Abstract

Nanopatterning of solid surfaces by low-energy ion bombardment has received considerable interest in recent years. This interest was partially motivated by promising applications of nanopatterned substrates in the production of functional surfaces. Especially nanoscale ripple patterns on Si surfaces have attracted attention both from a fundamental and an application related point of view. This paper summarizes the theoretical basics of ion-induced pattern formation and compares the predictions of various continuum models to experimental observations with special emphasis on the morphology development of Si surfaces during sub-keV ion sputtering.

Highlights

  • Back in the 1960s, Navez et al studied the morphology of glass surfaces bombarded with a 4 keV ion beam of air [1]

  • Bradley and Harper developed a continuum model [29] to describe the formation of the ripple patterns based on the so-called micro-roughening instability [30]

  • Ghose [103] showed that the formation of a clearly developed rotated ripple pattern under 80◦ incidence can be induced at room temperature by a chemical pre-roughening of the Si surface which is known to influence the dynamics of the pattern development [45,91]

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Summary

Introduction

Back in the 1960s, Navez et al studied the morphology of glass surfaces bombarded with a 4 keV ion beam of air [1]. Several possible origins of the ripple patterns like ion-induced local stresses or initial surface defects have been suggested in the years following their discovery [3], no conclusive explanation could be found until 1988 In this year, Bradley and Harper developed a continuum model [29] to describe the formation of the ripple patterns based on the so-called micro-roughening instability [30]. The resulting linear continuum equation, the so-called Bradley-Harper (BH) equation, is able to reproduce some of the main experimentally observed features of the formation and early evolution of the patterns like their orientation with respect to the ion beam and the exponential growth of the ripple amplitude.

Continuum Theory of Ripple Formation During Low Energy Ion Sputtering
Sigmund’s theory of sputtering
The Bradley-Harper model
Kuramoto-Sivashinsky equation
Damped Kuramoto-Sivashinsky equation
General continuum equation
Coupled two-field model
Morphology of Ion-sputtered Si Surfaces
Evolution of the surface morphology
Formation of two ripple modes
Dynamic scaling behavior
Dynamics of topological pattern defects
Summary
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