Reichelt, R.; Günther, S.; Wintterlin, J.; Moritz, Wolfgang; Aballe, L.; Mentes, T.O.
Low energy electron diffraction and low energy electron microscopy microspot IV analysis of the (4×4) O structure on Ag(111): Surface oxide or reconstruction?
In: Journal of Comparative Physiology A - Neuroethology, Sensory, Neural, and Behavioral Physiology, Vol. 127, No. 13
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A low energy electron diffraction (LEED) IV analysis was performed of the (4×4) 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 IV 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 Ag2 O 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 Ag6 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 Å 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 Å are found. The oxygen atoms exhibit large static or dynamic displacements of up to 0.3 Å at 300 K.