X.L Chen

Formation of GaN nanorods by a sublimation method

Abstract GaN nanorods with diameters of 10–45xa0nm were formed through a simple sublimation method. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). SEM images showed that the nanorods were straight. XRD, SAED and HRTEM indicated that the nanorods were wurtzite GaN single crystals.

Blue emission and Raman scattering spectrum from AlN nanocrystalline powders

Photoluminescence and Raman scattering spectra from AIN nanocrystalline powders are studied. A blue emission band centered at 420 nm (2.95 eV) is observed. This band may be ascribed to the transition from the shallow level of V-N to the ground state of the deep level of the V-Al(3-)-3 x O-N(+) defect complexes. A phonon structure resulting fi om the transition from the shallow level to the excited states of the deep level is also observed. The broadening of peaks and the low-wave-number-shift of the phonon frequency observed on the Raman scattering spectra are the result of nano-sized effects

Syntheses and structure of nanocrystalline gallium nitride obtained from ammonothermal method using lithium metal as mineralizator

A double layer CeO2/Nb2O5 thin film by magnetron sputtering was prepared. The property and microstructure of the thin film were carefully characterized by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and high resolution transmission electron microscopy, XPS measurement clearly demonstrated that the Nb2O5 layer underlying CeO2 as a electrical-conductive layer could greatly improve the reduction ability of CeO2 thin film compared with that of a single layer CeO2 thin film: Fitting to the XPS experimental data and deconvoluting the spectra showed the increase of Ce3+ concentration in the double layer CeO2/Nb2O5 thin film. The microstructure of the double layer thin film was composed of three distinguishable layers, which are a polycrystalline CeO2 layer, an amorphous Nb2O5 layer, and an intermediate amorphous layer with regard to the silicon substrate. The interface between CeO2 and Nb2O5 was rough and indistinct. A detailed analysis was given from the viewpoint of interdiffusion at the CeO2/Nb2O5 interface

Synthesis and structure of nanocrystal-assembled bulk GaN

A new condensed form of GaN, nanocrystal-assembled bulk (NAB) GaN, was obtained directly from reactions of metal Ga and NH4Cl in liquid ammonia at 350-500 degrees C. High-resolution transmission electron microscopy observations reveal that the NAB GaN consists of well-crystallized nanocrystals with wurtzite structure. The synchronous densificated NAB GaN is transparent to visible light while the constituted nanocrystals have an average size of about 12 nm. A possible synthesis mechanism is discussed

Observation of a quantum-confinement effect with GaN nanoparticles synthesized through a new gas reaction route

Abstract.Spherical wurtzite GaN nanoparticles with diameters of 5–8xa0nm were synthesized through a new gas reaction route. The concave-surface-induced nucleation process based on the surface roughness of the substrate played an important role in the formation of quantum dots. Photoluminescence spectrum revealed the quantum-confined excited states in the nanoparticles with features at 3.73xa0eV (332xa0nm) and 3.85xa0eV (322xa0nm), which show significant blueshift compared with the band-gap emission from bulk GaN crystals. Four blue emission bands with low intensity, centered at 2.85xa0eV (435xa0nm), 2.75xa0eV (451xa0nm), 2.67xa0eV (464xa0nm), 2.62xa0eV (473xa0nm) respectively, were also observed. These blue bands may originate from surface states.

Synthesis, Raman scattering, and infrared spectra of a new condensed form of GaN nanophase material

A new form of transparent condensed nanophase material of GaN was synthesized directly by ammono-thermal synthetic route. Nano-sized effects and thermal stability of that material were investigated through Raman scattering and infrared spectra. Compared with bulk GaN, we observed the Raman low-energy-shift of the phonon frequency of E-2(high) and the transverse optical mode [E-1(TO)], the infrared high-energy-shift of omega(T), and the variation of relative intensity I-E2/E1(TO). These characteristics can be attributed to the existence Of the interface effects and the vacancy of N in the GaN nanophase material. This material has a high thermal stability even at 900 degrees C as indicated through infrared and Raman spectral investigation of annealed samples of as-synthesized nanophase material.

Structure and superconducting properties of chemically oxidized La2CuO4+y under hydrothermal conditions

Stoichiometric La2CuO4 was chemically oxidized under hydrothermal conditions in KMnO4 solutions above 100 degrees C. The structure and superconducting properties of the oxidized La2CuO4+y were studied by X-ray powder diffraction and magnetic susceptibility measurements. A large orthorhombic distortion was observed for the oxidized samples from X-ray diffraction. The oxidized La2CuO4+y shows a high superconducting transition up to 42 K. Chemical oxidation under hydrothermal conditions is effective in inserting oxygen into La2CuO4 because of equilibrium and of higher oxidation temperatures

Fabrication of nano-sized AlGaN alloy by dry milling and thermal annealing

Al0.61Ga0.39N alloy nano-powders were obtained by a thermal annealing process from the Al+GaN system in NH3 flow. The activation process of nano-sized Al and GaN powders during dry milling in N-2 plays a key role in the formation of the AlGaN alloy. A too high fraction of aluminium leads to AM, while a too low fraction results in insufficient activation of the Al powder. The GaN localized mode and the AIN localized mode of the E-2 phonon frequency, and the one-mode-type behavior of the A,(LO) and A,(TO) phonon frequencies were observed in the Raman spectra of the alloy

Morphology of GaN in ammonia

chinese acad sci, inst phys, beijing 100080, peoples r china. chinese acad sci, ctr condensed matter phys, beijing 100080, peoples r china. acad sinica, int ctr mat phys, shenyang 110015, peoples r china.;lan, yc (reprint author), chinese acad sci, inst phys, pob 603, beijing 100080, peoples r china