Cassidy, DB; Hisakado, TH; Tom, HWK; Mills, AP; (2011) New mechanism for positronium formation on a silicon surface. Physical Review Letters , 106 (13) , Article 133401. 10.1103/PhysRevLett.106.133401.

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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/kT}, which is dependent on the temperature T of the sample and a characteristic energy E=(0.253±0.004)eV. Surprisingly, however, the Ps emission energy has a constant value of ∼0.16eV, 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. © 2011 American Physical Society.

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