Pure amorphous silicon (a-Si) is one of the most studied model systems for amorphous networks as it is well known that it undergoes relaxation upon thermal annealing to a new ‘state’, a state which might be the closest attainable to the perfect continuous random network.
Nanoindentation proved to be a powerful tool to distinguish between these different states of as-prepared and relaxed. For example, as-prepared ion-implanted a-Si will tend to deform via plastic flow under indentation, while relaxed ion-implanted a-Si will undergo a phase transformation to a metallic phase under pressure and further transformation to crystalline phases upon unloading. However, less is known about the mechanical and structural property correlations of other forms of a-Si, pure and deposited, and this study addresses these issues.
Other forms of a-Si have been studied using nanoindentation, Raman microspectroscopy and fluctuation electron microscopy. The first form discussed here is the so-called pressure-induced a-Si, a pure form of a-Si created itself by indentation of crystalline silicon. This pressure-induced a-Si undergoes relaxation in the same manner as ion-implanted a-Si does, resulting in the same phase transformation behaviour and also same short-range order. Interestingly, the medium-range order of the two as-prepared forms, ion-implanted and pressure-induced, proved to be very different reflecting clearly the different formation processes.
Additionally, forms of a-Si created by deposition methods have been studied. The influence of a relaxation anneal on such a deposited forms of a-Si will be compared to the formation of an almost perfect continuous random network upon annealing as exhibited by pure forms of a-Si. |