STUDIES OF CHEMICALLY MODIFIED MOLYBDENUM(100) SURFACES USING PHOTOELECTRON SPECTROSCOPIES AND PHYSISORBED XENON AS A PROBE (CHEMISORPTION)

The properties of chemically modified, single crystal molybdenum surfaces were investigated using x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopies. The effect of modifier electronegativity on the electronic and chemical properties of the Mo(100) surface was studied using adsorbed oxygen (high electronegativity) and boron (intermediate electronegativity) as modifiers. A technique was developed to obtain a measure of surface polarizability using XPS measurements of the Auger parameter for physisorbed xenon. The polarizability strongly decreases between 1.0-1.7 monolayers of adsorbed oxygen due to a phase transition from chemisorbed oxygen to a surface oxide in this coverage range. This correlates with a decrease in the chemical reactivity of the surface toward various small molecules above 1.0 monolayers oxygen. These effects are attributed to a large degree of charge transfer from molybdenum to oxygen. Boron-modified surfaces were synthesized by decomposition of diborane on the surface. The B/Mo interaction was investigated as a function of both coverage and anneal temperature. Unlike the O/Mo(100) system, very little charge transfer occurs between boron and molybdenum and boron does not diminish surface reactivity except by blocking adsorption sites.