Preparation of well-defined surfaces at atmospheric pressure: Studies of structural transformations of I, Ag-Adlattices on Pt(111) by leed and electrochemistry

• Published in: Surface science 1984-01, Vol.146 (1), p.115-134
• Main Authors: Wieckowski, Andrzej, Schardt, Bruce C., Rosasco, Stephen D., Stickney, John L., Hubbard, Arthur T.
• Format: Article
• Language: English
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(84)90232-2

Pt(111) surfaces disordered by ion-bombardment or electrochemical oxidation were converted to well-defined, ordered states by annealing in iodine vapor at atmospheric pressure. A structure not obtainable in vacuum was formed, Pt(111)(3 3 × 9 3 )R30°-I , containing 0.62 I atoms per surfa ce Pt atom in a slightly distorted hexagonal array. The I-I interatomic distances in this structure, 0.33 and 0.36 nm, were less than the Van der Waals distance, 0.43 nm. Gentle heating of this structure under pure Ar yielded I 2 molecules, I atoms and a series of structures: Pt(111)(3 3 × 9 3 )R30°-I ▪( 3 × 3 )R30°-I ▪Pt(111) (clean surface). The Pt(111)( 7 × 7 )R19.1°-I adlattice proved to be identifiable from its distinctive electrochemical behavior in electrodeposition of Ag from aqueous solutions of AgClO 4, which consists of three prominent structural transitions. Kinematic calculations of the directions and qualitative intensities of the LEED beams at selected kinetic energies has led to proposed structures consisting of Ag atoms close-packed in registry with the three-fold sites of Pt but with I atoms substituted for Ag atoms at the ( 3 × 3 )R30° positions. Phase boundaries caused by reversals of the two packing sites of the 3 unit mesh at intervals 17 Pt unit vectors divide the surface into hexagonal antiphase domains.