ANGULAR, ENERGY, AND POPULATION-DISTRIBUTIONS OF NEUTRAL ATOMS DESORBED BY KEV ION-BEAM BOMBARDMENT OF NI(001)

Multi-photon resonance ionization, time-of-night mass spectrometry and imaging techniques have been employed to measure the polar-angle, kin etic energy, and population distributions of Ni atoms desorbed from 5 keV Ar ion bombarded Ni{001}. The measured angle- and energy-resolved intensity maps of the sputtering yield provide a set of data that can be used to examine the detailed interactions between the particles of the solid surface during the sputtering event. The results show a cons iderable degree of anisotropy associated with both the ejection angle as well as the crystallographic direction. In order to have an underst anding of the interactions of the desorbed particles with the surface, molecular dynamics simulations of the ion-induced sputtering event ar e performed. The agreement between experimental and computer simulatio n results is excellent. Measurements performed on excited states of sp uttered Ni show that the valence electron shelf structure is an import ant factor in determining the angle-integrated kinetic energy distribu tion while the magnitude of the excitation energy is of secondary impo rtance. Population distribution among different electronic states is o btained through two sets of measurements performed on different instru ments. Both measurements employ the same resonant ionization schemes a nd laser fluences. The results show that the a(3)D(3) and a(3)D(2) sta tes are more heavily populated than is predicted by a Boltzmann-type d istribution.