Ion-beam nanopatterning of silicon surfaces under co-deposition of non-silicide-forming impurities

TL;DR

This study demonstrates that silicon surfaces can form nanopatterns under ion-beam irradiation with gold impurities, even without silicide formation, challenging existing models that require silicide formation for patterning.

Contribution

It shows nanopatterning occurs with non-silicide-forming impurities, providing detailed chemical and morphological analysis and discussing implications for current models.

Findings

Ripples with nanometric wavelengths form despite Au not forming stable silicides.

Surface composition and amorphization dynamics influence pattern formation.

Pattern orientation varies with distance to Au source.

Abstract

We report experiments on surface nanopatterning of Si targets which are irradiated with 2 keV Ar + ions impinging at near-glancing incidence, under concurrent co-deposition of Au impurities simultaneously extracted from a gold target by the same ion beam. Previous recent experiments by a number of groups suggest that silicide formation is a prerequisite for pattern formation in the presence of metallic impurities. In spite of the fact that Au is known not to form stable compounds with the Si atoms, ripples nonetheless emerge in our experiments with nanometric wavelengths and small amplitudes, and with an orientation that changes with distance to the Au source. We provide results of sample analysis through Auger electron and energy-dispersive X-ray spectroscopies for their space-resolved chemical composition, and through atomic force, scanning transmission electron, and high-resolution transmission microscopies for their morphological properties. We discuss these findings in the light of current continuum models for this class of systems. The composition of and the dynamics within the near-surface amorphized layer that ensues is expected to play a relevant role to account for the unexpected formation of these surface structures.