Continuous variation of iodine adlattices on Ag(111) electrodes: in situ STM and ex situ LEED studies

Abstract

The structure of the iodine adlattice formed on Ag(111) in aqueous solutions containing iodide ions has been determined as a function of the electrode potential by in situ scanning tunneling microscopy (STM) and ex situ low energy electron diffraction (LEED). In KI solutions buffered with KF-KOH at pH 10, continuous compression of the iodine adlattice from square (√3 × √3R-30°), via (√3 qR β° × √3R-30°), to (√3 × √3)R30° was observed as the electrode potential was increased; this was then followed by an abrupt phase transition into a rotated hexagonal (√3 r × √3 r)R(30° + α°) phase. Coadsorption of K was observed by Auger electron spectroscopy (AES) at potentials negative of that for the phase transition. In acid solutions (0.1mM HI) the continuous compression from (√3 × √3)R30°, via c( p × √3R-30°), into (√3 r × √3 r)R(30° + α°) was observed. The Moiré pattern observed for the (√3 r × √3 r)R(30° + α°) adlattice, as well as the flatness of other adlattices observed in STM images, is explained in terms of lattice registry on the basis of a “hard ball contact model”.