Measurement of Ehrlich-Schwoebel barrier contribution to the self-organized formation of ordered surface patterns on Ge(001)

TL;DR

This study investigates how the Ehrlich-Schwoebel barrier influences the self-organized nanoscale pattern formation on Ge(001) surfaces during ion bombardment, using real-time GISAXS measurements to compare smoothing and patterning processes.

Contribution

It provides the first quantitative estimation of the Ehrlich-Schwoebel barrier's role in nanoscale pattern formation on crystalline Ge surfaces.

Findings

Ehrlich-Schwoebel barrier contributes significantly to pattern formation.

Linear theory accurately describes early-stage surface kinetics.

Comparison quantifies the barrier's impact on surface instability.

Abstract

Normal incidence 1 keV Ar$^+$ ion bombardment leads to amorphization and ultrasmoothing of Ge at room temperature, but at elevated temperatures the Ge surface remains crystalline and is unstable to the formation of self-organized nanoscale patterns of ordered pyramid-shaped pits. The physical phenomenon distinguishing the high temperature patterning from room temperature ultrasmoothing is believed to be a surface instability due to the Ehrlich-Schwoebel barrier for diffusing vacancies and adatoms, which is not present on the amorphous material. This real-time GISAXS study compares smoothing of a pre-patterned Ge sample at room temperature with patterning of an initially flat Ge sample at an elevated temperature. In both experiments, when the nanoscale structures are relatively small in height, the average kinetics can be explained by a linear theory. The linear theory coefficients, indicating surface stability or instability, were extracted for both experiments. A comparison between the two measurements allows estimation of the contribution of the Ehrlich-Schwoebel barrier to the self-organized formation of ordered nanoscale patterns on crystalline Ge surfaces.