Structures of adsorbates and their interaction with metal overlayers grown on a flat and a stepped Cu(111) surfaceCu(111)

Abstract

The interaction of Fe overlayers with CO on a stepped Cu(111) surface was investigated by thermal desorption spectroscopy and low energy electron diffraction. The Cu surface cut 8° off (111) plane in direction [11$\overline{2}$] has regularly ordered steps in direction [1$\overline{1}$0] and approximately 8 atoms-wide terrace planes. CO titration method was used to probe the bare Cu surface that was not covered with Fe overlayers after Fe deposition. According to the results, CO desorption from steps disappears much faster than that from terraces as the Fe coverages increase at the substrate temperatures of 110K and 200K. However, at room temperature, the ratio between CO desorption from steps and terraces increases steadily with increasing Fe coverages. Since Fe atoms grown on the surface were reported to prefer steps to terraces from very submonolayer coverages even at room temperature, the observed results were explained with the size distribution of Fe islands as a function of substrate temperatures. CO desorption from Fe overlayers (Fe-α) was found to give additional informations on the facets of 3-dimensional Fe islands which varied their shapes with increasing Fe deposition temperatures. When oxygen is exposed to the stepped Cu(111) surface at the substrate temperature lower than 200K, CO desorption spectra and LEED patterns suggest that oxygen adsorbs on the terraces as well as the steps of the Cu substrate without serious changes in the periodic step arrangements. At room temperature, however, LEED results indicate that the adsorbed oxygen atoms induce some changes in the regular surface step structures, which is attributed to be the result of step migrations. Fe grown on the O pre-adsorbed Cu surfaces seems to incorporate oxygen into the Fe islands to form Fe oxide. Thermal and photoinduced decomposition of $Fe(CO)_5$ adsorbed on the 8°-off Cu(111) surface at 100K and room temperature were investigated using TDS and LEED. At low $Fe(CO)_5$ exposures, ...