Abstract
Ions liberated from an adsorbed layer by electron stimulated desorption are shown to have strongly focused and symmetric angular distributions. We have examined the Electron Stimulated Desorption Ion Angular Distributions (ESDIAD) for O+ ions desorbed from oxygen adsorbed on W(100); the ESDIAD patterns were displayed on a phosphor screen and photographed. ESDIAD patterns have been examined as a function of oxygen coverage and surface heat treatment; in most cases, patterns of 4-fold symmetry were observed. Dependent on oxygen coverage and sample temperature, the patterns were oriented with the 4-fold axes either parallel to or at 45° to the rows of surface atoms in the W(100) plane, as determined by LEED in the same apparatus. In addition, systematic variations in the appearance of the patterns (sizes and intensities of 4-fold "lobes") were seen for heat treatments at T\lesssim1000 K and may be related to the formation of surface oxides. We propose that the details of symmetry and intensity observed in ESDIAD patterns may provide new insights into the determination of adsorption sites and the nature of the bonding of atoms and molecules to surfaces.