New mechanism for positronium formation on a silicon surface.
Phys Rev Lett
; 106(13): 133401, 2011 Apr 01.
Article
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| MEDLINE
| ID: mdl-21517381
ABSTRACT
We describe experiments in which positronium (Ps) is emitted from the surface of p-doped Si(100), following positron implantation. The observed emission rate is proportional to a Boltzmann factor exp{-E(A)/kT}, which is dependent on the temperature T of the sample and a characteristic energy E(A)=(0.253±0.004) eV. Surprisingly, however, the Ps emission energy has a constant value of â¼0.16 eV, much greater than kT. This observation suggests the spontaneous emission of energetic Ps from a short-lived metastable state that becomes thermally accessible to available surface electrons once the positron is present. A likely candidate for this entity is an electron-positron state analogous to the surface exciton observed on p-Si(100) c(4×2) by Weinelt et al. [Phys. Rev. Lett. 92, 126801 (2004)].
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Phys Rev Lett
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2011
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Article