Sputtering of thin benzene and polystyrene overlayers by keV Ga and C-60 bombardment

The mechanisms of ion-stimulated desorption of thin organic overlayers deposited on metal substrates by mono- and polyatomic projectiles are examined using molecular dynamics (MD) computer simulations. A monolayer of polystyrene tetramers (PS4) physisorbed on Ag {111} is irradiated by 15 keV Ga and C-60 projectiles at normal incidence. The results are compared with the data obtained for a benzene overlayer to investigate the differences in sputtering mechanisms of weakly and strongly bound organic molecules. The results indicate that the sputtering yield decreases with the increase of the binding energy and the average kinetic energy of parent molecules is shifted toward higher kinetic energy. Although the total sputtering yield of organic material is larger for 15 keV C-60, the impact of this projectile leads to a significant fragmentation of ejected species. As a result, the yield of the intact molecules is comparable for C-60 and Ga projectiles. Our data indicate that chemical analysis of the very thin organic films performed by detection of sputtered neutrals will not benefit from the use Of C-60 projectiles. (c) 2006 Elsevier B.V. All rights reserved

Spectroscopic behavior of halogen photodesorption from alkali halides under UV and VUV excitation

The photostimulated desorption yield of neutral halogen atoms from KI, KBr, and RbI at several temperatures has been measured in the photon energy range between 5 and 30 eV using synchrotron radiation and quadrupole mass spectrometry. The features observed in the desorption yield are slightly correlated with the structures of the absorption spectra of each investigated material. The behavior of the halogen desorption yield is analyzed in the frame of inelastic electron-electron scattering processes, in close analogy with data available from the total photoelectron yield and the luminescence yield. The role played in the desorption mechanism by fundamental excitations, such as valence exciton creation and band-gap electron-hole excitation, is discussed

Photon stimulated desorption from alkali halide surfaces at near threshold energies

Desorption processes induced in alkali halides by photons of synchrotron radiation (of energy 5-20 eV) have been investigated by means of quadrupole mass spectroscopy. The relative yields and angular characteristics of alkali and halogen atoms emitted from (100) surfaces of KI and RbI crystals were measured as a function of the photon energy and the sample temperature. For comparison, analogous measurements were performed with a 1 keV electron beam. In the latter case the relevant desorption processes are already better understood. We have found that both the fundamental exciton and the fundamental gap excitations result in alkali and halogen desorption with the same angular distributions. This leads to the conclusion that dynamic desorption processes, pronounced for electron excitation, are inefficient during desorption stimulated by photons with near threshold energies. It is argued that such a difference can be understood by taking into account different selection rules, and differences in excitation depth and excitation density distribution for photon- and electron-induced processes