Situ Growth Of Gan, Geo <sub> 2 </ Sub> One-dimensional Nanostructures And Luminescence Properties

Nanobelts and zigzag-shaped nanowires of GaN and nanowires and pattemed microwires of GeO₂ have been in-situ grown on the surface of gallium grains and germanium wafers on a large scale,respectively.The morphologies,crystal structures and photoluminescence properties of the 1 dimensional(1 D) GaN and GeO2 nanostructures were investigated,and the possible growth mechanisms were also proposed to account for the formation of GaN and GeO2 nanostructures with different morphologies.These investigative results would provide a base for research of photoelectric properties and application of 1 D GaN and GeO₂ nanostructures.(1) Nanobelts,nanorings and zigzag nanowires of GaN have been in-situ grown on the surface of gallium grains by heating metallic gallium under the flow of H₂ and NH₃ for 30 minutes(The tube was not evacuated by a vacuum pump before introduction of H₂ and NH₃ gases).The as-synthesized products of GaN are all single crystalline phase with the hexagonal structure.The GaN nanobelts have widths in the range of 20 to 300 nm and lengths of up to 30μm.The diameters of the nanorings and zigzag nanowires are 5-8μm and 160 nm,respectively.The influences of the reaction temperature and time on the products development were experimentally investigated,and a possible mechanism was also proposed to account for the formation of GaN nanostructures with different morphologies.The GaN nanostructures exhibited a strong UV emission with peak at 361 nm and a weak blue emission with peak at 456 nm.The UV and blue emissions are assigned to the free exciton emission from the wide band gap of GaN and transition from a shallow donor to deep localized acceptor,respectively.(2) Nanowires,zigzag-shaped nanowires and nanosaws of GaN have been in-situ grown on the surface of gallium grains and Al₂O₃ substrates by reaction of metallic gallium with NH₃(The corundum tube was pumped to remove residue air before introduction of H₂ and NH₃ gases.).The as-synthesized GaN nanostructures with different morphologies are all single crystalline phase with the hexagonal structure.The GaN nanowires have diameters in the range of 90 to 650 nm and lengths of up to 30μm.The zigzag-shaped GaN nanowires have uniform diameters,with an average diameter of about 300 nm and length up to 150μm.The growth of GaN nanostructures is under the control of the Vapor-Solid mechanism.The formation of GaN nanostructures with different morphologies was explained.The GaN nanostructures exhibited a strong UV emission with peak at 362 nm and a weak blue emission with peak at 460 nm.The UV and blue emissions are assigned to the free exciton emission from the wide band gap of GaN and transition from a shallow donor to deep localized acceptor,respectively. (3) GeO₂ nanowires have been in-situ grown on the surface of germanium wafers on a large scale by heating germanium wafers coated with an Au film at 450-700℃under the flow of H₂O. The GeO₂ nanowires synthesized at 450-500 and 600-700℃are single crystalline phase with the cubic and hexagonal structure,respectively.The diameters and the lengths of GeO₂ nanowires was controlled in the range of 20-150 nm and 500 nm-200μm by varying the heating temperature and time.The growth of GeO₂ nanowires is under the control of the Vapor-Liquid-Solid mechanism.A strong UV emission with peak at 352 nm and two blue emissions with peaks at 397 and 480 nm were observed in the GeO₂ nanowires.The UV and blue emissions may be assigned to transition between the oxygen vacancy and interstitial oxygen and radiative recombination between an electron on an oxtygen vacancy and a hole on an germanium-oxygen vacancy center in the GeO₂ nanowires, respectively.(4) The patterned square of Au catalysts was prepared on the surface of germanium substrate by the UV photolithography technology.The patterned GeO₂ microwires have been in-situ grown on the surface of the germanium wafer with pattemed Au catalysts at 600℃in an air atmosphere.The as-synthesized GeO₂ microwires have a hexagonal structure with diameter of 1μm and length up to 10μm.A possible mechanism of Solid-Liquid-Solid for germanium and Vapor-Liquid-Solid for oxygen was proposed to account for the growth GeO₂ microwires.