Diminished Medium-Range Order Observed in Annealed Amorphous Germanium

We use variable coherence transmission electron microscopy to examine medium-range ordering in vacuum-deposited amorphous germanium. The method accesses higher-order atomic correlations through statistical analysis of hollow-cone dark-field image speckle. This yields greater sensitivity to medium-range order than the familiar pair correlation function obtained from diffraction. We find that thermal annealing of amorphous germanium reduces the degree of medium-range order, affirming the thermodynamic stability of the random network.