Instability types at ion-assisted alloy deposition: from surface to bulk nanopatterning

Ion irradiation assistance of the film growth has a strong impact on structural properties. Here, we demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. Be means of linear stability analysis we show that the ion-to-atom arrival ratio is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion-induced surface roughness processes or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement coupling to the preferential sputtering or to the diffusivity are found to induce instabilities and pattern formation. Depending on the film growth and ion-irradiation conditions the instabilities show stationary or oscillating behavior. This presents opportunities to grow 3D laterally or vertically ordered nanostructures.