# Pattern Formation on Alloys by Cluster Ion Beam Irradiation
###### Abstract  
Surface nanopatterning induced by ion beam irradiation allows for the creation of patterns on large areas of a wide variety of materials. However, surface composition plays a crucial role in the process. In this study, we investigate the bombardment of a metallic alloy, specifically an Au-Cu system with different compositions, discussing differences in the formation of patterns compared to pure materials. Mixtures with compositions ranging from 35 to 65 at.% Cu exhibit a dampening effect on ripple height and depth. At intermediate angles of incidence, horizontal displacement is minimized and sputtering maximized; conversely, at grazing angles, sputtering is minimized and horizontal displacement becomes dependent on material mobility. It is, therefore, evident that sputtering determines the patterning for intermediate angles. However, an analysis of the redistribution factor as a function of the angle of incidence shows that the weight of the redistribution is much lower than that of sputtering in alloys of similar composition at grazing angles due to the amorphization process. This point is confirmed by the data on displaced atoms obtained from the relocation cross-sections. s +
Footnote †: journal: Applied sciences  
0000-0001-5000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-0000-00000-00000-00000-00000-00000-00000-000  
flow, stress effects, ion implantation, etc.) [11; 12; 13], a complete understanding of the surface patterning induced by ion beam irradiation has not been achieved. The main conclusion from the experimental findings is that patterning is not a universal process but depends on the ion/target combination [2]. In fact, we have not found in the recent literature any experimental work addressing this issue on the materials analyzed in this work. The first attempt to model a binary compound was made by [PERSON] et al. [14]. These authors obtained surface compositional variations. Later, [PERSON] and [PERSON] [15] developed a two-field model to explain pattern formation in compound materials, patterns such as those obtained experimentally by [PERSON] et al. [16] on GaSb. In their lastest study on the subject [17], they introduced into the previous model an ion-induced diffusion current term similar to that introduced by [PERSON] et al. [7]. Recently, it has become possible to directly observe the formation of patterns using MD on amorphous silicon surfaces under very low incident energies of 30 eV [18; 19]. In previous works [20; 21], we studied pattern formation in pure metallic systems and concluded that, at intermediate angles, the process is primarily governed by redistribution, while at grazing angles, it is dominated by sputtering. When the surface consists of different atomic species, local differences emerge in processes such as sputtering and surface displacement due to the distinct components, which, in turn, influence pattern formation. These effects could even induce phase separations within surface patterns [2]. Furthermore, the surface morphology could be altered depending on the composition. Not all particles in the solid have the same mobility or the same erosion tendency. In summary, this work addresses two objectives. On the one hand, the current literature does not clarify what processes lead to the formation of surface patterns in alloys; on the other, the structural and morphological differences between alloy patterns and patterns in pure metals are unclear. In the case of metals, the crystalline structure remains intact during the process. The diffusive regime, which depends on crystal symmetry, plays a secondary role compared to the erosive regime under conditions of high ion fluence and/or low surface temperature [22]. In this way, the results are determined by the erosive phase. In this work, we investigate the influence of both processes, namely sputtering and redistribution, on the formation of surface patterns during cluster bombardment of Au-Cu alloys.