Paper NS-TuP11
Clarifying the Role of Surface Chemistry in Fabrication of Large Nanostructured Surfaces using Ion Irradiation

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

Formation of hexagonally ordered nanodots on GaSb surfaces during ion sputtering in the late 1990s has invigorated interest in using low energy ion irradiation for nanostructuring and functionalization of material s surfaces. However, the underlying physical phenomena behind this technique remain poorly understood, leaving many questions about the mechanisms of nanostructure formation via ion irradiation unanswered. This dearth of understanding stems in part from the fact that research in this area has focused thus far primarily on surface structure, and not surface chemical composition. A surge of interest toward the role chemical processes play in forming morphology of surfaces irradiated by ion beams is evidenced by a series of recent works on surfactant sputtering and silicide induced ion beam patterning. In view of this growing interest, we report herewith experimental results on surface nanostructuring of Si via irradiation by low energy inert gas ions in various arrangements featuring co-deposition of impurity atoms on irradiated surfaces in order to “seed” the formation of nanostructures. These atoms were sputtered from smaller targets of various geometries placed close to Si samples. Such arrangements allow for controllable variation of the fluence, impact energy, and incidence angle of bombarding ions as well as of the surface concentration of impurity atoms. Instead of focusing on previously well studied fine nanoripple and nanodot patterns, this work concentrates on courser surface morphologies obtained at fluences nearing 10¹⁹ ions/cm². These ion-irradiated nanostructured samples have been comprehensively characterized by structure-sensitive (SEM, AFM and XRD) and composition-sensitive (XPS and TXRF) experimental techniques in order to better understand the interplay between chemical composition and structure of their surfaces. It has been confirmed that the nanostructured surfaces were much easier obtainable via the “seeding” approach. Moreover, using Si as the “seeding” target failed, in contrast to Cu and stainless steel targets that helped produce feather-like arrays of tilted amorphous nanopillars/nanocones homogeneously covering large surface areas exceeding 100 mm². This necessity of using certain metal surfactants for nanostructure formation proved the importance of surface chemistry in formation of the surface structure under ion irradiation. Experimental results on surface processing with low energy ion beams and compositional-versus-structural characterization obtained in this work will be discussed and interpreted in our presentation at the Meeting.