silver nanoclusters decked diamond thin film as a substrate for surface enhanced raman scattering

Silver nanoclusters decked diamond thin film as a substrate for surface-enhanced Raman scattering , , , , Harish Ojha , Upender Gangadharani , Satyavathi Ravulapalli , Mohan Kumar Kuntumalla , Vadali Venkata , Satya Siva Srikanth , Narayana Rao Desai, and Chandrahas Bansal Citation: AIP Advances 2, 032102 (2012); doi: 10.1063/1.4738367 View online: http://dx.doi.org/10.1063/1.4738367 View Table of Contents: http://aip.scitation.org/toc/adv/2/3 Published by the American Institute of Physics AIP ADVANCES 2, 032102 (2012) Silver nanoclusters decked diamond thin film as a substrate for surface-enhanced Raman scattering Harish Ojha,1,a Upender Gangadharani,2,a Satyavathi Ravulapalli,2,a Mohan Kumar Kuntumalla,1,a Vadali Venkata Satya Siva Srikanth,1,b Narayana Rao Desai,2 and Chandrahas Bansal2 School of Engineering Sciences and Technology (SEST), University of Hyderabad, Hyderabad 500046, India School of Physics, University of Hyderabad, Hyderabad 500046, India (Received 19 February 2012; accepted July 2012; published online 13 July 2012) Modified diamond thin film surfaces are proven candidates for bio-sensoric applications A typical polycrystalline diamond thin film surface decked with silver (Ag) nanoclusters is found to be suitable for surface-enhanced Raman scattering (SERS) Simple and time effective procedures are used to fabricate Ag nanoclusters/diamond/silicon structure Standard Rhodamine 6G probe molecules are used to access the SERS activity of the test surface The observed SERS activity is explained in terms of predominant electromagnetic enhancement mechanism This work is expected to benefit SERS based bio-sensing with diamond as the core sensing material Copyright 2012 Author(s) This article is distributed under a Creative Commons Attribution 3.0 Unported License [http://dx.doi.org/10.1063/1.4738367] Since the advent of surface-enhanced Raman scattering (SERS) there has been a continuous effort to develop stable and reproducible SERS active substrates that not only provide a large enhancement factor but are also useful in analytical applications like bio-sensing.1 However, most of the substrates lack long-term stability due to instability of metal nanostructures deposited on the substrate surface and/or the substrate itself.1 On the other hand, owing to its diverse intrinsic properties, diamond thin film has established itself as an exceptionally stable electro-chemical transducer.2 Diamond thin film’s dielectric properties3 are anticipated to help in the enhancement of surface plasmons resonance4 and thereby enabling itself to detect bio-molecular interactions in real time based on SERS.4 Moreover, over the past decade, diamond thin film has been developed as an attractive bio-sensoric material.5 In this work, a typical polycrystalline diamond thin film surface decked with silver (Ag) nanoclusters is shown as a suitable substrate for SERS Standard Rhodamine 6G (R6G) probe molecules are used to access the SERS activity of the test surface.6 This work is expected to benefit SERS based bio-sensing using selective SERS metal (like Ag)/diamond/silicon (Si)/back contact (like Aluminum) structured metal-insulator-semiconductor devices Polycrystalline diamond thin film considered in this study was deposited on p-type (100) Si substrate using microwave plasma enhanced chemical vapor deposition technique Submicron sized diamond grains constituted the microstructure of the thin film The detailed deposition procedure and other characteristics of this diamond thin film have been previously reported.7, The polycrystalline diamond thin film used in this work is a typical one and has been proven to have bio-sensoric activity.9, 10 Ag nanoclusters are deposited on the diamond thin film surface using a magnetron cluster deposition system (NANODEP 60 from Oxford Applied Research, UK) following a previously reported procedure.11 Ag nanoclusters deposition was carried out for only in order to avoid formation of any thick coating of Ag which may be unfavorable for SERS activity Field emission scanning electron microscope (Carl Zeiss, Ultra 55 system) operated at an accelerating voltage of a Equally contributed to this work b Electronic mail: vvsssse@uohyd.ernet.in 2158-3226/2012/2(3)/032102/5 2, 032102-1 C Author(s) 2012 032102-2 Ojha et al AIP Advances 2, 032102 (2012) FIG (a) Low magnification plane view secondary electron micrographs of Ag nanoclusters decked diamond thin film; (b) the corresponding high magnification micrograph As-deposited diamond thin film surface is shown in the inset kV was used to study the surface morphology of the as-deposited and Ag nanoclusters decked diamond thin film Energy dispersive x-ray (EDX) analysis was carried out at an accelerating voltage of 16 kV 10 μl of 5×10−5 M R6G aqueous solution was dropped onto the test surface The wet test surface (with R6G) are kept undisturbed and allowed to dry naturally Room temperature SERS activity of R6G adsorbed on the test surface was recorded using 514.5 nm laser line equipped micro Raman spectrometer (Horiba Jobin Yvon LABRAM-HR-800) The typical laser power was kept at 2.6 mW in order to avoid any thermal influences The laser beam (spot diameter ∼ μm) was focused onto the test surface (with and without R6G) with a 50x objective lens with numerical aperture of 0.7 SERS signals are collected in the spectral range of 50 to 2000 cm−1 with a spectral resolution of cm−1 in a back scattering geometry perpendicular to face of the (100) Si substrate with only sec integration time Raman spectrometer was calibrated using the standard 521 cm−1 band of Si Ag nanoclusters (deposited using the same experimental conditions as in the case of diamond thin film) decked microscope glass slide and single crystalline silicon p-type (100) are also considered as test surfaces in this study for comparison purposes The secondary electron micrographs of Ag nanoclusters decked diamond thin film surface are shown in Fig Fig 1(a) shows the original morphology impression of the underlying diamond thin film It is also evident from the micrographs that the Ag nanoclusters are uniformly decked throughout the diamond thin film surface EDX analysis confirmed the presence of Ag on the surface SERS data obtained from R6G molecules adsorbed on as-deposited and Ag nanoclusters decked diamond thin film surfaces are shown in Fig For convenience Raman spectra obtained from asdeposited (Fig 2(c)) and Ag nanoclusters decked (Fig 2(b)) diamond thin film surfaces are also included in Fig Raman bands at 1135, 1332, 1483, and 1550 cm−1 in Fig 2(c) are often seen in the Raman spectrum of a typical diamond thin film The broad 1332 cm−1 Raman peak indicates the presence of small diamond crystallites in the diamond film.12, 13 The appearance of Raman band at 1135 cm−1 (with an accompanied band at 1480 cm−1 ) is due to the presence of trans-polyacetylene segments in the grain boundary regions of the diamond thin film.14 Another broad Raman band at 1550 cm−1 called the ‘G’ band, is attributed to sp2 bonded graphite present in the grain boundaries between the diamond crystallites in the film.14–16 Before discussing further about SERS signals from R6G molecules, it is important to note (Fig 2) that Ag nanoclusters decked diamond thin film did not result in any SERS signal from the underlying diamond phase Therefore, SERS data obtained from R6G molecules adsorbed Ag nanoclusters deposited diamond thin film surface have no interference from Raman signals corresponding to the underlying diamond phase SERS signals corresponding to R6G molecules immobilized on as-deposited diamond thin film surface are not observed (Fig 2(a)); the reasons for this is the absence of any interaction between R6G molecules and the test surface at the atomic level and too low concentration of R6G molecules on the test surface to scatter Raman signals On the other hand, SERS signals corresponding to R6G molecules adsorbed on Ag nanoclusters decked diamond thin film are highly amplified and can be observed (Fig 2(d)) at ∼612, ∼772, ∼920, ∼1130, ∼1188, ∼1312, ∼1362, ∼1506, ∼1572, and ∼1649 cm−1 11 The reason for this is the creation of an apt condition for SERS It is evident that the presence of Ag nanoclusters has resulted in SERS signals from R6G molecules This is attributed to the surface plasmon resonance of the Ag nanoclusters Ag has been commonly used to study trace amounts of Raman active materials using SERS methodology.1 032102-3 Ojha et al AIP Advances 2, 032102 (2012) FIG Raman spectra obtained from (a) R6G on diamond thin film (b) Ag deposited diamond thin film (c) as-deposited diamond thin film, and (d) R6G adsorbed on Ag deposited diamond thin film Raman scattering resonance region depends upon the plasmon energy of the metal particles used to create an apt condition for SERS For Ag particles, the resonance region is in the range 1300–1500 cm−1 The presence of two very high intensity SERS signals corresponding to R6G molecules at 1312 and 1362 cm−1 , which fall in the resonance region of Ag confirms that R6G molecules are adsorbed on the test surface Additionally, the enhancement of R6G vibrational modes at ∼612 and ∼1649 cm−1 suggests that the enhancement originates due to the charge transfer from the Fermi level of the Ag metal to the lowest unoccupied molecular orbital of the adsorbed molecules, which changes the effective polarizability of the molecules, in-turn resulting in the observed SERS activity.11 In the present context, this electromagnetic effect can originate from the localized surface plasmon resonance of the Ag nanocluster aggregates17 on the diamond films These aggregates can generate a huge electromagnetic field at the junction sites If there is Raman signal enhancement mainly through any chemical mechanism,1 R6G molecules immobilized on the as-deposited diamond thin film could have been detected using Raman scattering Fig shows high quality Raman spectra (only for comparison purposes) obtained from R6G molecules adsorbed on Ag nanoclusters decked on diamond film, p-type (100) Si surface and on as-deposited diamond film It is evident that Si also shows SERS activity However, it should be noted that Si cannot replace diamond/Si structure for any further bio-sensing device fabrication The comparison of the spectra reveals the existence of different SERS enhancements A simple quantitative intensity comparison is shown in Fig for a selected Raman band at ∼1650 cm−1 It can be clearly observed that the Raman signal enhancement in the case of Ag nanoclusters decked diamond film is better than that in Si Furthermore, reproducibility (refers to the ability to produce SERS signal at various locations of the SERS active surface with as minimum as possible intensity variation) of the SERS activity of Ag nanoclusters decked diamond thin film has been checked SERS spectra obtained from R6G molecules adsorbed at several positions on Ag nanoclusters decked diamond film are shown in Fig The intensities of Raman bands at ∼613, ∼773, ∼1186, ∼1362, ∼1509, ∼1533, ∼1576, and ∼1649 cm−1 are quantified using Loretzian fit The results showed that the intensity variations of all the Raman bands are less than 5%, which is an acceptable value This in turn shows that the test surface is homogeneous Here, it is also very important to mention that the fabricated Ag nanoclusters decked diamond thin film showed the same reproducibility even after leaving it in ambient conditions for days together This shows that neither Ag nanoclusters degraded nor the underlying diamond In another simple experiment, to check the reusability of the SERS substrate under consideration, the substrate was ultrasonicated in methanol to remove the adsorbed R6G molecules Then, freshly prepared R6G solution was dropped and allowed to dry naturally following the procedures described in the beginning Raman signals with the similar intensity from R6G could be again detected It was found that the fabricated SERS substrate is reusable for at least two times Thereafter, the Raman signal intensity would reduce 032102-4 Ojha et al AIP Advances 2, 032102 (2012) FIG Raman spectra obtained from R6G molecules on (a) Ag nanoclusters decked diamond thin film, (b) Ag nanoclusters decked Si, and (c) as-deposited thin diamond film FIG Reproducible SERS spectra obtained from R6G molecules at different locations on Ag nanoclusters decked thin diamond film In conclusion, a stable Ag nanoclusters decked diamond film demonstrates an excellent and reproducible SERS activity which is explained in terms of the well-known electromagnetic enhancement mechanism The diamond film used in the present experiments is a typical one and can be deposited on a variety of substrates with ease Similarly, Ag nanoclusters deposition procedure used in this work is not only very easy but also not time consuming Even though the R6G molecules’ concentration used in the present study is good enough for practical applications, the detection limits have to be further determined The influence of Ag nanoclusters size, morphology, distribution etc., on any further enhancement and detection limits is the subject of future investigation The authors wish to thank Ms Deepthi and Mr Lakshmi Narayana (Technical staff at School of Physics, University of Hyderabad) for helping us with Raman measurements and scanning electron microscopy, respectively The authors R Sathyavathi and G Upender acknowledge DST and UGC for providing financial support through Women Scientist Scheme (SR/WOS-A/PS-06/2009) and Dr D S Kothari post-doctoral fellowship programme, respectively The diamond thin film was deposited by VVSSS during his employment at Institute of Materials Engineering, University of Siegen, Germany K C Bantz, A F Meyer, N J Wittenberg, H S Im, O Kurtulus¸, S H Lee, N C Lindquist, S H Oh, and C L Haynes, Phys Chem Chem Phys 13, 11551 (2011) C E Nebel, B Rezek, D Shin, H Uetsuka, and N Yang, J Phys D: Appl Phys 40, 6443 (2007) O Auciello and A V Sumant, Diam Relat Mater 19(7–9), 699 (2010) A M Michaels, J Jiang, and L Brus, J Phys Chem B 104, 11965 (2000) 032102-5 W Ojha et al AIP Advances 2, 032102 (2012) S Yang, O Auciello, J E Butler, W Cai, J A Carlisle, J Gerbi, D M Gruen, T Knicker-bocker, T L Lasseter, J N Russell, L M Smith, and R J Hamers, Nature Materials 1(4), 253 (2002) P Hildebrandt and M J Stockburger, J Phys Chem 88, 5935 (1984) V V S S Srikanth, T Staedler, and X Jiang, Appl Phys A 91, 149 (2008) V V S S Srikanth, PhD thesis, University of Siegen, Siegen, Germany, 2008 H Zhuang, V V S S Srikanth, X Jiang, J Luo, H Ihmels, I Aronov, B W Wenclawiak, M Adlung, and C Wickleder, Appl Phys Lett 95, 143703 (2009) 10 H Zhuang, V V S S Srikanth, X Jiang, I Aronov, B W Wenclawiak, J Luo, and H Ihmels, Chemistry of Materials 22, 4414 (2010) 11 G Upender, R Satyavathi, B Raju, K Shadak Alee, D Narayana Rao, and C Bansal, Chem Phys Lett 511, 309 (2011) 12 W A Yarbrough and R Messier, Science 247, 688 (1990) 13 J Lee, R W Collins, R Messier, and Y E Strausser, Appl Phys Lett 70, 1527 (1997) 14 A C Ferrari and J Robertson, Phys Rev B 63, 121405 (2001) 15 L Fayette, B Marcus, M Mermoux, L Abello, and G Lucazeau, Diam Relat Mater 3, 438 (1994) 16 S Prawer and R J Nemanich, Phil Trans R Soc Lond A 362, 2537 (2004) 17 S.-P Chen, C M Hosten, A Vivoni, R L Birke, and J R Lombardi, Langmuir 18, 9888 (2002)