Nonthermal plasma synthesized freestanding silicon-germanium alloy nanocrystals.

The composition, structure, light emission and oxidation kinetics of Si(1-x)Ge(x) alloy nanocrystals ( approximately 3 nm in diameter) synthesized by nonthermal plasma have been investigated. It is found that the synthesized nanocrystals are neither a mixture of Si nanocrystals and Ge nanocrystals nor Si-Ge (Ge-Si) core-shell nanocrystals. The H coverage at the surface of Si(1-x)Ge(x) nanocrystals decreases with the increase of the Ge atomic fraction. The incorporation of Ge enhances the oxidation of Si(1-x)Ge(x) nanocrystals when the atomic fraction of Ge is <0.5. No shift in photoluminescence from hydrosilylated Si(1-x)Ge(x) nanocrystals is observed when the atomic fraction of Ge varies between 0 and 0.1, indicating that the bandgap of Si nanocrystals is similar to that of Ge nanocrystals at a nanocrystal size of 3 nm.

Air-stable full-visible-spectrum emission from silicon nanocrystals synthesized by an all-gas-phase plasma approach.

A novel dual-plasma system has been developed to combine the synthesis of silicon nanocrystals (Si-NCs), the etching to controllably tailor the Si-NC size, and the surface functionalization of Si-NCs into one simple all-gas-phase process. Si-NCs are synthesized in SiH(4)-based plasma; they then travel through CF(4)-based plasma, where Si-NCs are etched and passivated by C and F. The resulting Si-NCs exhibit air-stable emission across the full visible spectrum. Structural and optical characterization indicates that the emission in the red-to-green range is based on the recombination of quantum-confined excitons in Si-NCs, while the blue emission originates from defect states. The quantum yields of stabilized photoluminescence from Si-NCs range from 16% at the red end to 1% at the blue end.

Fluorine in silicon: diffusion, trapping, and precipitation.

The effect of vacancies on the behavior of F in crystalline Si has been elucidated experimentally for the first time. With positron annihilation spectroscopy and secondary ion mass spectroscopy, we find that F retards recombination between vacancies (V) and interstitials (I) because V and I trap F to form complexes. F diffuses in the V-rich region via a vacancy mechanism with an activation energy of 2.12+/-0.08 eV. After a long annealing time at 700 degrees C, F precipitates have been observed by cross-section transmission electron microscopy which are developed from the V-type defects around the implantation range and the I-type defects at the end of range.