Low energy electron diffraction and low energy electron microscopy microspot I/V analysis of the (4x4)O structure on Ag(111): Surface oxide or reconstruction?
Journal of Chemical Physics 127(13): -
A low energy electron diffraction (LEED) I/V analysis was performed of the (4x4) oxygen structure on Ag(111). Two data sets were used, one recorded with a conventional LEED system and a second with a low energy electron microscope (LEEM). The data sets agree well with each other, demonstrating that I/V structure analyses can be performed with the same quality with LEEM as with conventional LEED. The structure obtained confirms the recently proposed model that involves a reconstruction of the Ag(111) surface. Previous models based on a thin layer of Ag2O that had been accepted for more than 30 years are disproved. The reconstruction model contains two units of six triangularly arranged Ag atoms and a stacking fault in one half of the unit cell. The six O atoms per unit cell occupy sites in the trenches between the Ag-6 triangles. Small lateral displacements of the Ag atoms lift the mirror symmetry of the structure, leading to two nonequivalent groups of O atoms. The atoms of both groups are located approximately 0.5 A below the top Ag layer, on fourfold positions with respect to the top layer Ag atoms. Ag-O distances between 2.05 and 2.3 A are found. The oxygen atoms exhibit large static or dynamic displacements of up to 0.3 A at 300 K. (c) 2007 American Institute of Physics.