Linear stability and instability patterns in ion-sputtered silicon

Abstract

We study the patterns formed onAr+ ion-sputtered Si surfaces at room temperature as a function of the control parameters ionenergy and incidence angle. We observe the sensitivity of pattern formation to artifactssuch as surface contamination and report the procedures we developed to control them. Weidentify regions in control parameter space where holes, parallel mode ripples andperpendicular mode ripples form, and identify a region where the flat surface is stable. Inthe vicinity of the boundaries between the stable and pattern-forming regions, calledbifurcations, we follow the time dependence from exponential amplification tosaturation and examine the amplification rate and the wavelength in the exponentialamplification regime. The resulting power laws are consistent with the theory ofnonequilibrium pattern formation for a type I (constant wavelength) bifurcation at lowangles and for a type II (diverging wavelength) bifurcation at high angles. Wediscuss the failure of all sputter rippling models to adequately describe theseaspects of the simplest experimental system studied, consisting of an elemental,isotropic amorphous surface in the simplest evolution regime of linear stability.