An Investigation of Underpotentially Deposited Thallium of Silver (111) by In-Situ Surface X-Ray Scattering
PUERTO RICO UNIV RIO PIEDRAS DEPT OF PHYSICS
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Using in-situ surface x-ray scattering, we have investigated the atomic structure, the stability, and the dependence of the structure on electrode potential for electrochemically deposited T1 monolayers and bilayers on Ag 111. The layers were formed by underpotential deposition UPD at electrode potentials positive of the reversible potential for bulk T1 deposition. At potentials between -475 and -680 mV vs. AgAgC1, the T1 deposit forms an incommensurate, hexagonal two dimensional 2D monolayer that is compressed relative to bulk T1 by 1.4-3.0 and rotated from the Ag and roll direction by omega 4-5 deg. The structure of the monolayer does not change over at least 24 hours the longest we waited. From diffraction scans of the T1 Bragg rods, we find that the in-plane and vertical root-mean-square displacement amplitudes are 0.36 or - 0.05 lambda and 0.46 or - 0.1 lambda, respectively. The monolayer structure is the same as that of vapor deposited T1Ag 111, and this shows that the interaction between the solvent molecules and the T1 adatoms does not influence the monolayer structure. Since the monolayer has a structure that is about the same as the closest packed planes of bulk T1, we deduce that the adatom-adatom interactions are the most important structure determining forces. The compression of the monolayer compared to bulk T1 is explained in terms of effective medium theory.
- Physical Chemistry