Experimental, Theoretical and Numerical Studies of Ion-induced Self-organized Nanoripples on Solid Surfaces

Abstract

This thesis presents a theoretical and experimental study on the formation and growth of quasi-periodic ripple patterns on solid surfaces via Ion Beam-induced Self-Organisation (IBSO). Simulations use realistic material parameters and are compared with experimental data where applicable.

Ripple structures are formed on Si(111) and Ni surfaces by broad Ar⁺ ion beam irradiation at high incidence angles and room temperature. Atomic Force Microscopy reveals distinct surface behaviours: Ni shows stable wavelength and exponential amplitude (or interface width/surface roughness, w) growth, while Si exhibits wavelength coarsening and amplitude saturation. These trends are analyzed using the simplified Makeev-Cuerno-Barabási (spMCB) model, derived from the anisotropic Kuramoto-Sivashinsky framework. Differences in evolution are linked to a material and angle-dependent crossover time, τc , separating linear and nonlinear regimes.

To improve realism, the spMCB model is applied to initially rough surfaces. Ripple formation begins once a minimum interface width is reached. Greater initial roughness leads to higher amplitudes and shorter τc , in line with experimental trends. This provides insight into early-stage ripple development.

Though qualitatively consistent with experiments, the spMCB model shows quantitative differences. These are explored via Ni and Au experiments under identical conditions. Results suggest that ion-induced viscous flow in amorphous layers explains material-dependent behaviour. Estimated viscosities agree with previous studies, supporting this explanation.

Reintroducing propagation terms from the full MCB model affects nonlinear dynamics but not linear ones. The modified model accelerates the emergence of cancellation modes, producing rotated, coherent ripple structures at higher fluences.