Experimental investigation of photonic band gap influence on enhancementof Raman-scattering in metal-dielectric colloidal crystalsSriram Guddala, Shadak Alee Kamanoor, Andrea Chiappini, Maurizio Ferrari, and Narayana Rao Desai Citation: J. Appl. Phys. 112, 084303 (2012); doi: 10.1063/1.4758315 View online: http://dx.doi.org/10.1063/1.4758315 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v112/i8 Published by the American Institute of Physics. Related ArticlesMonitoring the in-situ oxide growth on uranium by ultraviolet-visible reflectance spectroscopy J. Appl. Phys. 112, 093104 (2012) Design of lumpy metallic nanoparticles for broadband and wide-angle light scattering Appl. Phys. Lett. 101, 141112 (2012) Experimental surface-enhanced Raman scattering response of two-dimensional finite arrays of gold nanopatches Appl. Phys. Lett. 101, 111606 (2012) Origins of high visible light transparency and solar heat-shielding performance in LaB6 Appl. Phys. Lett. 101, 041913 (2012) Influence of alloy inhomogeneities on the determination by Raman scattering of composition and strain inSi1–xGex/Si(001) layers J. Appl. Phys. 112, 023512 (2012) Additional information on J. Appl. Phys.Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors

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Experimental investigation of photonic band gap influence on enhancementof Raman-scattering in metal-dielectric colloidal crystals

Sriram Guddala,1 Shadak Alee Kamanoor,1 Andrea Chiappini,2 Maurizio Ferrari,2

and Narayana Rao Desai1,a)

1School of Physics, University of Hyderabad, Hyderabad 500 046, India2CNR-IFN, CSMFO Lab., Via alla Cascata 56/c, Povo, Trento 38123, Italy

(Received 23 April 2012; accepted 12 September 2012; published online 17 October 2012)

A simple chemical technique is implemented to fabricate a metal-dielectric colloidal crystal

structure (MDCS) in order to enhance the otherwise weak Raman signals by combining the

effects of localized surface plasmon resonance (LSPR) enhancement due to gold nanoparticles,

precise field confinement of dielectric and air bands in the periodic dielectric structure and field

enhancements at the photonic band gap (PBG) edges. The higher density of electromagnetic

modes (DOS) near these band edges is explained as due to the reduced group velocity at the

photonic band gap edges. Intense electric field strength due to the excitation of high DOS at the

edges of PBG of MDCS and the LSPR excitation through field confinement in the dielectric

medium of MDCS are employed to study the Raman-scattering signals of adsorbed benzenethiol

(BT) molecule on the MDCS. Large enhancement for the Raman signal in MDCS in comparison

to the Raman spectra observed for BT molecule dispersed on sputtered gold film shows the

effectiveness of MDCS for the micro-level detection of the analyte. VC 2012 American Institute ofPhysics. [http://dx.doi.org/10.1063/1.4758315]

I. INTRODUCTION

The modification in the spontaneous emission rate

owing to the location of light source in special environment

known as the Purcell effect,1 has been established as due to

the role of density of electromagnetic modes (DOS) on the

spontaneous emission of light in different mesoscopic struc-

tures viz., microcavities,2 metal-dielectric interfaces,3 dielec-

tric slabs,4 and so on. One such mesoscopic structures called

photonic crystals (PhCs), which are also called the periodic

dielectric materials,5–8 have been an interesting topic of

research to attain a complete photonic band gap (PBG),

where the propagation of electromagnetic waves of any

polarization is forbidden in any direction for some frequency

range.5 Theoretically it was predicted by Yablonovitch6 and

John7 in terms of spontaneous emission suppression and

strong Anderson localization of photons, respectively, to

demonstrate the Purcell effect in these PhCs. A theoretical

prediction was recently made by Gaponenko about the effect

of photon DOS on the spontaneous light scattering9,10 in

PhCs and its contribution to the enhancement of Raman-

scattering. As the group velocity, vg, is low for the propagat-

ing electromagnetic modes at the band edge region of the

PBG, it leads to enhanced DOS and larger light matter inter-

action as compared to a homogeneous 3D medium (Figure

1(a) in Ref. 9). There are very few reports in the literature on

the experimental results regarding the band edge DOS

effects on the Raman scattering in a PhC. Avakyants et al.11

have infiltrated NaNO2 into the silica colloidal crystal and

observed an enhancement of the NaNO2 Raman-scattering

signal under selective excitation wavelength near one of its

band edges. Another report by Kuroda et al.12 for polymer

gel infiltrated polystyrene colloidal crystal, shows the poly-

styrene Raman-scattering signal as a function of the excita-

tion frequency and an enhancement at the band edge of the

PBG. A theoretical model was also developed by Sakoda

et al.10 for such bare polystyrene opals and a possible

enhancement of the Raman-scattering due to high DOS

available at the band edge regions. The work by Mamichev

et al.13 looks at similar effects in the case of a porous silicon

multilayer 1D PhC structure. Gaponenko9 had proposed that

enhancement might be more in a metal-dielectric systems in

comparison to bare dielectric structures.

Metal-dielectric colloidal crystal structures (MDCS)

have attracted an intense research activity,14–16 during the

last decade for its unified features, localized surface plasmon

resonance (LSPR) of noble metallic nanoparticles and PBG

of colloidal type PhCs. These new optical materials have

been studied for the past few years as surface enhanced

Raman-scattering (SERS) substrates. SERS has been known

for achieving the amplification of Raman-scattering signals

of molecules in the proximity or adsorbed to noble metallic

nanoparticles or nanostructures through an intense electric

field generated because of the surface plasmon resonance

property. The general understanding of the SERS involves

two mechanisms for the enhancement of Raman-scattering:

one is electromagnetic enhancement17 and other being chem-

ical enhancement.18 The first involves the excitation of sur-

face plasmons and thereby creating high intense electric field

and the latter is due to a possible charge transfer mechanism

caused by mixing of molecular orbitals of an analyte and a

metallic structure, there by changing the environment of the

analyte.

In this communication, we are reporting the experimen-

tal observations on the possible effects of photonic band gap

in a novel MDCS. We also report the enhancement ofa)E-mail addresses: dnr.laserlab@gmail.com and dnrsp@uohyd.ernet.in.

0021-8979/2012/112(8)/084303/7/$30.00 VC 2012 American Institute of Physics112, 084303-1

JOURNAL OF APPLIED PHYSICS 112, 084303 (2012)

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Raman-scattering signal of benzenethiol (BT) molecules at

low molar concentration in MDCS and compared it with

Raman signals from BT molecules on a metallic substrate

without any photonic band gaps.

II. EXPERIMENTAL

MDCS is prepared by immobilizing the gold nanopar-

ticles (Au NPs) through a selective amino group (�NH3þ)

functionalization of the silica network in an inverse silica

opal (ISO). Scheme 1 shows the protocol followed for the

fabrication of our novel MDCS. Briefly, a bare polystyrene

(PS) opal was first grown by the vertical deposition tech-

nique.8,19 In this technique initially a 3 ml aqueous solution

of homemade mono sized 420 nm diameter PS spheres of

0.05 wt. % was taken in a 5 ml beaker. Then the hydrophi-

lized substrate was kept at 45� angle in this solution and left

at a temp of 50 �C and a relative humidity of 70%–80% for

48 h. During the process of evaporation of water the spheres

get pulled towards the meniscus due to the capillary forces

and self-assemble into a fcc crystalline lattice. Then the

structure was heat treated at 80 �C for 10 h to make the struc-

ture mechanically stable and possible necking between the

spheres. In the next step, we have infiltrated the 26% air vol-

ume fraction between the PS spheres with silica solution and

calcinated the structure at 450 �C for 30 min and then

brought it to the room temp at a ramp rate of 0.5 �C/min so

that the PS spheres get evaporated and the silica matrix gets

densified simultaneously. At the end, we will be left with a

silica matrix in the ordered original air voids and the air

voids in place of original PS spheres. This type of structure

is known as the inverse opal.8,20 This inverse structure was

functionalized with –NH3þ group by immersing it in 10%

3-aminopropyltriethoxysilane (APTES) – ethanol solution

under smooth stirring for 20 h. In the following step, the

functionalized ISO was immersed in a pre-prepared Au NPs

solution, by the well-known Turkevich method,21 for differ-

ent intervals of time: 5 h, 10 h, 15 h, and 20 h. From now

onwards the structures will be labeled as MDCS-Xh where X

represents 5, 10, 15, and 20 h of immersion. A uniform gold

thin film of �250 nm thickness was deposited on a glass sub-

strate using EMITECH SC7620 sputter coater.

Optical absorption spectra of all MDCS, gold nanopar-

ticles solution and sputtered gold thin film on glass substrate

were measured using a double beam UV-Vis/NIR spectro-

photometer (JASCO V-670). Spectra were collected with

2 mm diameter spot size for the light beam and a spectral re-

solution of 0.2 nm. The structural features were investigated

using Zeiss Ultra-55 field emission scanning electron micro-

scope (FESEM). For the Raman-scattering enhancement

from the as realized MDCS and gold thin film, BT was used

as an analyte because of its well-known strong Raman activ-

ity, the non-resonant Raman-scattering and formation of

monolayer on the gold surface with possible covalent bond-

ing. The samples were immersed in BT solution for overnight

and rinsed twice in ethanol and once in water to remove the

excess of unattached BT. The samples were finally dried with

dry N2 gas. The Raman-scattering was collected using high

resolution confocal micro-Raman spectrometer (Horiba Jobi-

nYvon, LabRAM-HR 800) equipped with three excitation

wavelengths at 514.5 nm, 632.8 nm, and 785 nm. The laser

power was significantly attenuated by neutral density filters to

0.7 mW before reaching the sample. A 50� objective lens

with a numerical aperture value of 0.75 focused the excitation

beam to �1 lm2 area of the sample. The scattered light was

collected by the same objective lens and passed through

Raman edge filter (blocking bandwidth of �120 cm�1) before

entering the monochromator chamber with 1800 g/mm grating

and a Peltier-cooled charge coupled device (CCD) detector at

�70 �C. Each Raman spectrum was obtained with a 10 s ex-

posure time for the detector. A macro-sampling accessory was

used with a 40 mm focal length lens and a spherical mirror for

double laser pass for recording the normal Raman-scattering

spectrum (NRS) of pure BT solution with all the three differ-

ent excitation wavelengths. All experiments were carried out

at room temperature.

III. RESULTS AND DISCUSSION

A. MDCS characterization

Figure 1(a) shows optical absorption spectra of the as

synthesized Au NPs with LSPR band at 520 nm. An approxi-

mate size of the Au NPs was calculated using the formula23

R ¼Vf � k2

p

2pc � Dk; (1)

where R is radius of metal nanoparticle, Vf is Fermi velocity

of electrons in bulk metal (for gold, Vf¼ 1.39� 108 cm/s), c

SCHEME 1. The schematic diagram

shows the protocol for the fabrication

steps of a metal-dielectric inverse colloi-

dal structure: (a) self-assembled polysty-

rene colloidal crystal; (b) silica solution

infiltrated polystyrene colloidal crystal

structure; (c) an inverse silica opal (ISO)

structure obtained by annealing and sin-

tering processes; (d) amino group func-

tionalization of the ISO structure with

APTES; (e) immobilization of Au Nps on

the silica network.

084303-2 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

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is the light velocity, kp is the peak position of the absorption

band, and Dk is the full-width at half-maximum of the absorp-

tion band. The estimated size of Au NPs is �10 nm in dia-

meter using kp¼ 520 nm and Dk¼ 48 nm in Eq. (1). The

estimated value is in good agreement with the average size

found from FESEM measurement shown in Fig. 2(a). The

absorption spectra (Figure 1(b)) show two bands: one located

at 600 nm due to the PBG and the other at 520 nm due to the

LSPR of Au NPs. The PBG corresponding to the ISO satisfies

the Bragg diffraction given by the modified Bragg formula:8

k ¼ 2� 0:816� D�ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðn2

ef f � Sin2 hÞq

; (2)

where

n2ef f ¼ 0:74� n2

air þ 0:26� n2silica; (3)

and D refers to the diameter of hollow air spheres and h rep-

resents the angle between the direction of incident light and

the normal to the (111) plane of fcc lattice of crystal. neff is

the effective refractive index of the crystal, where nair¼ 1

and nsilica¼ 1.45.

The position of PBG at 600 nm satisfies Eq. (2) for a

sphere diameter of 325 nm which was originally occupied by

the polystyrene bead before being burnt out. This demon-

strates a shrinkage occurring during the sintering process.

This is not surprising as the latex spheres are mesoporous,

and water vapor released from these pores during the calci-

nation leads to a shrinkage of the beads.20 These results are

also in agreement with the FESEM image as shown in Figure

2(a), where the average size of the air gap is around �325

(65) nm. The reflectance spectrum (Figure 1(c)) of ISO was

measured with white light beam of 1 mm diameter at an

angle of incidence of 10� to the normal of crystal growth

(111) plane. The reflection maximum occurring at 591 nm is

in good agreement with the value calculated from Eq. (2).

The oscillations following the reflection maximum are due

to the Fabry-P�erot interference of light reflected from the

end surfaces of the opal. Appearance of the Fabry-P�erot

oscillations is a good indicator of the homogeneity and the

average refractive index of PhCs.24 Fabry-P�erot oscillations

FIG. 1. UV-Vis/NIR absorption spectra of (a) Au NPs solution (b) ISO

doped with Au NPs for different times, (i) ISO, (ii) MDCS-5 h, (iii) MDCS-

10 h, (iv)MDCS-15 h, (v) MDCS-20 h, and (c) normalized white light reflec-

tion spectrum of ISO for 10� angle of incidence.

FIG. 2. (a) MDCS-20 h shows ISO with 325 nm dimension air voids and the

immobilized Au NPs in the silica matrix and (b) MDCS-20 h in cross-

section view shows the immobilization of Au NPs throughout the network

of ISO.

084303-3 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

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also indicate the occurrence of high DOS in the crystal,25

which will be discussed in Sec. III B.

The immobilized Au-NP in the silica matrix can be seen

clearly in the FESEM images shown in Figure 2. Figure 2(a)

gives the top view while Figure 2(b) shows the cross-

sectional image. It is also evident from Figure 2 that the Au

Nps are immobilized uniformly throughout the network of

the ISO without any observable aggregation. From the optical

and structural properties characterization (Figures 1 and 2), it

can be concluded that the resultant novel MDCS obtained

here present the unique features of LSPR of Au NP and PBG

of ISO.

B. Raman scattering measurement

The existence of a PBG in the MDCS could make these

new optical materials fascinating in the field of photonics.

Due to low group velocity vg for the frequencies near the

edges of the PBG,5 the DOS not only reduced in the band

gap but also get enhanced at the band edges due to long opti-

cal path length and by large light matter interaction. Thus,

the strength of the optical field within the crystal may be

enhanced, which constitutes an advantage if one deals with

optically active constituents.9 To study the effect of PBG

here we have employed for the first time the MDCS for

enhancement of Raman-scattering through the well known

SERS mechanism. The Raman spectrum of BT molecules,

which get attached to the Au NPs of the MDCS, was

recorded using three different excitation wavelengths:

514.5 nm, 632.8 nm, and 785 nm. The wavelengths and the

PBG are so chosen that the excitation wavelengths 514.5 nm

falls on the high frequency side of the band edge and

632.8 nm falls on the lower frequency band edge of the PBG.

The 785 nm is chosen such a way that it is far away from the

band gap and on the lower frequency side of the band gap

(Figure 4(a)). Through this choice of wavelengths we plan to

look at PBG effects: precise field confinement in the dielec-

tric and air media, effect on the DOS at the band edges26 and

their contribution towards the enhancement of Raman-

scattering from the analyte. In Figure 3, the intense peaks

centered at 998, 1022, 1070, and 1572 cm�1 appear in

Raman spectrum obtained with the MDCS and gold thin film

as substrates, and they correspond to BT molecule’s in-plane

ring-breathing mode, the in-plane C-H bending mode, the in-

plane ring-breathing mode coupled with the C-S stretching

mode and the C-C stretching mode, respectively.22,29

Raman-scattering spectra recorded with the different

excitations show that Raman signals are strong for the

632.8 nm and 785 nm excitations with the former leading to

more intense spectra than the later (Figure 3(a)). The

Raman-scattering with the 514.5 nm excitation shows very

weak signal (Figure 3(a)) and deviates from the well-known

x4 Raman scattering cross-section, where x is the incident

frequency.27 However, the Raman spectra of the adsorbed

BT molecule on the sputtered gold thin film for the opted ex-

citation wavelengths show the validity of x4 scattering prob-

ability where intense signals were observed for the 514.5 nm

excitation compared to 632.8 nm. Signals were too weak and

did not show up with 785 nm excitation.

Considering the location of the excitation wavelengths

in the optical absorption spectrum of the MDCS (Figure

4(a)), the Stokes Raman bands will be on their respective

longer wavelength side indicated by the bands in Figure 4(a).

For the excitation wavelength of 632.8 nm, which is falling

on the red band edge, the MDCS will have more DOS due to

its fascinating PBG feature compared to a homogenous

system.9

It is evident from Figure 3(a) that Raman signals are

more intense with 632.8 nm excitation than with 514.5 nm

and 785 nm excitations. According to electromagnetic varia-

tional theorem for the PhCs5 the low frequency bands would

be concentrated in the high dielectric (e) or high refractive

index (n) regions, and the high frequency bands have a larger

fraction of their energy in the low refractive index (n)

regions. In 2D and 3D PhC, these media being the high index

dielectric material and the low index air medium, the bands

above the band gap and below the band gap are labeled as

“air band” and “dielectric band,” respectively. In the current

PhC, the excitation wavelengths 632.8 nm, 785 nm and their

respective Raman scattered modes would be below the band

gap (Figure 4(a)) and hence their energy would be concen-

trated in the dielectric medium.28 The dielectric medium in

our MDCS system is a very thin silica matrix with immobi-

lized Au NPs, which is shown with a red circled portion in

Figure 4(b). The 514.5 nm excitation wavelength and their

FIG. 3. Wavelength scanned Raman-scattering of 5 lM BT molecule col-

lected over (a) MDCS-20 h and (b) RF sputtered Gold film for three different

wavelengths 514.5, 632.8, and 785 nm with a power of 0.7 mW next to the

filter. The spectra were offset along the y-axis.

084303-4 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

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Raman scattered modes fall on the higher frequency side of

the band gap (Figure 4(a)) and therefore have their energy

concentrated in the air medium.28 These air voids in the

inverse opal system are �325 nm in diameter and are shown

with yellow circled portion in Figure 4(b). As a consequence,

the 514.5 nm excitation above the band edge has low proba-

bility to interact with Au NPs and LSPR excitation resulting

in weak Raman-scattering signals. On the other hand the

632.8 nm wavelength of excitation falls below the band

edge. This results in the field localized in the dielectric

whose thickness will be just few nanometers leading to high

probability for excitation and enhancement of LSPR and

Raman-scattering of BT molecule adsorbed to the Au NPs.

Since 785 nm is far from the LSPR of gold nanoparticles, the

consequential enhancement of Raman scattering is less

prominent than with 632.8 nm excitation. Further, since the

Raman signal follows the x4 scattering dependency, the scat-

tering should be weaker for 785 nm compared to 632.8 nm.

Because of these two reasons we observe (Figure 3(a)) low

signal strength for 785 nm compared to the 632.8 nm

excitation.

One more important aspect is that the reduced group ve-

locity at the band edge of PBG leads to large light-matter

interaction and enhancement of DOS at the band gap edges

of the PhC. Thus the experimentally observed (Figure 3(a))

more intense Raman signal with the 632.8 nm excitation

compared to 514.5 nm and 785 nm could be ascribed to two

factors: one is the high DOS at band edges of PBG for the

excitation line and Raman scattered modes10 (shaded region

(ii) in Figure 4(a)) and the second, PBG effect along with

plasmonic effect due to possible field confinement in dielec-

tric medium and excitation of LSPR of Au NPs. The calcula-

tion of enhancement due to individual contribution is quite

complex since one factor depends on the other. Hence, to

explain the large enhancement with 632.8 nm wavelength of

excitation, both the contributions need to be taken into con-

sideration. The existence of high DOS in the crystal is also

evident from the reflection spectra25 collected (Figure 1(c))

for the white light’s incidence angle of 10� with respect to

the (111) plane of fcc lattice of ISO. The enhancement of

Raman scattering signal due to the PBG effect in MDCS is

evident when we compare these signal strengths with the sig-

nals observed from BT molecules dispersed on the sputtered

gold thin film. As the gold thin film does not have any PBG

structure, we observe (Figure 3(b)) that the scattering signals

increase as one goes from 785 nm to 514.5 nm through

632.8 nm. This is consistent with the Raman scattering prob-

ability which is proportional to fourth power of incident

frequency.9

From these observations one can infer that for the

MDCS, the field confinement in the dielectric or air medium

and the high DOS available at photonic band edge could

play an important role in the enhancement of the spontane-

ous Raman-scattering.

C. Effectiveness as a SERS substrate

The enhanced Raman-scattering evident (Figure 3(a))

from the plasmonic and PBG effects of MDCS shows its

effectiveness as a suitable SERS substrate compared to sput-

tered gold thin film with the following enhancement factor

(EF). The substrate SERS enhancement factors (SSERS) are

calculated for the well resolved and intense peaks using the

formula27

EF ¼ ISERS=NSERS

INRS=NNRS¼ ISERS

INRS

g1 � VNRS

g2 � VSERS

¼ ISERS

INRS

g1 � r21 � z1

g2 � r22 � z2

where V refers to the exposed volume contributing to the

Raman signals and is calculated separately for the MDCS,

Au film (surface only) and the solution based on their thick-

ness and the Rayleigh range of the focusing objective. r rep-

resents the spot size radius and z represents the Rayleigh

range for each excitation wavelength. 1 and 2 correspond to

the solution and PhC/Au film, respectively. The Rayleigh

range for 50� objective varies from 1 l to 1.6 l for the exci-

tation wavelengths (shorter to longer). Similarly the Ray-

leigh range for the 40 mm focal length lens varies from 1 mm

to 1.6 mm. g represents the molecular density of BT over the

collected region. The maximum reported surface concentra-

tion of BT molecule on a smooth gold film �6.8� 1014 cm�2

FIG. 4. (A) Optical absorption spectrum of (a) sputtered gold thin film, (b)

Au NPs’ aqueous solution and inverse of the transmittance of (c) inverse

silica opal (with PBG centered at 600 nm) and (d) MDCS-20 h (with LSPR

band centered at 520 nm and PBG centered at 600 nm). Raman scattering

range of 900 cm�1–1800 cm�1 recorded for the BT molecule with 514.5,

632.8, and 785 nm wavelengths of excitation are shown as shaded regions

(i), (ii), and (iii), respectively, on the wavelength scale. The spectra are off-

set along the y-axis for clarity. (B) FESEM image of MDCS-20 h shows red

and yellow circled regions for dielectric and air media, respectively.

084303-5 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

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is considered29 and this value is used for both the Au film as

well as the MDCS. In the case of MDCS, the molecular den-

sity over probed volume is calculated by considering the

26% filling fraction of the dielectric medium. The molecular

density of the pure BT solution is 5.9� 1021 cm�3. The

intensities of SERS and NRS are calculated from the area af-

ter fitting the lines to a Lorentzian line shape. The enhance-

ment factors obtained through these measurements are

shown in Table I.

The calculated EFs for both the MDCS and the gold thin

film relative to the NRS of BT solution for the 514.5 nm and

632.8 nm are tabulated in the Table I. We have also shown

the enhancement observed for MDCS relative to the BT mole-

cules dispersed on the gold film in the last column of Table I.

We observe an enhancement of 82 times for the MDCS with

632.8 nm for the 998 cm�1 mode in comparison to the other

modes, which could be because the 998 cm�1 is closer to the

band edge than the other vibrational modes. One can also see

the large enhancement for 632.8 nm excitation compared to

the 514.5 nm. These large enhancements in the Raman signals

strongly support that this novel MDCS can be an effective

SERS substrate for the micro level detection of adsorbed

analyte.

IV. CONCLUSIONS

A novel MDCS is realized by a simple chemical process

through immobilization of Au NPs on the amino group func-

tionalized matrix of silica. Optical and structural character-

izations show unified features of plasmonic properties of

metal nanoparticles and PBG features of colloidal PhCs. The

observations made in respect to MDCS and gold thin film for

Raman-scattering studies of adsorbed BT molecule illus-

trates the effect of band edge DOS and confinement of

modes in specific media of the periodic dielectric structure.

The precise low and high energy field confinements in the

dielectric and air media could find various applications in op-

tical trapping, laser cooling.28 The increase in the light inten-

sity inside the structure could find interesting nonlinear

effects as well.30,31 The intense field at the PBG edges along

with plasmonic effects from metal nanoparticles can be used

in the single molecule detection and reduction of the thresh-

old value for stimulated Raman-scattering.

ACKNOWLEDGMENTS

This work carried under the frame work of ITPAR

Phase-II and UGC-BRNS. The author S. Guddala would like

to acknowledge the financial support of UGC sponsored Ba-

sic Science Research (BSR) fellowship, India. The authors

are grateful to Dr. P. S. R. Prasad, National Geophysical

Research Institute (NGRI), Hyderabad for useful discussions

on Raman scattering studies.

1E. M. Purcell, Phys. Rev. 69, 681 (1946).2P. R. Berman, Cavity Quantum Electrodynamics: Advances in Atomic,Molecular and Optical Physics, Suppl. 2 (Academic, Boston, 1994).

3P. T. Worthing, R. M. Amos, and W. L. Barnes, Phys. Rev. A 59, 865

(1999).4G. L. J. A. Rikken, Phys. Rev. A 51, 4906 (1995).5J. D. Joannopoulos, S. G. Johnson, J. N. Winn, and R. D. Meade, PhotonicCrystals: Molding the Flow of Light, 2nd ed. (Princeton University Press,

Princeton, 2008).6E. Yablonovitch, Phys. Rev. Lett. 58, 2059 (1987).7S. John, Phys. Rev. Lett. 58, 2486 (1987).8C. Lopez, Adv. Mater. 15, 1679 (2003).9S. V. Gaponenko, Phy. Rev. B 65, 140303 (2002).

10T. Ochiai, K. Sakoda, and T. Sawada, Phy. Rev. B 77, 245101 (2008).11L. P. Avakyants, V. S. Gorelik, L. I. Zlobina, N. N. Mel’nik, P. P. Sverbil’,

A. B. Fadyushin, and A. V. Chervyakov, Inorg. Mater. 42, 635 (2006).12K. Kuroda, T. Sawada, T. Ochiai, T. Kuroda, K. Watanabe, and K.

Sakoda, Thin Solid Films 517, 1727 (2009).13D. A. Mamichev, K. A. Gonchar, V. Yu. Timoshenko, G. K. Mussabek, V.

E. Nikulin, and T. I. Taurbaev, J. Raman Spectrosc. 42, 1392 (2011).14S. V. Gaponenko, A. A. Gaiduk, O. S. Kulakovich, S. A. Maskevich, N. D.

Strekal, O. A. Prokhorov, and V. M. Shelekhina, JETP Lett. 74, 309

(2001).15L. Lu, I. Randjelovic, R. Capek, N. Gaponik, J. Yang, H. Zhang, and A.

Eychmu€ller, Chem. Mater. 17, 5731 (2005).16S. Kubo, Z. Ze Gu, D. A. Tryk, Y. Ohko, O. Sato, and A. Fujishima, Lang-

muir 18, 5043 (2002).17G. C. Schatz and R. P. Van Duyne, “Electromagnetic mechanism of

surface-enhanced spectroscopy,” in Handbook of Vibrational Spectros-copy, edited by J. M. Chalmers and P. R. Griffiths (Wiley, New York,

2002), Vol. 1, p. 759.18J. R. Lombardi and R. L. Birke, J. Phys. Chem. C 112, 5605 (2008).19A. Chiappini, C. Armellini, A. Chiasera, M. Ferrari, L. Fortes, M. Clara

Gonc-alves, R. Guider, Y. Jestin, R. Retoux, G. Nunzi conti, S. Pelli, R.

M. Almeida, and G. C. Righini, J. Non-Cryst. Solids 355, 1167 (2009).

TABLE I. Approximated SERS substrate enhancement factor and relative enhancement for MDCS.

Raman shifta (cm�1)

Enhancement factorb (�106)

MDCSc Au thin filmc Enhancementd MDCS/Au film

514.5 nm 632.8 nm 514.5 nm 632.8 nm 514.5 nm(�10�2) 632.8 nm

998 0.01 0.82 0.70 0.01 1.43 82.0

1022 0.05 2.42 0.11 0.11 45.45 22.0

1070 0.11 10.11 0.66 0.41 16.66 24.65

1572 0.18 10.39 0.54 0.70 33.33 14.84

aOnly the intense vibration modes of BT molecule are considered for EF calculation.bAll the EF values for MDCS and Au thin film are with respect to the NRS of BT.cEFs for MDCS and Au thin film are approximated with respect to pure BT molecule Raman spectra for each, 514.5 nm and 632.8 nm, wavelengths of

excitation.dEnhancement is calculated by taking the ratio of EFs for MDCS and Au thin film for the concerned excitation line.

084303-6 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

Downloaded 27 Nov 2012 to 14.139.69.1. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions

20A. Chiappini, C. Armellini, A. Chiasera, Y. Jestin, M. Felrari, M. Mattar-

elli, M. Montagna, E. Moser, C. Tosello, L., Zampedri, G. Nunzi Conti, S.

Pelli, R. M. Almeida, and G. C. Righini, Optoelectron. Lett. 3, 184 (2007).21J. Turkevich, P. C. Stevenson, and J. Hillier, Discuss. Faraday Soc. 11, 55

(1951).22S. Guddala, A. Chiappini, G. Alombert-Goget, C. Armellini, M. Ferrari,

K. Shadak Alee, D. Narayana Rao, A. Chiasera, E. Moser, S. Berneschi,

G. Nunzi Conti, G. C. Righini, and P. F�eron, Proc. SPIE 8173, 817317

(2011).23J. Shin, K. Jang, K.S. Lim, I. B. Sohn, Y. C. Noh, and J. Lee, Appl. Phys.

A 93, 923 (2008).24T. Maka, D. N. Chigrin, S. G. Romanov, and C. M. Sotomayor Torres,

Prog. Electromagn. Res. 41, 307 (2003).

25J. M. Bendickson, J. P. Dowling, and M. Scalora, Phy. Rev. E 53, 4107

(1996).26I. S. Nikolaev, W. L. Vos, and A. F. Koenderink, J. Opt. Soc. Am. B 26,

987 (2009).27E. Le Ru and P. Etchegoin, Principles of Surface-Enhanced Raman Spec-

troscopy: and Related Plasmonic Effects, 1st ed. (Elsevier, 2009).28O. Toader, S. John, and K. Busch, Opt. Express 8, 217 (2001).29A. D. McFarland, M. A. Young, J. A. Dieringer, and R. P. Van Duyne, J.

Phys. Chem. B 109, 11279 (2005).30X. Zhu, J. Wang, P. Lau, D. Nguyen, and R. A. Norwood, Appl. Phys.

Lett. 97, 093503 (2010).31P. P. Markowicz, H. Tiryaki, H. Pudavar, and P. N. Prasad, N. N. Lepesh-

kin, and R. W. Boyd, Phy. Rev. Lett. 92(8), 083903 (2004).

084303-7 Guddala et al. J. Appl. Phys. 112, 084303 (2012)

Downloaded 27 Nov 2012 to 14.139.69.1. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions