Positron/positronium annihilation in nanocrystalline silicon thin films |
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Authors: | X. Zhao Y. Itoh Y. Aoyagi T. Sugano K. Hirata Y. Kobayashi T. Ohdaira R. Suzuki T. Mikado |
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Affiliation: | (1) The Institute of Physical and Chemical Research (RIKEN), Wako, 351-01 Saitama, (Japan);(2) National Institute of Materials and Chemical Research, 305 Tsukuba, Ibaraki, (Japan);(3) Electrotechnical Laboratory, 305 Tsukuba, Ibaraki, (Japan) |
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Abstract: | Positron and positronium annihilation investigations were applied to nanocrystalline silicon (nc-Si) thin films, for the first time. The nc-Si thin films with average grain diameters of 3–5 nm show intense blue luminescence at room temperature. The nanometer-sized Si crystallites formed in amorphous Si (a-Si) matrix give rise to this luminescence. Very highS-parameters up to 0.62 were observed in the as-grown a-Si thin film suggesting positronium formation in the a-Si layer. The average lifetime of the positrons in the a-Si was determined to be about 520 ps. TheS-parameters dropped significantly to 0.53 by crystallization of the thin film at 800 °C for 10 seconds, which was almost the same to the value observed in bulk Si (100) substrate. Further crystallization from 60 seconds to 1 hour showed smaller change in theS-parameters than that from the a-Si to 10 seconds. The large change in theS-parameters due to the annealing might be caused by the formation of Si nanocrystallites in a-Si matrix suggesting that positron is a sensitive probe for structural investigations of the nc-Si materials. |
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