The fluorescence extended X-ray absorption fine structure (EXAFS) technique was used to study the local structure of Ge nanocrystals embedded in SiO2 matrix

which were synthesized by the magnetron sputtering co-deposition. It is revealed that in the as-prepared samples

Ge atoms mainly exist in the form of amorphous phases of Ge and GeO2. The sample with Ge mole fraction of 25% is mainly composed of the GeO2 phase. Upon annealing at 1073 K

Ge nanocrystals are formed. In the sample of 25% Ge (mole fraction)

Ge nanocrystals come from amorphous Ge phase; while in the sample of 60% Ge (mole fraction)

Ge atoms come from both GeO2 and amorphous Ge phase. A further analysis of the sample containing 60% Ge (mole fraction) shows that about 20% GeO2 (mole fraction) is turned into Ge nanocrystals due to the reduction reaction with Si atoms coming from the substrate.