Theory of positronium formation and positron emission at metal surfaces

Journal Article · Mon Sep 01 00:00:00 EDT 1980 · Phys. Rev., B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.22.2226· OSTI ID:5051287

Nieminen, R M; Oliva, J

The probability for a positron (e/sup +/) incident upon a metal surface either to be converted into a positronium atom (Ps) which leaves the surface or to be reemitted as a bare e/sup +/ is calculated using a model which goes considerably beyond that used in a previous calculation. The Ps conversion and e/sup +/ emission process proceeds in three stages: implantation, thermal diffusion from the characteristic stopping distance to the surface, and electron capture with bare e/sup +/ escape. The stopping distance and its rms deviation are calculated now including both the effect of elastic positron--ion-core scattering (in addition to inelastic e/sup +/-- conduction-electron and e/sup +/-phonon scattering) and finite temperature corrections in the e/sup +/-phonon scattering. Given a thermal e/sup +/ near the surface, we examine the probabilities of the following processes: direct e/sup +/ ..-->.. Ps conversion (calculated within a simple ''resonant-level'' model), e/sup +/ trapping into the image potential induced surface state, direct e/sup +/ escape into vacuum (perturbation theory), and Ps formation via e/sup +/ detrapping from the surface state. Overall conversion and emission efficiencies are calculated by solving an appropriate diffusion equation with boundary conditions set by the branching ratios for the above surface processes. The temperature and incident energy dependence of our results for final Ps conversion and e/sup +/ emission efficiency are compared with experiment.

• Research Organization: Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853
• OSTI ID: 5051287
• Journal Information: Phys. Rev., B: Condens. Matter; (United States), Vol. 22:5
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
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POSITRON COLLISIONS
POSITRONIUM
PARTICLE PRODUCTION
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EXCITED STATES
POSITRON REACTIONS
SURFACE PROPERTIES
COLLISIONS
ELEMENTS
ENERGY LEVELS
LEPTON REACTIONS
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