Self-ordering of metallic surfaces in the trampoline structuring regime

Surfaces of some metals (copper and aluminum) and alloys (black and chromium–nickel stainless steels) were irradiated with argon ion-plasma flows under the trampoline mode conditions, i.e., at high ion current densities j≥10mAcm−2 and relatively low ion kinetic energies E=(50−200)eV, which brought about a formation of two-scale (micro-nano) hierarchical rough structures on the sample surfaces. In other experiments, black steel was preliminarily processed in the trampoline regime, and nano-clusters of stainless steel were deposited from an additional target mounted inside the same chamber. The deposited coatings reproduced the composition of the multi-component sputtered target. Strong adhesion between the coating and the sample was obtained, which was proved by dynamic micro-hardness measurements. A high quality of surface patterns created in the trampoline regime was ensured by the release of ion energy near the sample surface and the formation in the quasi-liquid state of a micro-nano-scale structure of the metal upper near-surface layers. Wettability measurements demonstrated that the freshly prepared textured surfaces were hydrophilic, whereas after tens-of-minutes exposures in the ambient atmosphere, they became hydrophobic. The dependence of the textures on the incidence angle θ was measured. It was shown that the increase of θ induces the expansion of micro-nano-scale formations on the surface. Theoretical calculations using the kinetic Monte Carlo approach and simulating the driving force of surface structuring (in our case, this is ion irradiation) were applied to analyze numerically the formation of hierarchical micro-nano-structures at the initial stage of surface modification when the seed inhomogeneities appear and evolve. The results qualitatively correlate with the experimental observations.