Polarity-Induced Selective Area Epitaxy of GaN Nanowires.

We present a conceptually novel approach to achieve selective area epitaxy of GaN nanowires. The approach is based on the fact that these nanostructures do not form in plasma-assisted molecular beam epitaxy on structurally and chemically uniform cation-polar substrates. By in situ depositing and nitridating Si on a Ga-polar GaN film, we locally reverse the polarity to induce the selective area epitaxy of N-polar GaN nanowires.

GaAs-Fe₃Si core-shell nanowires: nanobar magnets.

Semiconductor-ferromagnet GaAs-Fe3Si core-shell nanowires were grown by molecular beam epitaxy and analyzed by scanning and transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetic force microscopy. We obtained closed and smooth Fe3Si shells with a crystalline structure that show ferromagnetic properties with magnetizations along the nanowire axis (perpendicular to the substrate). Such nanobar magnets are promising candidates to enable the fabrication of new forward-looking devices in the field of spintronics and magnetic recording.

Kinetic optimum of volmer-weber growth.

We find that the molecular beam epitaxy of Fe3Si on GaAs(001) observed by real-time x-ray diffraction begins by the abrupt formation of 3 monolayer (ML) high islands and approaches two-dimensional layer-by-layer growth at a thickness of 7 ML. A surface energy increase is confirmed by ab initio calculations and allows us to identify the growth as a strain-free Volmer-Weber transient. Kinetic Monte Carlo simulations incorporating this energy increase correctly reproduce the characteristic x-ray intensity oscillations found in the experiment.