| Abstract: | The electronic, chemical and physical properties of model bimetallic surfaces involving Cu, Ni and Pd have been investigated by means of X -ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), low energy electron diffraction (LEED) and CO chemisorption. The XPS results indicate that the electronic properties of supported Cu, Ni and Pd monolayers are perturbed with respect to the surface atoms of Cu(100), Ni(100) and Pd(100), in some cases significantly. The desorption temperature of the metal adlayer correlates very well with the electronic properties. This indicates that charge transfer is an important component of the cohesive bond at the surface. In general it is found that the formation of a metal-metal bond at the surface leads to a gain of electron density by the element initially having the greater fraction of empty states in the valence band. This behavior is completely opposite to that observed in bulk alloys. On the basis of these results a qualitative scale of surface electronegativity has been developed showing a trend that is very different from that found in three dimensional bulk alloys. It is also found that the electronic state of the bimetallic surface is an excellent indicator of its ability to chemisorb CO. The charge transfer determined by XPS is a measure of surface's ability to donate charge into the 2π* molecular orbital of CO which is primarily responsible f r determining the adlayer-CO bond strength. The induced shift in the adlayer's electronic properties upon CO adsorption is also a good indicator of the metal-CO bond strength. |
|---|