Confocal drawback

The Fe-on-Ag and Ag-on-Fe approaches were subject to some drawbacks. In the former case, pinhole-free metal layers of a few monolayers thickness were difficult to deposit, they were unlikely to have the same crystal stmcture as bulk Fe, and they had insufficient stability over a wide potential range. With the Ag-on-Fe approach, it could not be excluded that species adsorbed at the Ag/Fe boundary contributed to the overall SERS response in a major fashion. As noted in Chapter 7, however, these concerns were minimized by advances in Raman instrumentation (i.e., the advent of confocal microscopy and the holographic notch filter) and the development of special oxidation/reduction treatments for roughening the electrode surfaces. 

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