Sol–gel synthesis of Ge nanophases in silica

Elemental Ge nanophases are obtained in silica starting from a sol–gel synthesis. The process comprises the preparation of silica xerogel doped by Ge(IV), substituting for Si(IV) in the oxide network, followed by reduction and phase separation during the sintering process by reaction with H2 or CO. X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy show that reactions with H2 give rise in the porous silica network to nanometer-sized crystallization of elemental cubic germanium.