Structure and Stability of Underpotentially Depositied Layers on Au(111) Studied by Optical Second Harmonic Generation
Technical rept. no.5 Sep 89-Jun 91,
OREGON UNIV EUGENE DEPT OF CHEMISTRY
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This report details changes in the second harmonic optical response from Au111 during the underpotential deposition of Cu, Ag, Pb, and TI. The signal from Au111 exhibits a strong anisotropy that is assigned to a coupling of the SH photons with interband transitions. Underpotential deposition is used to form overlayers of foreign metals with precise control of the surface concentration of adatoms, and the participation of the d-like electronic states in binding of metal adsorbates is evidenced in the optical response. We compare the results from the Au111Cu and the Au111Ag interface with those from the 111 surface of the single crystal adsorbates and find that the results are consistent with the known electronic structure of the metals and geometric structures of the overlayers. In the case of lead and thallium deposition, a strong perturbation of anisotropic second harmonic signal is observed and attributed to the inability of the large adatoms to lattice match with the substrate. The consideration of domain effects is important for the optical results to be consistent with recent structural determinations.
- Physical Chemistry