Surface Patterning of Ge and Si by Heavy Ion and Cluster Impacts: Experiments, Atomistic Simulations and Theory

The driving forces for pattern formation on surfaces by ion irradiation have been under discussion for many years. Bradley and Harper published a straightforward derivation of a partial differential equation based on the surface curvature dependent sputtering, which describes some features. Later on, ion impact induced viscous flow and a mass drift in the amorphous surfaces layer caused by the impinging ions where discussed. Only a few years ago it became obvious that on semiconductor surfaces the formation of many of the beautiful patterns are dominated by contaminations with metals. Thus, a discussion started, whether the pattern formation is induced by preferential sputtering of one of the components or by driving forces like phase separation. Additionally, the kinetics of the collision-induced defects in a sub-surfaces layer can produce instabilities resulting in surface pattern. In order to identify the dominating driving forces at least for Ge and Si surface patterning by heavy ion (Bi) and cluster (Bi3) impacts of a few to a few tens of keV, experimental Focussed Ion Beam (FIB) and broad-beam studies were combined with computer experiments (MD and kinetic Monte Carlo simulations) and theoretical studies, e.g. of the damped Kuramoto-Sivashinsky equation. A detailed comparison between experiments, simulations and PDE solutions of the surfaces evolution of specificmorphologies is a powerful approach for a deeper understanding of this kind of self-organization of structures. In this abstract for each approach, experiment, simulation and theory, an example is presented. Experiments cover a wide range of ion energies and fluences. The atomistic simulations study the influence of the ion collision cascades on the pattern formation via defect kinetics. And finally, relations of this defect kinetics to parameters of the damped Kuramoto-Sivashinsky equation are studied.