Nanocrystalline Ge synthesis by the chemical reduction of hydrothermally grown Si0.6Ge0.4O2

Abstract

Previously, we have reported the use of high pressure oxidation techniques for the growth of compositionally congruent oxides from Si1−xGex. We have now used this technique as part of a two-step process of oxidation at 25 MPa and 475°C followed by reduction in 0.1 MPa (1 atm) H2 at 700-850δC for the synthesis of nanocrystalline Ge precipitates. Using transmission electron microscopy, we show that the proposed method produces a dispersion of fine (<10 nm) precipitates of Ge embedded in an SiO2 matrix. The structure of the oxide prior to reduction with H2 was investigated with Fourier transform infrared spectroscopy which reveals SiO2, GeO2, SiO, Si-O-H, and Ge-O-H bonding states in the glass. In this paper, we discuss the thermodynamics and kinetics of both the hydrothermal oxidation technique and the proposed Ge nanocrystalline synthesis process.