期刊
APPLIED PHYSICS LETTERS
卷 77, 期 25, 页码 4086-4088出版社
AMER INST PHYSICS
DOI: 10.1063/1.1334945
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We dispersed crystalline Si into a colloid of ultrasmall nano particles (similar to1 nm), and reconstituted it into microcrystallites films on device-quality Si. The film is excited by near-infrared femtosecond two-photon process in the range 765-835 nm, with incident average power in the range 15-70 mW, focused to similar to1 mum. We have observed strong radiation at half the wavelength of the incident beam. The results are analyzed in terms of second-harmonic generation, a process that is not allowed in silicon due to the centrosymmetry. Ionic vibration of or/and excitonic self-trapping on novel radiative Si-Si dimer phase, found only in ultrasmall nanoparticles, are suggested as a basic mechanism for inducing anharmonicity that breaks the centrosymmetry. (C) 2000 American Institute of Physics. [S0003- 6951(00)05452-8].
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