Self-organized Nanopatterns on Silicon Surfaces by Ion-Beam-Sputtering with Metal Co-deposition

The capability of ion beam sputtering (IBS) to induce surface nanopatterns on different materials (metals, semiconductors or insulators) is well-known since the early 60’s [1]. The first description of such phenomenology was proposed by Bradley and Harper (BH) [2] invoking the interplay between surface relaxation mechanisms and the sputtering yield dependence on the local surface curvature. BH model and posterior generalizations [1] predict pattern formation for any ion incidence angle and successfully account for the observation of nanoripple or nanodot structures depending on the irradiation geometry (anisotropic or isotropic, respectively). However, the universality of the BH approach has been recently questioned by the disparity of (sometimes conflicting) results. This ambiguous scenario has been partially clarified after the awareness of the role played by compositional modifications during IBS for both monoelemental [3] and binary [4] semiconductors and, specially, for nanodot pattern formation. In these studies, silicon has become a sort of model system due to its technological relevance but also from the mono-elemental nature as well as extreme flatness. Thus, IBS of silicon surfaces yields (ripple) pattern formation only above an incidence angle threshold (~45° for low-energy Ar+ [5]) unless (metal) impurities prone to react with the target (forming silicides) are inadvertently or intentionally added during the irradiation [6,7]. Despite the a-priori undesirable presence of impurities, IBS with simultaneous co-deposition has emerged as a novel method to tune and modify the pattern morphology and characteristics [6-10]. In addition, the morphological pattern is correlated with a compositional one, offering new potential applications. However, assessing such compositional variations at the nanoscale is not straightforward and demands of advanced characterization tools. In this talk, the present status of metal co-deposition during low- (< 10 keV) and medium-energy (10-200 keV) IBS of silicon surfaces will be presented, making special emphasis on the efforts to elucidate correlated morphological and compositional issues.

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