IN-SITU OPTICAL 2ND-HARMONIC GENERATION STUDIES OF ELECTROCHEMICAL DEPOSITION OF TELLURIUM ON POLYCRYSTALLINE GOLD ELECTRODES

The electrodeposition of tellurium (Te) on polycrystalline gold electr odes was studied using in situ optical second harmonic generation (SHG ) at two different excitation wavelengths. On excitation at 1064 nm, t he SH signal decreased dramatically with the first Te underpotential d eposition (upd) and increased slightly with the second upd and the bul k deposition of Te. There was a linear correlation between the square root of the SH intensity from the surface and the surface coverage of Te, although the proportionality constant of this correlation for the first Te upd was different from those for the second upd and bulk depo sition. This is possibly because of the stronger interaction of the fi rst upd layer of Te than the second and bulk layer of Te with the subs trate surface. However, on excitation at 585 nm, the behavior of the S H signal was more complicated, especially during the desorption proces s of the first Te monolayer. An increase in the SH intensity was obser ved with the first Te upd, but this increase in SHG still continued in the potential region in which no deposition of Te occurred. These res ults are interpreted by considering the existence of an optical resona nce at the Au surface covered with a Te monolayer.