to consider new methods to overcome these problems.

A series of papers have been published by our group oninfrared/excimer laser ablative deposition of nano-metals com-bined with carbonaceous products, using benzene, acetylene etc.as the carbonaceous precursor [8–11]. In our previous investiga-tions, simultaneous laser ablation of metal target in adjacent plume(dielectric breakdown) of decomposing hydrocarbon compoundscan take place thus nanometals combined with carbonaceous prod-ucts can be prepared through laser chemical vapor deposition(LCVD) approach.

In this investigation, a new preparation method has been devel-oped for the deposition of Ag/C nanocomposite thin films, via anexcimer laser induced process in the presence of n-Hexane (usedas the carbonaceous precursors). The carbonization process takesplace in dielectric breakdown of gaseous n-Hexane adjacent tosilver surface. The crystal and atomic structures of as-depositedsilver and carbon were characterized, respectively. The opticalemission spectra of the plume produced from the interaction

between excimer laser and silver target was measured in orderto understand the possible mechanism of the deposition process.Furthermore, the optical properties of as-deposited nanocompositethin films were investigated as well.

9 urface Science 311 (2014) 95–100

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6 M.A. Gondal et al. / Applied S

. Experimental

Ag/C nanocomposite were prepared in a spherical glass reac-or (diameter = 13 cm) equipped with a PTFE stopcock and a quartzindow. n-Hexane gas was used as precursor after distillation on

vacuum line. The as-prepared Ag/C nanocomposite thin film wasamed according to the preparation conditions as illustrated byAg/C-x”, and “x” (x = 20, 60 and 100) was the pressure of n-Hexaneas filled in the reactor before irradiation. The pressure was mon-tored and controlled by a pressure sensor (Edwards Barocel) andhe equipped PTFE valve, respectively. Schematic diagram of thexperimental setup for deposition is depicted in Fig. 1. The irra-iation period was 60 seconds. Amorphous glass was used as theubstrate unless otherwise specified in this paper.

The transmission electron microscopy (TEM) images includ-ng selected area electron diffraction (SAED) patterns andnergy dispersive X-ray spectroscopy (EDX) of as-depositedg/C nanocomposites were recorded using a transmission elec-

ron microscope (JSM-6510). The solid samples were transferredrom glass to Beryllium substrate before the EDX measurement.ourier transform infrared spectra (FTIR) of Ag/C nanocompos-tes deposited on polished NaCl substrates were recorded at roomemperature using a FTIR spectrophotometer (Impact 400, Thermoicolet), for the identification of the decomposition products of n-exane induced by ArF excimer laser. The decomposition products

tructure of carbon converted from n-Hexane were further charac-erized using laser Raman spectrometer (� = 473 nm, 30% of Power).he deposited solid thin films were carefully transferred to the

ungsten substrate by scratching before laser Raman spectroscopy

easurement. A spectrometer system was intergraded in the laserblation setup (as depicted in Fig. 1) to record the optical emission

Fig. 1. Schematic diagram of experimental setup for deposition of Ag/C compositethin films.

ig. 2. SEM images and corresponding EDX results (inset) of as-deposited Ag/C composite thin films prepared in the presence of n-Hexane at pressures of 20 Pa (a), 60 Pa (b)nd 100 Pa (c), respectively. Fig. 1(d) depicts the variations of C/Ag atomic % with increasing the pressure of n-Hexane.

M.A. Gondal et al. / Applied Surface Science 311 (2014) 95–100 97

Fig. 3. TEM images and the corresponding SAED patterns (inset) of as-deposited Ag/C nanocomposites in the presence of n-Hexane at pressures of 20 Pa (a), 60 Pa (b) and1 and pp

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00 Pa (c), respectively. Figures (a-1)–(c-1) and (a-2)–(c-2) show the phase results

atterns from figures (a)–(c), respectively.

OE) of plume. The optical property of as-deposited Ag/C nanocom-osite thin films (on crystalline quarts) was measured by UV-vispectrometer (Shimadzu). All the measurements were conductedwice and the average value was adopted.

. Results and discussion

The morphology of as-deposited Ag/C thin films was investi-ated using SEM and the corresponding composition analysis wasarried out as well (as depicted in Fig. 2). EDX analysis that was mea-ured on Beryllium substrate suggests the existence of carbon andilver elements. It was noticed that the pressure of n-Hexane whichas the main source of carbon, had great effect on the amount of

arbon deposited on the substrate. The product yield of carbon asell as the molar ratio of carbon to silver was found to increaseith the increase in pressure of n-Hexane up to 60 Pa and a fur-

her increase in pressure of n-Hexane could not contribute in suchmprovement, indicating that the saturation of carbon yield couldave reached by increasing the pressure of n-Hexane up to 60 Pamolar ratio of carbon to silver reaches 1.75:1). In such situation,ll the photons from the ArF excimer laser would have contributed

n the conversion of n-Hexane to carbon.

TEM and SAED were carried out to further investigate theorphology and the crystal structures of metallic silver in Ag/C

omposites deposited in the presence of n-Hexane in the 20–100 Pa

article size distributions (sample size = 50) obtained from the corresponding SAED

pressure range. As clear from Fig. 3, ball-shaped nanoparticles withthe size of 5–20 nm and relative narrow size distribution can beclearly observed from the representative TEM images of Ag/C-20and Ag/C-60. The position and relative intensity of scattering vec-tors calculated from the SAED pattern, could be well indexed as theexistence of cubic silver (JCPDS No. 04-0783), demonstrating thecubic metallic silver were deposited on the substrate after atomizedfrom the target under excimer laser irradiation.

The structure of carbonaceous products conversed from n-Hexane by ArF excimer laser was further studied by means ofRaman characterization. One can notice that only 30% of theincident laser power was utilized during the Raman spectra mea-surements, in order to prevent the unnecessary damage (oxidation)of the samples. As depicted in Fig. 4, all the Ag/C nanocompositesamples exhibit the Raman peaks centered at ∼1366 cm−1, whichcorrespond to the D band of amorphous carbon since it is quiteboard, as well as the peaks centered at ∼1585 cm− which corre-spond to the G band of graphite. Compared to the broaden D bandobserved, the G band which is caused by the first-order scatteringof the E2g mode observed from sp2 carbon domains is much sharperand has much higher Raman intensity, demonstrating the existence

of carbonaceous products with complete graphite-like structures inthe Ag/C nanocomposites [12].

The Ag/C nanocomposite thin films were directly deposited onpolished NaCl substrates under identical experimental conditions

98 M.A. Gondal et al. / Applied Surface Science 311 (2014) 95–100

3000 2500 2000 1500 1000 500

Ag/C-20 Ag/C-60 Ag/C-100

D Band

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ig. 4. Raman spectra of Ag/C nanocomposites deposited in the presence of n-exane at different pressures.

or FT-IR measurement. As depicted in Fig. 5, no peak could beistinguished from the FT-IR spectrum of Ag/C-100 sample due tohe small thickness of as-deposited sample, except the absorptiont 2360 cm−1 which is attributed to the CO2 asymmetric stretchibration (not shown). The stretching mode of C2 can be appar-ntly observed at wavenumbers of 1562 and 1593 cm−1 for theamples of Ag/C-20 and Ag/C-60, respectively [13]. Moreover, thep3 C H stretch vibration can be observed at wavenumbers cen-ered at 2861/2924/2958 cm−1 and 2918 cm−1 for the samplesf Ag/C-20 and Ag/C-60, respectively [14,15]. The FT-IR resultsre in well agreement with the Raman analysis as mentionedbove.

Fig. 6 depicts the optical emission spectra collected from thearget surface level (d = 0 cm) at a distance of 1 cm from the targeturface. It can be found that most of the lines exhibited in thesepectra could be attributed to the ionized silver. In both cases, the

ig. 6. Optical emission spectra of ionized silver plasma generated by the ArF excimer laurface in the presence of n-Hexane at different pressures of 0 Pa (a), 20 Pa (b), 60 Pa (c) a

Fig. 5. FT-IR spectra of as-deposited Ag/C nanocomposite thin films in the presenceof n-Hexane at different pressures.

strong lines centered at 519 and 545 nm are identified as the tran-sitions of 4d105p–4d105d [16]. The strongest line at around 385 nmis caused by the second harmonic from the ArF excimer laser. Fromthe optical emission spectra series measured at the surface of target,no apparent changes in the emission intensity in the UV–vis regionwere observed, in the presence of n-Hexane at different pressures.However, the negative effect of excessive n-Hexane on the emis-sion intensity detected at the distance of 10 mm from the targetcould be obviously noticed from Fig. 7. The OE intensity does notchange apparently in the presence of n-Hexane at pressure from20 Pa to 60 Pa. But nevertheless, both the optical emission intensi-ties at wavelength of 518 and 546 nm decrease almost two fold after

filling n-Hexane in the 60 to 100 Pa pressure range. The ionizationenergy values of silver atoms and the photon energy of ArF excimerlaser (� = 193 nm) were 7.57623 eV and 6.42 eV, respectively [17].

ser at the distance of 0 (left figure) and 10 mm (right figure) away from the targetnd 100 Pa (d), respectively.

M.A. Gondal et al. / Applied Surface

Fig. 7. Dependence of OE intensity detected at the distance of 10 mm away fromthe target surface in the presence of n-Hexane at different pressures.

200 300 400 50 0 60 0 700 800

λλ==525 nm

Ag/C-20 Ag/C-60 Ag/C-100

Abso

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λλ==471 nm

Fig. 8. UV–vis spectra of Ag/C composite thin films on quarts substrates depositedir

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[on carbon nanotubes and graphene raman spectroscopy, Nano Lett. 10 (2010)751–758.

n the presence of n-Hexane at pressures of 20 Pa (a), 60 Pa (b) and 100 Pa (c),espectively.

hus about 1.2 photons are needed for the ionization of one silvertom from the target, and an electron will be emitted from the tar-et as well. The lower pressure (from 20 Pa to 60 Pa) of n-Hexaneay lead to higher emission speed for electron which facilitates the

ecombination of electron and ion or atom, therefore, much thickerhin films could be obtained. On the contrast, further increase in theressure of n-Hexane (e.g. to 100 Pa) inhibits the emission speed oflectron give rise to thinner films.

It has been well known that the formation of silver particlesan be proved by UV–vis absorption measurements as silver parti-les could exhibit an intense absorption band caused by the surfacelasmonic excitation. As depicted in Fig. 8, the absorption bands inisible region suggest the fact that the silver nanoparticles are pro-uced. The absorption peak of the Ag/C composites deposited in theresence of n-Hexane at 20 Pa is centered at 519 nm. The small red-hift to 471 nm (∼50 nm of shift) can be found when increasing theressure of n-Hexane to 60 Pa (increasing the carbon/silver molaratios from 1.1 to 1.7). What’s more, the Ag/C-100 sample whichas similar molar ratio of carbon/silver with sample of Ag/C-60,xhibits similar SPR position which is centered at around 525 nm.he results mentioned above clearly suggest that the SPR position is

trongly dependent on the concentration of metal (silver nanopar-icles) in the composites, which are possibly caused by the mutualolarizations of the particles [5,18].

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Science 311 (2014) 95–100 99

4. Conclusions

In this work, Ag/C nanocomposites with uniform size distribu-tion centered at ∼10 nm were prepared in the presence of n-Hexaneusing an excimer laser induced process. Silver target and n-Hexanegas were selected as the precursor for silver and carbon atoms.The low molecular carbonaceous species were produced by simul-taneous dielectric breakdown of n-Hexane by excimer laser. Theresults clearly showed that the molar ratio of carbon to silver couldbe controlled by adjusting the n-Hexane pressure. The completegraphite-like structures, C C group and sp3 C H stretch vibra-tion were observed from Raman and FT-IR measurements. Theremarkable decrease in optical intensity of the silver plume byincreasing the pressure of n-Hexane from 60 to 100 Pa was found,which could be the main reason responsible for the much thinnerlayer deposited at pressure of 100 Pa. The dependent of SPR posi-tion (red-shift amount) on the silver nanoparticles concentrationwas also noticed and such red shift is deduced to be caused by themutual polarization of the particles.

Acknowledgements

The support under the project of National Natural Science Foun-dation of China (51172044), National Science Foundation of JiangsuProvince of China (BK2011617) and the 333 project of Jiangsuprovince is highly appreciated. M. A. Gondal is thankful to Dean-ship of Scientific Research, KFUPM for supporting this work throughproject # RG 1311-1.

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