Nonthermal plasma synthesis of faceted germanium nanocrystals

Low-pressure plasmas are known for their ability to synthesize nanoparticles via gas-phase nucleation. While in the past this particle formation has often been considered from the viewpoint of a contamination problem in semiconductor processing, we here describe a low-pressure plasma that enables the synthesis of faceted germanium nanocrystals. The germanium nano-crystals are generally single crystals without any planar defects such as twin boundaries. A change in the morphology with particle size is observed. Small germanium particles up to about 30 nm in size are mostly cubes with (100) crystal facets. Larger crystals between 30-60 nm are primarily cuboctahedrons. Even larger nanocrystals are mainly spherical. The shape evolution is interpreted in terms of the equilibrium shape of hydrogen-coated germanium crystals. Possible applications of these crystals are discussed.