Stable, freestanding Ge nanocrystals

Freestanding Ge nanocrystals that are stable under ambient conditions have been synthesized in a two-step process. First, nanocrystals with a mean diameter of 5 nm are grown in amorphous SiO2 by ion implantation followed by thermal annealing. The oxide matrix is then removed by selective etching in diluted HF to obtain freestanding nanocrystals on a Si wafer. After etching, nanocrystals are retained on the surface and the size distribution is not significantly altered. Freestanding nanocrystals are stable under ambient atmospheric conditions, suggesting formation of a self-limiting native oxide layer. For freestanding as opposed to embedded Ge nanocrystals, an additional amorphouslike contribution to the Raman spectrum is observed and is assigned to surface reconstruction-induced disordering of near-surface atoms. (c) 2005 American Institute of Physics.