Relative free energies of Si surfaces

Cavities are formed by ion implanting (001) Si with He and annealing at 800 °C to enlarge and to remove the He. Subsequent annealing at 600 °C results in cavities with well-defined facets as seen in [110] cross section with transmission electron microscopy. The most frequently observed facets are {111} planes. A rounded surface is seen about the [001] direction of all cavities, and (11̄0) facets are seen less frequently. The cavities allow the equilibrium crystal shape of Si to be examined and the relative free energies of the observed planes to be measured. The surface free energies of {001} and {110} planes are found to be 1.09±0.07 and 1.07±0.03 times that of {111} planes, respectively.