Abstract
Oxygen and carbon monoxide adsorption on clean W(111) surfaces have been studied by angular resolved ESD emission (ESDIAD). In addition, the specimen could be characterized in situ with AES and LEED. Adsorption was performed at room temperature. The electron stimulated desorption yielded O + ions from the two investigated adsorption layers. Upon oxygen adsorption followed by subsequent annealing at least eight different ESDIAD patterns have been obtained. However, a convincing interpretation on the basis of the surface geometry can only be presented for three patterns produced without annealing as well as for one pattern at a very high annealing temperature. The difficulties are a consequence of complex structure changes which the surface undergoes in the intermediate annealing temperature range. This may influence the little known neutralisation probability of the desorbing ions. In this special case ESDIAD probably reflects in contrast to LEED a picture of some specific adsorption sites (minority species) and therefore, no clear correlation of the two techniques can be seen. ESDIAD from carbon monoxide shows four different patterns and supports the model of linear bonded CO molecules at room temperature with oxygen in the “standing up” position. At T > 900 K, CO starts to dissociate and results in similar ESDIAD patterns as obtained from O 2 adsorption.
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