%0 Journal Article
%T Gold Nanoparticles as Probes for Nano-Raman Spectroscopy: Preliminary Experimental Results and Modeling
%A V. Le Nader
%A J.-Y. Mevellec
%A T. Minea
%A G. Louarn
%J International Journal of Optics
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/591083
%X This paper presents an effective Tip-Enhanced Raman Spectrometer (TERS) in backscattering reflection configuration. It combines a tip-probe nanopositioning system with Raman spectroscope. Specific tips were processed by anchoring gold nanoparticles on the apex of tapered optical fibers, prepared by an improved chemical etching method. Hence, it is possible to expose a very small area of the sample (~20£¿nm2) to the very strong local electromagnetic field generated by the lightning rod effect. This experimental configuration was modelled and optimised using the finite element method, which takes into account electromagnetic effects as well as the plasmon resonance. Finally, TERS measurements on single-wall carbon nanotubes were successfully performed. These results confirm the high Raman scattering enhancement predicted by the modelling, induced by our new nano-Raman device. 1. Introduction The Raman effect is a well-known phenomenon of the inelastic diffusion of light, with change in the frequency of the incident radiation passing through materials or molecules. In the spectrum of the scattered light, new bands can be observed, and their energies are characteristic of the chemical nature of the investigated object. Raman spectroscopy is a useful tool, which is widely used in academic and industrial laboratories. This nondestructive spectroscopy provides structural information about various materials and can be exploited to build sensors that operate in different areas such as gas detection or bio- and chemical sensing. Generally, these equipments were built from an optical system that analyzes the diffusion of the light and transfers this information to spectroscopic detectors and finally to the electronic system for data processing. Nevertheless, the weakness of the signal does not allow the investigation of single molecules or individual nanoobjects. However, in the 70s, it was observed and proved [1¨C3] that Raman intensity can be strongly enhanced using a specific surface-sensitive technique based on the optical properties of noble metals, such as silver or gold. Nowadays, this phenomenon is well known and commonly called Surface Enhanced Raman Scattering (SERS) effect. This enhancement occurs for molecules adsorbed on rough metal surfaces or on metal nanoparticles. The main Raman enhancement contribution is attributed to the excitation of surface plasmons-polaritons resonances (collective oscillations of the electrons localised near the surface of metals) occurring near metallic nanostructures. The interaction of light with metallic nanoparticles is
%U http://www.hindawi.com/journals/ijo/2012/591083/