Substantial Crystalline Topology in Amorphous Silicon

Using electron correlograph analysis we show that coherent nanodiffraction patterns from sputtered amorphous silicon indicate that there is more local crystallinity in unannealed amorphous silicon than was previously suspected. By comparing with simulations for various models we show that within a typical unannealed amorphous silicon film a substantial volume fraction (>50%) is topologically crystalline with correlation lengths up to 2 nm. Electron correlograph analysis is a variant of the fluctuation electron microscopy technique and its sensitivity to local crystalline ordering is derived from its sensitivity to four-body correlations.