Observations of structural order in ion-implanted amorphous silicon

Medium-range order in ion-implanted amorphous silicon has been observed usi ng fluctuation electron microscopy. In fluctuation electron microscopy, var iance 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. I t 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 networ k enclosing compacts of highly topologically ordered grains on the length s cale of 1-3 nm with significant strain fields.