On the structure of amorphous germanium and silicon

The simple microcrystallite model is used to calculate the diffraction and radial distribution functions for a variety of tetrahedrally coordinated crystal structures: diamond, wurtzite, Ge III and Si III — two high-pressure polytypes of Ge and Si — and two clathrate structures based on pentagonal dodecahedral units. Comparison with data for sputtered amorphous Ge suggests that the simple microcrystallite model is inadequate to fit diffraction data. A statistical or combination microcrystallite model may be more promising. Recent electron microscopic investigations of Rudee and Howie are also discussed.