Active Sites and the Quenching of SERS

Another possibility for quenching SERS-active atomic-scale sites in the electrochemical environment is by underpotential deposition of metals such as T1 and A very small underpotential coverage of deposited Tl, ca. 

FIGURE 1. SERS intensity versus a triangular sweep potential for the 1006-cm band of pyridine as a function of switching potential and scan rate. Solution 0.05 M pyridine and 0.1 M KCl. (a) Intensity versus potential (/-V) curves shows no hysteresis for a switching potential of -0.9 V versus SCE at a scan rate of 100 mV s. (b) /- V curve shows hysteresis is observed for a switching potential of -1.2 V versus SCE at a scan rate of 5 mV s V At slower scan rates, still more hysteresis develops. (c) 7-V curve shows no hysteresis for a switching potential of -1.2 V versus SCE at a scan rate of 500 mV s  

Additional evidence for atomic-scale active sites from SERS on Ag are the deposition experiments of Furtak and coworkers and those of Marinyuk et In the former experiment, monolayer deposits of Ag on Au show SERS from pyridine under excitation with blue laser light. An Au electrode is similar to a Cu electrode in that it only gives SERS with red laser excitation thus with blue light it would be impossible to observe SERS of pyridine on Au. In the latter experiment,SERS is observed after monolayer amounts of Ag are deposited on Pt, a surface which does not normally show SERS in the electrochemical environment. 

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