SERS study of molecules on Ag nanocluster films deposited on glass and silicon substrates by cluster deposition method G. Upender, R. Sathyavathi, B. Raju, C. Bansal, D. Narayana Rao ⇑ School of Physics, University of Hyderabad, Hyderabad 500 046, India article info Article history: Received 26 September 2011 Received in revised form 10 December 2011 Accepted 24 December 2011 Available online 5 January 2012 Keywords: SERS Crystal Violet Ag nanoclusters Glass p-type Si(1 0 0) abstract Ag nanoclusters were deposited on glass as well as p-type Si(1 0 0) wafers using a nanocluster deposition system and subsequently annealed at 300 °C for 2 h to achieve desirable cluster sizes which tune the sur- face plasmon resonance (SPR) for SERS studies. The surface morphology of these substrates was examined through FESEM images. The SERS studies were carried out on these substrates with 100 lM and 1 lM Crystal Violet (CV) as a test molecule using 514.5 and 632.8 nm as excitation wavelengths. The depen- dence of SERS enhancement on the nature of the substrate, shape, size and inter particle distance of Ag nanoclusters is briefly discussed. The experimental findings suggest that the SERS enhancement is higher on glass substrate compared to p-type Si(1 0 0) substrate. The substrates investigated in this study were highly reproducible, repeatable and stable. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Soon after the discovery of Surface Enhanced Raman Scattering (SERS) as a tool for the detection of organic/bio molecules at the ul- tra low level concentration, it has been growing as one of the promising areas of research in nanoscience and technology due to its power as an analytical tool for sensitive and selective detec- tion of molecules adsorbed on noble metal (Au, Ag, Cu etc.,) nano- structures [1–3]. The commonly used SERS-active substrates have been prepared by employing many chemical and physical routes. The chemical route is based on aggregated Ag and Au colloids and these metal colloid solutions of Ag or Au particles of nanome- ter size have shown high SERS enhancement factors [4–8]. The problem involved in this method is that the tendency for colloidal particles to aggregate spontaneously upon addition of analytes leads to poor stability of system and irreproducibility in the mag- nitude of SERS signals [9,10]. The substrates made of electrochem- ically roughened gold and silver surfaces, are relatively easy to produce and present good SERS enhancement, however, their reproducibility is poor [11]. But these problems were slightly over- come in the physical route. SERS effects of various nanostructures, for example, flowerlike Ag nanostructures [12], Ag nanowire bun- dles [13], Ag nanorod arrays [14], Ag nanoparticles [15], Ag nanowell and nanopore array [16,17] and bimetallic (Ag–Au) substrates [18] were reported in the literature. Among them, lithographic technique provides highly organized nanostructures that lead to high sensitivity and reproducibility [19,20]. However, this technique is quite expensive and requires elaborative prepara- tion methods. Both the chemical and physical routes have their advantages and drawbacks and hence both of them are currently used for the preparation of highly efficient SERS substrates. In this context, there is a need to develop cheaper and reliable substrates for enhancing the sensitivity and reproducibility of the SERS signals. The present work is carried out to fabricate a suitable SERS sub- strate using a physical route namely cluster deposition method with Ag as target. This method offers ease of fabrication and also provides nanoparticles with high purity. It also allows fabricating variety of nanoparticles using various target metals like Au, Cu, and Pd etc. From the literature it is well established that the SERS intensity depends on the excitation of the localized surface plas- mon resonance (LSPR), which in turn depends upon many factors such as shape, size and inter particle spacing of the material. Based on these points we optimized the Ag nanoclusters (from hereafter it is referred to as Ag NC’s) size and density through a cluster depo- sition system [21]. Our recent report [21] shows that this prepara- tion method can generate SERS substrates suitable to detect ultra low concentrations of molecules. Following the research line of this work, we were motivated to take up the present work to study the suitability of an efficient substrate for SERS. Very few studies have been published on the influence of the nature of the substrates of nanoparticles in SERS measurements [22,23]. Thus it seems dependency of the nature of the substrates has been ignored or given less priority in the field of SERS. There- 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.12.044 ⇑ Corresponding author. Tel.: +91 40 23134320; fax: +91 40 23010227. E-mail addresses: cbsp@uohyd.ernet.in (C. Bansal), dnrsp@uohyd.ernet.in (D. Narayana Rao). Journal of Molecular Structure 1012 (2012) 56–61 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc