DESORPTION OF METAL ATOMS WITH LASER-LIGHT - MECHANISTIC STUDIES

Results on laser-induced desorption of metal atoms from small metal pa rticles are presented. Experiments have been performed on sodium, pota ssium, and silver particles supported on a LiF(100) single-crystal sur face under ultrahigh vacuum conditions. Measurements include the deter mination of the desorption rate as a function of laser wavelength, las er intensity, average particle size, and substrate temperature, the de termination of the kinetic energy of the desorbed atoms, the investiga tion of the optical spectra of the supported metal particles, and the study of the influence of adsorbate molecules on the desorption rate. Furthermore, theoretical extinction and absorption spectra of the meta l particles have been calculated with the classical electrodynamical M ie theory as a function of average particle size and excitation wavele ngth. Also, the radial electric field at the particle surface was comp uted. The results of the experiments and theoretical calculations are combined to give a consistent picture of the mechanism of metal-atom d esorption by electronic excitation with laser light. A realistic surfa ce potential from which the atoms escape and nonlocal optical effects are taken into account. The latter introduce additional absorption cha nnels by the formation of electron-hole pairs in the surface layer of the particle which relax into antibonding states before desorption occ urs. Finally, the mechanism is discussed in the light of similar pheno mena observed for thin metal films. Possibilities for future work are outlined.