Y.C. Lan

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.

Low-temperature synthesis and photoluminescence of AlN

High-quality aluminum nitride powder was obtained through the reaction of aluminum metal with ammonia at 450 degrees C in an autoclave. The synthesized powder was characterized by X-ray powder diffraction, high-resolution transmission electron microscopy (HRTEM) and photoluminescence spectrum. X-ray diffraction and HRTEM indicated that the powder consisted of wurtzite AIN with an average size of about 32 nm. Photoluminescence spectrum confirmed the existence of a blue luminescence band in AIN due to nitrogen vacancies. A possible low-temperature synthesis mechanism was discussed

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

Structure and Heat Capacity of Wurtzite GaN from 113 to 1073 K

High pure wurtzite structure GaN has been synthesized by gas reaction method. Its structure was determined by powder x-ray diffraction using the Rietveld technique. The heat capacity C-p was measured from 113 to 1073 K, which can be represented by C-p = 0.362 + 3.010 x 10(-4)T - 3.411 x 10(3)T(-2) - 7.791 x 10(-8)T(2). NO measurable phase transition was observed in this temperature range.

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

Radial growth dynamics of nanowires

In this brief paper, wt: address the problem of the radial growth dynamics of a nanowire due to the vapor-solid (VS) process while at the same time it grows along its axial direction due to vapor-liquid-solid (VLS) process. We show that there exists a critical radius at a certain saturation and that the nanowire will thicken if its initial radius is larger than the critical radius and vice versa. Only when its initial radius is equal to the critical radius will the radius of the nanowire be uniform along its axial direction. In all other cases, the nanowire is tapered with a certain slope. The slope is relevant to the initial radius. The closer it is to the critical radius, the smaller is the slope and vice versa. Although the slope may be generally very small, it still does exist. This suggests that it is difficult to grow long nanowires with a uniform radius

Structure, magnetic susceptibility and resistivity properties of SrVO3

Abstract The crystallographic structure of the compound SrVO 3 has been determined by X-ray diffraction and refined by the Rietveld method. The structural analysis suggest SrVO 3 presents a cubic perovskite structure with a =3.8425(1) A, space group Pm3m , Z =1. The electrical resistivity measurement suggests metallic behavior for the oxide. Magnetic susceptibility measurement confirms that some trace impurities are still present in the nearly single phase specimen and affect the magnetic behavior of the samples.

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.

MORPHOLOGICAL STABILITY OF A NANOWIRE DURING GROWTH PROCESS

In this letter, we analyze the morphological stability of a nanowire during the vapor–solid (VS) side growth process at the same time as it grows along its axial direction by the vapor–liquid–solid (VLS) mechanism. The longitudinal perturbations due to the fluctuations of the growth conditions are introduced to describe the morphological variance of a nanowire along its fibre direction. It is shown that the side growth can induce the morphological instability for a nanowire with side perturbations if the perturbations wavelengths are larger than a nanowires perimeter.