[en] (Ti,Al)N films were deposited by an off-plane double bend filtered cathodic vacuum arc technique in N₂ ambient at room temperature. X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the film structure. The influence of deposition pressure and the substrate bias on the XRD patterns and Raman spectra were systematically studied. As deposition pressure is increased, the film structure evolves from metallic, to metal rich (Ti,Al)₂N, and finally to a single face-centered cubic (Ti,Al)N. As substrate bias is increased, the structure evolves from amorphous to crystalline (Ti,Al)N for bias at 200 V. Further increase of substrate bias results in the decrease of the crystalline size and increase of disorder phase. Four peaks at 238, 326, 442, and 679 cm-1, arisen from the transverse acoustic, longitudinal acoustic, transverse acoustic optical, and longitudinal acoustic modes of (Ti,Al)N phase, respectively, can be observed in the Raman spectra. The variation of the Raman spectra with the deposition pressure and substrate bias are in good agreement with that of the XRD measurements. [copyright] 2001 American Institute of Physics

[en] Zirconium oxide thin films were grown on n-Si(100) and quartz substrates by using an off-plane filtered cathodic vacuum arc without external heating. A Zr cathode was used to obtain the plasma and the deposition rate was varied from 75 to 35 nm min^-1 corresponding to various oxygen flow rates. Optical properties of as-deposited films are presented as a function of oxygen flow rate and shown to depend greatly on it. The transmittance and optical band gap (E_g) increase with the oxygen flow rate whereas optical constants decrease. Film optical homogeneity is considerably enhanced and good homogeneity is exhibited for the films deposited at oxygen flow rate above 50 sccm. Structural homogeneity remains throughout the film depth even though the respective film structure changes with the different oxygen flow rates. Bulk-like stoichiometric amorphous zirconium oxide film exhibits high E_g (5.0 eV), high transmittance and good optical constants (high refractive index of 2.16 at 550 nm and low extinction coefficient of ∼ 10^-5 at 550 nm) with homogeneous structure

[en] Iron containing diamond-like amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe content and substrate bias on the surface energy of the films were investigated. The surface energy of a-C:Fe films was determined by the contact angle measurement. Atomic force microscopy, Raman spectroscopy, and x-ray induced photoelectron spectroscopy were employed to analyze the origin of the variation of surface energy with various Fe content and substrate bias. It is found that the contact angle for water increases significantly after incorporating Fe into the films and the films become hydrophobic. The roughness of these films has no effect on the contact angle. The surface energy is reduced from 42.8 to 25 dyne/cm after incorporating Fe into the a-C film (10% Fe in the target), which is due to the reduction of both dispersive and polar component. The reduction in dispersive component is ascribed to the decrease of atomic density of the a-C:Fe films due to the increase in sp² bonded carbon. When sp² content increases to some extent, the atomic density remains constant and hence dispersive component does not change. The absorption of oxygen on the surface plays an important role in the reduction of the polar component for the a-C:Fe films. It is proposed that such network as (C_n - O - Fe) - O - (Fe - O - C_n) may be formed and responsible for the reduction of polar component. [copyright] 2001 American Institute of Physics

[en] Aluminium nitride (AlN) films have been fabricated on Si(100) substrates by an ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The structural and mechanical properties of the AlN films have been investigated using x-ray photoelectron spectroscopy, by means of an x-ray diffractometer, visible Raman spectroscopy, atomic force microscopy and nanoindentation. The AlN films exhibit a predominant a-axis orientation with hardness as high as 14.5 GPa, which may be suitable for surface acoustic wave devices

[en] We report on the successful fabrication of transparent and uniform aluminium nitride (AlN) III-V semiconductor films using an ion-beam assisted filtered cathodic vacuum arc technique at room temperature. A nitrogen-ion beam with energy varying from 200 to 650 eV has been employed to assist the deposition of AlN films. Effects of the nitrogen-ion-beam energy on optical and structural properties of AlN films have been investigated using an optical spectrophotometer, visible Raman spectroscopy, x-ray diffraction, atomic force microscopy and nanomechanical test instruments. The optical and structural properties of the AlN films depend significantly on the nitrogen-ion-beam energy. The AlN films deposited under ion energies below 300 eV are all amorphous and enhanced polycrystalline AlN films are obtained for energies above 400 eV

[en] A facile catalysis-free method has been utilized to synthesize functional samarium hexaboride (SmB₆) nanowires. Structural characterization shows that the nanowires are single-crystalline SmB₆ with the [1 0 0] growth direction. These nanowires exhibit a low turn-on electric field of 4.2 V μm^-1 based on the 10 μA cm^-2 current density criterion at room temperature (RT). The effect of temperature on the field emission properties of the SmB₆ nanowires has also been investigated. The turn-on field of the SmB₆ nanowires is found to decrease from 4.2 to 2.7 V μm^-1 (at 10 μA cm^-2); meanwhile, the estimated field enhancement factor increases from 2207 to 4741 clearly with an increase from RT to 573 K. This dependence might be due to the change in the effective work function of the nanowires with temperature.

[en] We report on the systematic investigation of optoelectronic properties of tin (IV) sulfide (SnS) van der Waals epitaxies (vdWEs) grown by molecular beam epitaxy (MBE) technique. Energy band simulation using commercial CASTEP code indicates that SnS has an indirect bandgap of size 0.982 eV. Furthermore, our simulation shows that elemental Cu can be used as a p-type dopant for the material. Growth of high quality SnS thin films is accomplished by MBE technique using graphene as the buffer layer. We observed significant reduction in the rocking curve FWHM over the existing published values. Crystallite size in the range of 2-3 μm is observed which is also significantly better than the existing results. Measurement of the absorption coefficient, α, is performed using a Hitachi U-4100 Spectrophotometer system which demonstrate large values of α of the order of 10⁴ cm^-1. Sharp cutoff in the values of α, as a function of energy, is observed for the films grown using a graphene buffer layer indicating low concentration of localized states in the bandgap. Cu-doping is achieved by co-evaporation technique. It is demonstrated that the hole concentration of the films can be controlled between 10¹⁶ cm^-3 and 5 x 10¹⁷cm^-3 by varying the temperature of the Cu K-cell. Hole mobility as high as 81 cm²V^-1s^-1 is observed for SnS films on graphene/GaAs(100) substrates. The improvements in the physical properties of the films are attributed to the unique layered structure and chemically saturated bonds at the surface for both SnS and the graphene buffer layer. Consequently, the interaction between the SnS thin films and the graphene buffer layer is dominated by van der Waals force and structural defects at the interface, such as dangling bonds or dislocations, are substantially reduced.

[en] In this study, the use of flexographic printing was investigated for low cost, high volume production of devices incorporating nanowires through the printing of zinc acetate precursors on a substrate used to form zinc oxide (ZnO) seeds for the growth of nanowires using a hydrothermal growth technique. The printing of precursors allows the selective area growth of ZnO nanowires, which has implications in high-yield production of devices incorporating ZnO nanowires. The work presented here achieved printed line widths of <60 μm with low edge distortion (<3 μm) using a printing plate with a line width of 50 μm. The hydrothermally grown ZnO nanowires show uniform density of growth over the printed area with nanowire diameters between 40 and 60 nm on both silicon and polyimide substrates. Energy-dispersive x-ray spectra showed contamination-free crystals with a 1:1 (zinc to oxygen) stoichiometry. Crystal orientation is along the c-axis with high quality crystalline structure shown using x-ray diffraction spectroscopy and high resolution transmission electron microscopy. A ZnO nanowire gas sensor, fabricated using the flexographic printing technique, is demonstrated. Such a printing-assisted fabrication offers low cost, high volume production of devices incorporating ZnO nanowires, ranging from gas sensors to field emission devices. (paper)

[en] AlN ferromagnetic nanorods with 5 at.% of copper were studied by using x-ray absorption spectroscopy (XAFS) above the Cu K- and L3- edges. Theoretical simulations of XAFS spectra clearly identify a formation of small copper clusters inside AlN lattice. Average size of clusters was estimated to be 50-70 atoms from the analysis of both XANES (X-ray Absorption Near Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure) regions of spectra. Calculations of magnetic moments for different types of point copper defects in AlN lattice were made.

[en] Fe-doped AlN nanorods were studied by means of x-ray absorption spectroscopy above the Fe K- and L_2,3- edges. Theoretical simulations of the x-ray absorption spectra show that Fe atoms mainly substitute Al. A minor fraction of Fe interstitials or Fe-Al-N ternary alloy can be identified as well. Bader's AIM analysis predicts that neutral substitutional FeAl defect is in 2⁺ charge state, though Al in pure AlN is in 3⁺ charge state. Fe L_2,3 absorption spectra and photoluminescence data indicate the coexistence of Fe²⁺/Fe³⁺ in AlN:Fe nanorods so different charge states of substitutional Fe_Al should co-exist.