Normal incidence ion irradiation at elevated temperatures, when amorphization is prevented, induces novel nanoscale patterns of crystalline structures on elemental semiconductors by a reverse epitaxial growth mechanism: on Ge surfaces irradiation at temperatures above the recrystallization temperature of 250{\deg}C leads to self-organized patterns of inverse pyramids. Checkerboard patterns with fourfold symmetry evolve on the Ge (100) surface, whereas on the Ge (111) surface, isotropic patterns with a sixfold symmetry emerge. After high fluence irradiations these patterns exhibit well developed facets. A deterministic nonlinear continuum equation accounting for the effective surface currents due to an Ehrlich-Schwoebel barrier for diffusing vacancies reproduces remarkably well our experimental observations.
@article{arxiv.1303.5133,
title = {Reverse epitaxy of Ge: ordered and facetted surface patterns},
author = {Xin Ou and Adrian Keller and Manfred Helm and Jürgen Fassbender and Stefan Facsko},
journal= {arXiv preprint arXiv:1303.5133},
year = {2015}
}