Abstract
Electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED) have been used to study the adsorption of oxygen on the stepped Ni(510) face at a surface temperature around 100 K. As the coverage increases three different adsorption states for the oxygen atoms are observed; initially a low coverage (θ < 0.25) layer of oxygen adsorbed in the hollow sites on the terraces is established, secondly also step sites get occupied, and finally c(2 × 2) like oxygen overlayers are formed on the, probably microfaceted, terraces. Vibrational losses at 51, 62 and 44 meV, respectively, are related to these three adsorption states. Also coadsorption of oxygen and hydrogen has been studied. The Ni(510) surface, pre-exposed to different amounts of oxygen, was saturated with hydrogen. When only terrace sites are occupied with oxygen, both atomic and molecular hydrogen adsorption occur. The H atoms adsorb both in step sites and on the terraces while the H 2 molecules chemisorb at step edge sites. When the step sites are saturated with oxygen no hydrogen adsorption is observed any longer.
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