Vibrational Spectroscopy 68 (2013) 153–157 Contents lists available at ScienceDirect Vibrational Spectroscopy journa l h om epage: www.elsevier.com/locate/vibspec Short communication Surface-enhanced Raman scattering measurements on silver nanoparticles covered with differently formed platinum films Sebastian Wojtysiak, Andrzej Kudelski ∗ Faculty of Chemistry, University of Warsaw, Pasteur 1, PL-02-093 Warsaw, Poland a r t i c l e i n f o Article history: Received 15 April 2013 Received in revised form 4 July 2013 Accepted 11 July 2013 Available online 22 July 2013 Keywords: SERS Platinum Silver Core–shell nanoparticles a b s t r a c t Gold and silver electromagnetic nanoresonators covered by a thin layer of platinum are often used to study adsorption of various molecules on “model platinum surfaces” with surface-enhanced Raman scattering (SERS) spectroscopy. In this contribution spectra of pyridine adsorbed on films formed from core–shell Ag@Pt and Ag@Ag–Pt nanoparticles and pure Pt or Ag nanoparticles were measured using a confocal Raman microscope. The SERS spectra of pyridine adsorbed on alloy Ag@Ag–Pt nanoparticles could not be obtained as a linear combination of spectra measured on pure Ag and Pt surfaces. In other words, for silver electromagnetic nanoresonators covered by platinum there is no simple correlation between the “quality” of the deposited Pt layer and the relative intensity of SERS bands characteristic for adsorbate interacting with silver. The SERS spectra accumulated from various places of a film formed from Ag@Pt or Ag@Ag–Pt nanoclusters may differ significantly. Using Ag@Pt nanoparticles with practically negligible amount of Ag on the surface (as per the stripping measurement), it is possible to record SERS spectrum in which the contribution characteristic for pyridine adsorbed on the Ag surface is well visible. It means that, even for macroscopic samples of core–shell Ag–Pt nanoparticles, averaging of many spectra measured at various locations of the sample should be carried out to characterize reliably their properties. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In various fields of materials science it is of great importance to identify the adsorbed species, to determine their orientation with respect to the surface and to observe how the strength of various chemical bonds change upon adsorption. Information of this sort can be obtained, for example, by surface-enhanced Raman scatter- ing (SERS) [1]. To measure the SERS spectrum one has to create a system of electromagnetic nanoresonators, and then to deposit molecules to be analyzed on such nanoresonators (or put in their close proximity). Due to the local enhancement of the electromag- netic field, the intensity of measured Raman spectrum of those “analyzed molecules” increases significantly (for Raman bands with small Raman shifts the increase is roughly proportional to the forth power of the field enhancement) [1–3]. Although the increase of the Raman intensity due to the SERS effect is mainly a result of the enhancement of the electric field, a part of the SERS enhance- ment is also due to the so-called charge transfer enhancement that resembles the ordinary resonance Raman process occurring in metal-ligand complexes [4,5]. ∗ Corresponding author. Tel.: +48 228220211. E-mail address: akudel@chem.uw.edu.pl (A. Kudelski). The most important limitation for wider applications of SERS in surface science is restriction of the materials from which highly efficient (giving enhancement of the efficiency of Raman scatter- ing above 10 4 ) nanoresonators may be formed to the IB metal (Ag, Au and Cu) [1,4]. Construction of nanoresonator from other metals (including commercially very important platinum-group metals) is also possible, but the achieved Raman enhancement factors are not higher than 3 orders of magnitude [5–7]. The first strategy allow- ing to study surfaces of various metals with SERS was developed by Fleischmann et al. and involved coating the highly SERS-active Ag or Au electrodes by thin films of other metals [8,9]. This technique was further improved for the Pt-group metals by Weaver et al., who proposed using ultrathin (2–5 monolayer) pinhole-free elec- trodeposits of such metals on mildly roughened (SERS-active) gold surfaces [10,11]. Although Tian et al. later showed that it is also pos- sible to obtain reliable SERS spectra on the Pt-group metals by the proper nanostructuring of their surfaces [12,13], some groups still use the strategy of deposition of a thin film of a Pt-group metal on the surface of Au or Ag nanoresonators to study SERS on surfaces of Pt-group metals [14,15]. Therefore, Au@Pt and Ag@Pt clusters are of practical significance in SERS spectroscopy. In this contribution we compare SERS spectra of pyridine adsorbed on pure Ag and Pt nanoparticles with the SERS spectra of pyridine adsorbed on Ag@Pt and Ag@Ag–Pt nanoparticles (the rationale of using Ag instead of Au surfaces is that SERS spectra of pyridine adsorbed on Ag and 0924-2031/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vibspec.2013.07.003