Abstract
In order to examine the role of atomic steps and defects on electron stimulated desorption (ESD) phenomena, we have studied the adsorption of oxygen on a polyhedral tungsten crystal containing a W(110) flat and 4 flats having orientations 6° and 10° off the (110) plane with rows of steps parallel to the [100] and [110] directions. Upon adsorption at 300 K, there is little or no ESD O + emission from the oxygen-covered (110) plane. In contrast, the stepped surfaces yield intense O + emission normal to the terraces and in “downstep” directions, as seen using electron stimulated desorption ion angular distributions (ESDIAD). The presence of atomic steps has a major influence on sticking probability, saturation oxygen coverage and the ESDIAD patterns at all adsorption temperatures in the range 100 K to ⪆1400 K. Adsorption at low coordination sites appears to be a key factor in producing high ESD ion yields.
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