Positron dynamics in surface-charged solid argon
- Institute of Physics and Astronomy, University of Aarhus, DK-8000 Arhus C (Denmark)
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
Studies have been made of the reemission of positrons incident at low energies upon solid argon to which electric fields were applied by charging an overlayer of molecular oxygen. An enhancement in positron reemission was observed which reached a maximum for an applied field of around 7 kV mm{sup {minus}1}. At this field strength the same yield was observed for implantation energies ranging from 1 to 10 keV, consistent with enhancement due to field-induced positron drift to the exit surface. At higher electric fields, the observed gradual decrease in enhancement was attributed to the heating of the positron energy distribution above the positronium formation threshold. Quantitative agreement with our experimental results has been obtained using a Monte Carlo simulation from which estimates for the positron diffusion length and mobility of 1.7(+2.0,{minus}0.4) {mu}m and 4.7(+2.9,{minus}0.4){times}10{sup {minus}3} m{sup 2} V{sup {minus}1} s{sup {minus}1}, respectively, have been derived. This model was also able to successfully reproduce previous results obtained using surface-charged argon {beta}{sup +} moderators. An abrupt and almost complete reduction in positron reemission was observed for applied surface potentials above a value which showed a weak dependence on film thickness.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 122356
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 16 Vol. 52; ISSN 0163-1829; ISSN PRBMDO
- Country of Publication:
- United States
- Language:
- English
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