New Precursor Routes to Nanocrystalline Cubic/Hexagonal Gallium Nitride, GaN

ABSTRACTTwo precursor routes culminating in bulk nanocrystalline gallium nitride materials are reported, with emphasis on the materials' XRD/crystalline features and photoluminescence (PL). First, the new polymeric gallium imide, {Ga(NH)3/2}n, can be converted to nanocrystalline, cubic/hexagonal GaN ranging in color from yellow to light gray. Second, a new route to gallazane, [H2GaNH2]x, from the combination of LiGaH4 and NH4X (X = Cl, Br) in Et2O is shown to result in a material that slowly converts to a polymeric solid via H2 and NH3 elimination-condensation pathways. Both the gallazane and the polymeric solid are pyrolyzed to dark gray nanocrystalline, phase-inhomogeneous GaN as above. Specific variations in the pyrolysis conditions enable some control over the particle nanosize and a degree of crystalline phase-inhomogeneity of the materials. These nanophase GaN materials have also been characterized by room temperature photoluminescence (PL) measurements. In general, the observed emission spectra are strongly dependent on pyrolysis temperature and typically exhibit weak defect yellow-green emission. While the as-prepared GaN does not exhibit band-edge PL, a brief hydrofluoric acid etch yields nanophase GaN exhibiting an intense blue-emitting PL spectrum with an emission maximum near 420 nm.</jats:p

An Overview of Rock Avalanche-Substrate Interactions

Large rock or debris avalanches inevitably encounter and interact with a variety of earth materials along their paths. These substrate materials influence rock and debris avalanche emplacement in one or several of the following ways (1) longer runout due to an increase in volume by entrainment on the steep failure slope, (2) higher mobility by reduction in basal frictional resistance (e.g. emplacement over glacier ice), or (3) a larger area of deposition due to transformation into debris flows, contrasted by (4) runout impediment due to interactions along the flatter runout path (e.g. bulldozing of substrate material or entrainment of high-friction debris), and introducing (5) flow complexities resulting from changes in basal mechanical properties and other localized interactions. Additionally, the total area affected by a rock avalanche may extend beyond the deposit margin itself when sediments in front of the rock avalanche are bulldozed or are mobilized and flow independent of the rock avalanche for some further distance