Surface-enhanced Raman scattering detectors

An early example of surface Raman without field enhancement is shown in Figure 13.7. This measurement predated the development of CCD detectors and represents a major achievement in terms of sensitivity (12). The adsorption of nitrobenzene on a well-defined nickel surface was carried out in UHV then Raman scattering was observed with a single spectrograph and an intensified Vidicon detector. Unenhanced spectra were obtained from 7.5 x lO molecules cm of nitrobenzene (1.1 x 10 " mol cm ), corresponding to a submonolayer. Examples of surface Raman spectroscopy with resonance enhancement include monolayers of phthalocyanines on gold (17) and ordered graphite (18), and multilayers of metalloporphyrins (19). 

With increasing sensitivity of detectors, the detection of unenhanced surface Raman scattering becomes a possibility, and if this is achieved a wide range of effects can be investigated. In particular the determination of adsorbate orientation from depolarisation ratios and the angular dependence of the Raman signal will be possible. Currently, such measurements only serve as a means of investigating the enhancement mechanism. 

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