Surface enhanced Raman spectroscopy: A re-examination of the role of surface roughness and electrochemical anodization

Adatom Hypothesis as a Predominant Mechanism of Surface Enhanced Raman Scattering: A Review of Experimental Argumentation

“…The absence of enhancement of RS spectra for pyridine was registered also on mechanically polished silver in [46] (as opposed to numerous reports about observation of SERS, albeit less intensive, on mechanically polished silver [1,4,5,14,42,47]). Nor was SERS discovered at electrodes subjected to ER and then cathodically polarized for a long time at potentials E ≤ -1.4 V vs. normal hydrogen electrode (NHE) [48] when nonequilibrium silver adatoms, which are SERSactive adsorption centers, which form a complex with pyridine molecules, disappear [42,49] (and this observation is inconsistent with available information about the presence of "residual" SERS after such a cathodic treatment [49,50]).…”

“…Upon covering the surface at levels eluding assay by traditional methods, adatoms are capable of providing for quite measurable values of G . It is precisely this circumstance that could have been the reason for the results reported in [1,4,5,42,47,51]. We stress that enhancement of RS spectrum for pyridine was not discovered at stepwise faces (540) of single-crystal silver [52] when using the surface preparation procedure reported in [44], nor was it discovered on silver faces (521) or (987) containing fractures of steps or "kinks" (see paper by Campion and Mullins in [36]).…”

“…It was demonstrated, however, that even a single ORC in the case of silver in conditions close to these ensured observation of SERS from pyridine at silver [3]. Subsequent ER regimes were various: single and periodic rectangular anodic pulses of potential of different length [1,47,[53][54][55][56]; fast and slow linear potential scan with excursion to the surface oxidation or dissolution region [42,47,49,53,57] (see also papers by Benner et al in [28], Philpott et al and Owen et al in [32]) and combined regimes [57,58]. Shown was that ER under a laser beam in solutions containing anions that form salts with silver which are subjected to photoexcitation or even photolysis at excitation light wavelengths λ e (at first stages it was radiation of an ion argon laser at λ e = 514.5 nm that was used most frequently) ensured values of G that were several times (especially in the first cycle of ER) the "dark" ER [59][60][61] (see also papers by Philpott et al and Owen et al in [32]).…”

Cooperative Near‐Field Surface Plasmon Enhanced Quantum Dot Nanoarrays

“…Surface roughness appears to play a signifi cant role in fl uorescence enhancement in these lithographically prepared arrays. Although surface roughness is widely studied in the SERS literature, [51][52][53] its role is discussed less frequently in the realm of fl uorescence enhancement. Our data, both with the annealed substrates and colloidally roughened substrates, confi rm that surface roughness is an important variable to consider when evaluating the performance of lithographically defi ned plasmonic nanostructures in fl uorescence applications.…”

Surface enhanced Raman scattering from silver electrodes

“…Although with any surface analysis technique, very careful and thorough cleaning procedures must be followed, there still may exist trace amounts of contaminants in the electrochemical cells and on the silver electrodes as the systems are assembled. Thus, the anodization process, by reforming the silver surface, acts as an in situ cleaning process (47). However, there are other types of in situ electro chemical cleaning processes which do not result in a SERS signal.…”