Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

Molecular beam studies of trapping dynamics

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Molecular beam techniques have been used to probe the dynamics of trapping for a number of systems over a range of conditions. Specifically, we have determined the trapping probability in the limit of low coverage ξ0as a function of kinetic energy Eiand angle of incidence, θifor the adsorption of Ar and Xe on Pt( 111), of Ar on 2H-W(100) and of N2on W(100) and ethane on Ir(110)-(lx2).We find in all cases that ξ0approaches unity as Eitends to zero, falling at higher energies at a rate that depends on the function Eicosnθi. Values of n are found to range from 0 for the N2/W(100) system at 300 K, to 1.6 for Xe/Pt( 111) at 85 K. We have also determined the effect of surface temperature Txfor the case of Ar on Pt (111), and find that n tends to a value of 2 (corresponding to a dependence only on motion along the surface normal), as Tsdecreases to zero. © 1990, American Vacuum Society. All rights reserved.