Enhanced Raman Effect

Jackson J.B., Westcott S.L., Hirsch L.R., West J.L., Halas N.J., Controlling the surface enhanced Raman effect via the nanoshell geometry, Appl. Phys. Lett. 2003 82 257-259. 

SERS and SERRS, in particular, are well positioned for applications in the area of highly sensitive and specific biological and chemical detection. This is due primarily to emerging advances in nanotechnology and the development of miniature laser sources and light detection techniques. Two recent reports clearly point to the feasibility of developing sensors based on the surface-enhanced Raman effect. 

To unravel a possible resonance-enhanced Raman effect in oxides with partially reduced cations, single phase, well-crystallized binary, ternary, and quaternary mixed oxides were synthesized by chemical vapor... 

The molecular cross section of the ordinary Raman effect can be considerably enhanced. If the exciting radiation has a higher frequency, the intensity increases basically by the fourth power of the frequency. Moreover, there is a further increase as electronic absorption bands are approached the pre-resonance and resonance Raman effect (Sections 3.6 and 6.1). Further, the so-called surface-enhanced Raman effect (SERS) increases the molecular cross section. Both effects produce an enhancement of several orders of magnitude (Gerrard, 1991) (see Sec. 6.1). However, these two effects have to be carefully adapted to the specific properties of the investigated molecules. Photochemical decomposition and excitation of fluorescence may make it impossible to record a Raman spectrum. The described techniques may thus be of considerable importance for the solution of special problems, but they are by no means routine techniques to be generally used. 

Vidugiris, G.J.A., Gudavicius, A.V., Razumas, V.J., and Kulys, J.J. (1989) Structure-potential dependence of adsorbed enzymes and amino adds revealed by the surface enhanced Raman effect European Biophysis Journal, 17, 19-23. 

J. Billmann, G. Kovacs and A. Otto, Enhanced Raman effect from cyanide adsorbed on a silver electrode. Surf. Sci. 92,153 (1980). 

Fig. 10.15 Raman spectrum demonstrating gold-coated AFM tip that causes a local surface-enhanced Raman effect on a sulfur film (A). When the beam is focused away...

Silver is an example of a metal that shows the surface-enhanced Raman effect. After a special surface treatment, the signal of a molecular group on the surface of the metal is enhanced by several orders of magnitude. One successful surface treatment is deposition of silver. So, after starting silver deposition from a cyanide electrolyte on a platinum electrode, a Raman signal of the CN-stretch vibration develops and reaches a limiting value (Figure 7.28). ... 

The Raman signal can be increased by increasing the Raman scattering cross section, a, and electromagnetic enhancement factor, T [13]. The a value can be increased by introducing the RR effect or surface enhancement Raman effect (the chemical effect), as already discussed. L... 

Despite the extensive studies of the anodic layers on Pt with various ultraviolet-visible optical methods, they have not provided a clear indication of the electronic or structural properties of the layers. Rather these optical methods have been more than just another form of readout to complement the electrochemical measurements of charge and current response of the layer to potential and time. Vibrational spectroscopic data from infrared and Raman measurements would be more helpful in establishing the nature of the layers but it is difficult to use these techniques to study metal-electrolyte and similar interfaces because of solvent interference and sensitivity problems. A noteworthy exception is the quite successful in situ use of Raman spectroscopy to study the electrochemically formed oxide layers on silver by Kotz and Yeager. In the instance of silver electrodes, there is a large surface enhanced Raman effect and the signal-to-noise ratio is not a problem. Unfortunately this is not the situation with other metal surfaces such as Pt. Even so, with improved instrumentation there is hope that in situ Raman studies of the anodic layers on Pt will become practical. 

Controlling the surface-enhanced Raman effect via the nanoshell geometry,i4pp/. Phys. Lett, 82, 257-259. 

SPECTROSCOPY OF POLYMER SURFACES USING THE SURFACE ENHANCED RAMAN EFFECT... 

Figure 2. Schematic drawing of a roughness feature inducing an enhanced Raman effect.

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