Highly Efficient SERS Nanowire/Ag Composites

Abstract

Abstract : Optically based sensing provides advantages over electronic sensing because optical spectra can uniquely finger print a chemical compound, significantly reducing false alarms and simplifying the detection process. In addition, light can easily be directed over long distances, enabling remote sensing. In Raman scattering (RS), light is scattered from a chemical of interest and the vibrational modes in the chemical red shift the frequency of the scattered light, producing a spectrum of lines that are characteristic of that molecule. A major issue for ordinary Raman scattering is that its cross-sections are very small, resulting in low sensitivity (1E-8 of the intensity of the exciting laser). For most solids and liquids, this is not a problem because of the large numbers of molecules or atoms that are exposed to the laser light. In the case of trace amounts of molecules in gases or liquids, detection through ordinary Raman scattering is virtually impossible. However, the Raman signal can be enhanced by many orders of magnitude by the use of metal nano particles1, which is referred to as surface enhanced Raman scattering (SERS). The SERS enhancement of molecules adsorbed on the roughened metal surface is caused by local electromagnetic fields that are created by the laser excitation of surface plasmons at the metal surface. In addition, it has been shown that local hot spots in the electric fields produced by interactions of localized plasmons on adjacent or neighboring nanoparticles can produce even larger SERS effects2. Unfortunately, although the SERS effect has been recognized for a long time, a full understanding of the phenomenon has not yet been achieved. This lack of understanding limits its application potential, in that it is difficult to produce highly sensitive, inexpensive and highly repeatable SERS substrates.