Substrate preparation roughening

In order to investigate molecules adsorbed at the solid-liquid interface roughened electrode surfaces or metal colloids in solution (sols) are prepared. For investigations of the solid-gas or solid-vapour interface several methods are available to produce metal island films on SERS-active substrates. 

Further enhancement of the SERS can be achieved through precise control over the parameters at the metal particle size scale [10] Most SERS-active substrates were made from pure metallic nanostructures such as metal nanoparticles [33-35], metal particle arrays [5], roughened metal surfaces [36], or a combination with metal nanostructures and other nanomaterials [17, 18, 29, 37-39]. Recently, many strategies have shown the adsorbation of molecules on the surface of Ag and Au substrates for SERS applications [40]. SERS-active Ag nanostructures substrates are required to satisfy certain conditions with good reproducibility and stability [39]. For this reason, it is indispensable to develop and optimize the methods to prepare the SERS-active Ag substrates [41]. 

Surface Roughening - In adhesive bonding, a commonly used surface preparation technique in which the substrate surface is mechanically abraded. The roughened surface increases bondability by dramatically increasing the number of sites available for mechanical interlocking. 

To prepare highly SERS-active substrates, proper surface roughening procedures are necessary. 

Fig. 19 Schematic depictions of (a) the preparation of a cobalt pyrite (C0S2) film electrode via the thermal sulfidation of a 100 nm thick cobalt film deposited over a titanium adhesion layer on a roughened borosilicate glass substrate by electron-beam evaporation and (b) the incorporation of an as-synthesized C0S2 film on glass into a CdS/ CdSe-sensitized thin-layer liquid-junction quantum dot-sensitized solar cell (QDSSC) filled with sulfide/polysulfide electrolyte to demonstrate the high QDSSC performance enabled by the C0S2 counter electrode. Reproduced from ref. 167 with permission from the American Chemical Society.

SERS does, however, have some limitations. For the SERS effect to occur, the analyte needs to be adsorbed onto or in close proximity to the roughened metal surface, and only a few metals have so far been shown to be efficient at providing surface enhancement. SERS intensities are also dependent on the roughness of the metal surface, and there are significant problems associated with the preparation of reproducible substrates with uniform roughness features. The spectra obtained are also dependent on the orientation of the molecule on the metal surface, and vibrations with little to no intensity in normal Raman scattering can become relatively intense. This can in some cases make it difficult to identify the analyte positively. Eurther, contamination can also be a problem. Since SERS is very sensitive, it is possible that very small amounts of a contaminant can be enhanced, and if the analyte to be considered does... 

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]. 

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