EXTENDED-RANGE PROPAGATED ORDER IN AMORPHOUS SOLIDS

Atomic density fluctuations, extending to at least 35 angstrom, have been discovered in a large (13 824 atom) model of amorphous silicon (a-Si). This extended-range structural order has been found, in the case of a-Si, to arise from second-neighbour correlations preferentially propagating atomic-density fluctuations. The period of such low-amplitude, extended-range oscillations in atomic density, namely congruent-to 3.4 angstrom in the case of a-Si, is that associated with the position of the first sharp diffraction peak (FSDP), namely congruent-to 1.9 angstrom-1; indeed, the extended real-space fluctuations for r > 10 angstrom contribute almost as significantly to the intensity of the FSDP as do the much stronger, but less periodic, correlations in the range 0-10 angstrom.