Electronically stimulated desorption from physisorbed layers on metal surfaces: Kinetic-energy distributions of desorbed neutral atoms

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Abstract
Previous work on the calculation of kinetic-energy distributions of neutral adsorbate atoms or molecules from physisorbed layers on clean metal surfaces is extended and applied to rare-gas layers. In agreement with other authors, the basic mechanism is assumed to be ionization to a more strongly bound state, acceleration towards the surface, and reneutralization after sufficient kinetic energy has been acquired by the particle to overcome the residual ground-state van der Waals attraction after reflection at the surface. A classical and a quantum-mechanical model are developed and their results are compared. In the regimes where both calculations are possible, rather good agreement is obtained. An improvement over fitting of the experimental energy distribution is reached by introduction of a direct inversion procedure of the experimental data. Thus we can map out the parameter space for reneutralization compatible with physical considerations. Existing data on energy distributions can be well reproduced in this framework, by fitting or inversion. However, if known values for the total desorption yields are also considered, the only neutralization parameters compatible with both types of data are markedly unphysical (extremely strong distance dependence of neutralization rate with very high preexponentials). Some possible explanations for the discrepancies are considered, one of which (energy loss of the accelerated ions via friction) leads qualitatively to the correct behavior.