Wavelength Tunability of Ion-bombardment Induced Ripples on Sapphire

TL;DR

This paper investigates how the wavelength of ion-bombardment induced ripples on sapphire surfaces can be widely tuned by adjusting the ion incidence angle, revealing different relaxation mechanisms at play.

Contribution

It demonstrates the wavelength tunability over nearly two orders of magnitude on sapphire surfaces and analyzes the underlying relaxation mechanisms involved.

Findings

Wavelength varies over two orders of magnitude with ion incidence angle.

Viscous flow explains ripple formation at low temperature and large angles.

Surface diffusion may dominate at high temperature.

Abstract

A study of ripple formation on sapphire surfaces by 300-2000 eV Ar+ ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range-nearly two orders of magnitude-by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30. In this model, relaxation is confined to a few-nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation.