Increasing medium-range order in amorphous silicon with low-energy ion bombardment

We have observed the existence of medium–range order in amorphous silicon with the fluctuation electron microscopy technique. We hypothesize that this structure is produced during the highly nonequilibrium deposition process, during which nuclei are formed and subsequently buried. We test this hypothesis by altering the deposition kinetics during magnetron sputter deposition by bombarding the growth surface with a variable flux of low-energy (20 eV) Ar+ ions. We observe that medium–range order increases monotonically as the ion/neutral flux ratio increases. We suggest that this low-energy bombardment increases adspecie surface mobility or modifies local structural rearrangements, resulting in enhanced medium–range order via increases in the size, volume fraction, and/or internal order of the nuclei.