Observations of structural order in ion-implanted amorphous silicon

Abstract

Medium-range order in ion-implanted amorphous silicon has been observed using fluctuation electron microscopy. In fluctuation electron microscopy, variance of dark-field image intensity contains the information of high-order atomic correlations, primarily in medium-range order length scale (1–3 nm). Thermal annealing greatly reduces the order and leaves a random network. It appears that the free energy change previously observed on relaxation may therefore be associated with randomization of the network. In this paper, we discuss the origin of the medium-range order during implantation, which can be interpreted as a paracrystalline state, that is, a disordered network enclosing compacts of highly topologically ordered grains on the length scale of 1–3 nm with significant strain fields.

Disentangling Neighbors and Extended Range Density Oscillations in Monatomic Amorphous Semiconductors

“…Paracrystalline models do indeed depict more dihedral order than CRN models; however, the FEM shows that the order decreases with annealing [14] whereas here we clearly observe an increase.…”

Phase transformations induced by spherical indentation in ion-implanted amorphous silicon

“…[11][12][13] An early high-pressure ͑diamond anvil͒ study on vacuum-evaporated a-Si reported a transformation to a metallic phase that was consistent with high density amorphous Si. We believe that the mechanical behavior can be explained by well documented structural differences [19][20][21][22] between highly defective or paracrystalline unrelaxed a-Si and the fully fourfold coordination of relaxed a-Si which has only short range order and is a continuous random network ͑CRN͒. A further study based on diamond anvil results has also proposed that a-Si should undergo a transformation to a high density ͑metallic͒ amorphous phase during loading and transform back to its original low density a-Si state during unloading.…”

Electron Irradiation on Amorphous Silicon

“…If the structure changes dramatically during image acquisition, we will not be able to reproduce the results. In previous work [5,9], as-prepared and near-surface amorphous silicon is found to be paracrystalline. Is this paracrystalline structure beam-sensitive and how will it change with electron energy?…”

“…Indeed, this prediction is confirmed by our experiments, which were done separately in the JEOL 4000 and Philips CM12 microscopes (we ever attempted to use one microscope to do both hollow cone and dark field, but did not succeed). The operating conditions for these microscopes can be found elsewhere [5,6].…”