Microscopic description of the surface dipole plasmon in large Na_N clusters (950 < N < 12050)

Fully microscopic RPA/LDA calculations of the dipole plasmon for very large neutral and charged sodium clusters, Na_N^Z+, in the size range 950 < N < 12050 are presented for the first time. 60 different sizes are considered altogether, which allows for an in-depth investigation of the asymptotic behavior of both the width and the position of the plasmon.Comment: Latex/Revtex, 4 pages with 4 Postscript figures, accepted for publication in Physical Review

Ga-polar GaN nanocolumn arrays with semipolar faceted tips

Selective area growth of GaN nanocolumns (NCs) by molecular beam epitaxy on laser ablated pre-patterned GaN(0001) templates is shown to provide regular arrays of Ga-polar NCs. The Ga diffusion-assisted growth mechanism is analyzed and the experiments suggest that the effective growth conditions vary with the height of the NCs due to Ga diffusion on the mask and the NC sidewalls, ranging from N-rich up to stoichiometry. The obtained morphology with semipolar facets at the tip is discussed within the framework of equilibrium thermodynamics, which provides a consistent picture also for the growth of N-polar NCs with flat tips. The structural investigation reveals almost defect-free semipolar $\{1\overline {1}02\}$ GaN facets at the top of the NCs, which is known to be a promising way of producing templates for nanoscale semipolar GaN-based heterostructures. Almost no polarization discontinuity is expected for InxGa1−xN/GaN interfaces on such facets.Open-Access-Publikationsfonds 2013peerReviewe