Surface Raman chemical enhancement

Although chemisorption is not essential, when it does occur there may be further enhancement of the Raman signal, since the formation of new chemical bonds and the consequent perturbation of adsorbate electronic energy levels can lead to a surface-induced RR effect. The combination of surface and resonance enhancement (SERRS) can occur when adsorbates have intense electronic absorption bands in the same spectral region as the metal surface plasmon resonance, yielding an overall enhancement as large as 10lo-1012. 

Figure 10.1. Comparison of normal (top) and surface-enhanced (bottom) Raman scattering. The top panel shows the conversion of incident laser light of intensity /(vl) into Stokes scattered light /NRS, which is proportional to the Raman cross section and the number of target molecules N in the probed volume. In the bottom panel

Fromm DP, Sundaramurthy A, Kinkhabwala A, Schuck PJ, Kino GS, Moemer WE (2006) Exploring the chemical enhancement for surface-enhanced Raman scattering with Au bowtie nanoantermas. J Chem Phys 124(6) 061101... 

Chemical enhancement (CE) The interaction of molecules with metallic surfaces may be behind an additional increase in the Raman scattering and this is called chemical enhancement (CE). 

Chemical Enhancement Compared to electromagnetic enhancement, aspects of the contribution of chemical enhancement [27-29], are less known. Chemical enhancement has other synonyms such as charge transfer (CT) and the short-range effect. It is associated with the electronic structure (state) of the metal and the adsorbate, which can be explained by a resonance-like Raman mechanism (vide infra). As most of the electrochemical SERS systems involve the formation of strong or weak chemical bonds for the adsorbate with the electrode surface, it is... 

The molecular orbital molecule-surface interaction generates new electronic states that can be resonant with light laser at lower frequencies than the states of either the molecule or the surface. This is the so called chemical enhancement, the other SERS important mechanism (12). The results presented here demonstrate that the signals of the Raman spectrum of the target nitroaromatic HE TNT and DNT are enhanced strongly by contact with the metal oxide particles. Since Raman signal enhancement is clear in this experiment, other mechanisms could be responsible for the enhancement factors found. 

---