Citation:
Hakala , M , Puska , M J & Nieminen , R M 1998 , ' Momentum distributions of electron-positron pairs annihilating at vacancy clusters in Si ' PHYSICAL REVIEW B , vol 57 , no. 13 , pp. 7621-7627 . DOI: 10.1103/PhysRevB.57.7621
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Abstract:
We report calculations of momentum densities of electron-positron pairs annihilating at various vacancy clusters in Si. The densities integrated along one direction, i.e., those corresponding to the spectra measured by the two-dimensional angular correlation of the annihilation radiation method, are shown to be isotropic if the positron is captured by a small vacancy cluster. The densities integrated along two directions correspond to the one-dimensional angular-correlation distribution or the Doppler-broadened annihilation radiation line shape. The characteristic narrowing of these one-dimensional distributions at vacancy clusters is demonstrated. The line-shape parameters S and W describing mainly the annihilations with valence and core electrons, respectively, are calculated and compared quantitatively with experimental data. We find a systematic increase in the S and a decrease in the W parameter as the size of the vacancy increases.
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