Reverse epitaxy of Ge: ordered and facetted surface patterns

TL;DR

This study investigates how high-temperature ion irradiation induces self-organized, facetted nanoscale patterns on germanium surfaces through a reverse epitaxial growth mechanism, revealing symmetry-dependent pattern formation.

Contribution

It introduces a novel understanding of pattern formation on Ge surfaces via ion irradiation and develops a deterministic nonlinear continuum model to explain the observed phenomena.

Findings

Checkerboard patterns with fourfold symmetry on Ge(100)

Sixfold symmetric patterns on Ge(111)

Facetted patterns at high fluence irradiation

Abstract

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.