We present a new approach to achieve selective area growth of GaN nanowires by plasma-assisted molecular beam epitaxy. The nanowires are grown on graphene nanodots, which are patterned by electron beam lithography from polycrystalline graphene patches transferred to SiO2 substrates. The GaN nanowires grow on these graphene nanodomains with a perfect selectivity with respect to the SiO2 surrounding surface. The results demonstrate that a single monolayer of graphene can withstand the lithography process without losing its ability to induce epitaxial growth. The nanowire length distribution and patterns’ fill factor are analyzed in the framework of a theoretical model, which takes into account an incubation time dependent on the graphene dot size. Overall, these results represent the first demonstration of selective area nanowire growth on a regular array of graphene nanodomains.

Topological insulator spin-polarized surface states are attractive for spintronic applications, in particular for spin-charge current interconversion, where extremely high conversion efficiencies are predicted. However, the contribution of topologically trivial bulk states is often disregarded although it may play a crucial role in the experimental results and extracted conversion efficiencies. The presence of bulk states at the Fermi level can be avoided by increasing the gap using the confinement effect appearing as the film thickness is reduced. We address this topic by growing Bi 1−x Sb x thin films (2.5-15 nm) by molecular beam epitaxy on InSb, BaF 2 , and Si substrates. The surface electronic band structure is studied by angle-resolved photoemission spectroscopy. Two Bi 1−x Sb x surface states are observed in the gap for several Sb concentrations and thicknesses, across the topological insulator phase, scanning x between 7% and 30%. Tight-binding calculations of the surface states are in good agreement with the experiments, revealing their polarized nature. Surface states are still present at the point for the thinnest films (2.5 nm), suggesting highly confined polarized states at the surface.