Preparation, structural characterization, and properties of atomically clean surfaces

Abstract

My first research on secondary electron emission showed that some secondary electrons from the surface of a solid had energies comparable to that of the incident electrons, i.e., they were elastically scattered incident electrons, in disagreement with results of several previous workers in this field. Several maxima in the secondary emision versus incident energy curves were related to growth of the individual crystals, caused by heat‐treatment. Subsequent to the discovery of low energy electron diffraction (LEED) by Davisson and Germer, I began a series of LEED investigations from single crystals of several elemental metals, and found many complicated features, such as fine structure of diffraction beams, which were sensitive to small changes in angles of incidence. Because Ti and Ge crystals could not be cleaned in UHV by heating alone, we were led to a method of producing atomically clean surfaces by argon ion bombardment and subsequent anneal to remove surface damage. This technique led to the discovery that atomically clean semiconductors, having a diamond‐type lattice structure such as Ge and Si, have an altered surface structure different from that of the bulk lattice, and that this structure is removed by adsorption of a monolayer of oxygen. Investigations were made of adsorption and surface reactions by the combined use of LEED, work function and mass spectrometer measurements in a single unit. Discovery was made of place exchange of oxygen and nickel atoms at Ni(100) to form metallic Ni3O as a precursor of NiO, a semiconductor. Other investigations followed on epitaxy, work functions of different faces of single crystals, effect of mechanical strain and defect density on work function, inelastic diffraction, crystals cleaved in UHV, bombardment damage, reflection of very low energy electrons, the (00) LEED beam intensity at normal incidence, alloy catalysts, surface recombination velocity, adsorption by radioactive tracer, H2–D2 exchange, and effect of lattice defects on chemisorption, oxidation and catalysis.