Preparation of SERS Substrates

The first SERS spectra were recorded on a roughened silver surface prepared by the method of EC-oxidation/reduction cycles [23]. By application of an oxidation potential to the metal electrode, the electrode was oxidized to soluble ions or an insoluble surface complex a reduction potential will then reduce these species at the surface, forming surface nanostructures. As silver is one of the most extensively studied SERS substrate materials, it is reasonable to take this as an example to illustrate the oxidation/reduction cycles procedure in detail [88]. 

Eigure 7.7 demonstrates the electrochemical roughening procedures for a Ag electrode in 0.1 M aqueous KCl electrolyte. The morphological evolution of the electrode surface is shown at the bottom of the figure. The electrode potential (the dashed line) is initially 

Smooth Ag electrode Insoluble Ag+ Cl- film Roughened Ag electrode 

It should be emphasized that the surfaces resulting from EC-oxidation/reduction cycling are randomly structured (Eigure 7.8a), and therefore they lack spot-to-spot and substrate-to-substrate reproducibility in their SERS response. Certainly, this ill-defined geometry is unfavorable for understanding the interfacial structure and maximizing SERS activity. 

The first ordered structures for SERS were reported during the early 1980s by Liao et al. [95,96], who obtained regularly ordered SERS substrates by depositing Ag particles over periodic arrays of silica posts that were fabricated by photolithography. Since the 1990s, with the rapid development in the field of nanofabrication, many ordered periodic arrays of nanoparticles for SERS have been made. 

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