Thermal, structural and optical properties of NiOx thin films deposited by reactive dc-magnetron sputtering

The NiOx thin films were deposited by reactive dc-magnetron sputtering from a nickel metal target in Ar + O-2 with the relative O-2 content 5%. The as-deposited NiOx, thin films could represent a two-component system comprising crystalline NiO particles dispersed in an amorphous Ni2O3. Decomposition temperature of the as-deposited NiO, thin films was at about 263 degrees C. After annealed at 400 degrees C for 30 min in air, the surface morphology of the films became very rough due to the decomposition of the Ni2O3, leading to the changes of the optical properties of the NiO, thin films. The reflectivity of the films annealed at 400 degrees C was lower than that of the as-deposited one and the optical contrast was 52% at 405 nm. (c) 2006 Elsevier B.V. All rights reserved.

Structural and optical properties of YAG : Ce3+ phosphors by sol-gel combustion method

High-quality Ce3+-doped Y3Al5O12 (YAG:Ce3+) phosphors were synthesized by a facile sol-gel combustion method. In this sol-gel combustion process, citric acid acts as a fuel for combustion, traps the constituent cations and reduces the diffusion length of the precursors. The XRD and FT-IR results show that YAG phase can form through sintering at 900 degrees C for 2 h. This temperature is much lower than that required to synthesize YAG phase via the solid-state reaction method. There were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) observed in the sintering process. The average grain size of the phosphors sintered at 900-1100 degrees C is about 40 nm. With the increasing of sintering temperature, the emission intensity increases due to the improved crystalline and homogeneous distribution of Ce3+ ions. A blue shift has been observed in the Ce3+ emission spectrum of YAG:Ce3+ phosphors with increasing sintering temperatures from 900 to 1200 degrees C. It can be explained that the decrease of lattice constant affects the crystal field around Ce3+ ions. The emission intensity of 0.06Ce-doped YAG phosphors is much higher than that of the 0.04Ce and 0.02Ce ones. The red-shift at higher Ce3+ concentrations may be Ce-Ce interactions or variations in the unit cell parameters between YAG:Ce3+ and YAG. It can be concluded that the sol-gel combustion synthesis method provides a good distribution of Ce3+ activators at the molecular level in YAG matrix. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis and magnetic properties of Ni-doped zinc oxide powders

Polycrystalline Zn1-xNixO diluted magnetic semiconductors have been successfully synthesized by an auto-combustion method. X-ray diffraction measurements indicated that the 5 at% Ni-cloped ZnO had the pure wurtzite structure. Refinements of cell parameters from powder diffraction data revealed that the cell parameters of Zn0.95Ni0.05O were a little bit larger than ZnO. Transmission electron microscopy observation showed that the as-synthesized powders were of the size similar to 60 nm. Magnetic investigations showed that the nanocystalline Zn0.95Ni0.05O possessed room temperature ferromagnetisin with the saturation magnetic moment of 0.1 emu/g (0.29 mu(B)/Ni2+). (c) 2005 Elsevier B.V. All rights reserved.

Structural and optical properties of a-plane ZnO thin films synthesized on γ-LiAlO2 (302) substrates by low pressure metal-organic chemical vapor deposition

Nonpolar a-plane (1120) ZnO thin films have been fabricated on gamma-LiAlO2 (302) substrates via the low-pressure metal-organic chemical vapor deposition. An obvious intensity variation of the E-2 mode in the Raman spectra indicates that there exhibits in-plane optical anisotropy in the a-plane ZnO thin films. Highly-oriented uniform grains of rectangular shape can be seen from the atomic force microscopy images, which mean that the lateral growth rate of the thin films is also anisotropic. It is demonstrated experimentally that a buffer layer deposited at a low temperature (200 degrees C) can improve the structural and optical properties of the epilayer to a large extent. (c) 2007 Elsevier B.V. All rights reserved.

Structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs on gamma-LiAlO2

We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a gamma-LiAlO2 (100) substrate. The TMGa, TMIn and NH3 are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10 x 10 mu m(2) by AFM scan area. The XRD spectra show that the materials grown on gamma-LiAlO2 (100) have < 1 - 100 > m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown on the gamma-LiAlO2 substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on voltage of 1-3 V.

Structure and magnetic properties of CoNiP nanowire arrays embedded in AAO template

Ternary CoNiP nanowire (NW) arrays have been synthesized by electrochemical deposition inside the nanochannels of anodic aluminum oxide (AAO) template. The CoNiP NWs deposited at room temperature present soft magnetic properties, with both parallel and perpendicular coercivities less than 500 Oe. In contrast, as the electrolyte temperature (T-elc) increases from 323 to 343 K, the NWs exhibit hard magnetic properties with coercivities in the range of 1000-2500 Oe. This dramatic increase in coercivities can be attributed to the domain wall pinning that is related to the formation of Ni and Co nanocrystallites and the increase of P content. The parallel coercivity (i.e. the applied field perpendicular to the membrane surface) maximum as high as 2500 Oe with squareness ratio up to 0.8 is achieved at the electrolyte temperature of 328 K. It has been demonstrated that the parallel coercivity of CoNiP NWs can be tuned in a wide range of 200-2500 Oe by controlling the electrolyte temperature, providing an easy way to control magnetic properties and thereby for their integration with magnetic-micro-electromechanical systems (MEMS). (C) 2008 Elsevier B.V. All rights reserved.

Structural and optical properties of nanostructured TiO2 thin films fabricated by glancing angle deposition

TiO2 films deposited by electron beam evaporation with glancing angle deposition (GLAD) technique were reported. The influence of flux angle on the surface morphology and the microstructure was investigated by scanning electron microscopy. The GLAD TiO2 films are anisotropy with highly orientated nanostructure of the slanted columns. With the increase of flux angle, refractive index and packing density decrease. This is caused by the shadowing effect dominating film growth. The anisotropic structure of TiO2 films results in optical birefringence, which reaches its maximum at the flux angle alpha = 65 degrees. The maximum birefringence of GLAD TiO2 films is higher than that of common bulk materials. It is suggested that glancing angle deposition may offer an effective method to obtain tailorable refractive index and birefringence in a large continuous range. (c) 2006 Elsevier B.V. All rights reserved.

Mild Hydrothermal Synthesis, Crystal Structure, Thermal Behavior, Spectroscopic and Magnetic Properties of (NH4)0.80Li0.20[Fe(AsO4)F]

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Luminescence and Magnetic Properties of Two Three -Dimensional Terbium and Dysprosium MOFs Based on Azobenzene-4,4 '-Dicarboxylic Linker

We report the in situ formation of two novel metal-organic frameworks based on terbium and dysprosium ions using azobenzene-4,4-dicarboxylic acid (H(2)abd) as ligand, synthesized by soft hydrothermal routes. Both materials show isostructural three-dimensional networks with channels along a axis and display intense photoluminescence properties in the solid state at room temperature. Textural properties of the metal-organic frameworks (MOFs) have been fully characterized although no appreciable porosity was obtained. Magnetic properties of these materials were studied, highlighting the dysprosium material displays slightly frequency-dependent out of phase signals when measured under zero external field and under an applied field of 1000 Oe.

Growth and magnetic properties of ferromagnetic Co nanorods filled inside carbon nanotubes towards nanoscale spintronics

We synthesize Co nanorod filled inside multi-walled CNTs (MWCNTs) by microwave plasma enhanced chemical vapor deposition (MPECVD) and utilize off-axis electron holography to observe the remanent states of the filled metal nanorod inside MWCNTs at room. The MWCNTs grew up to 100-110 nm in diameter and 1.5-1.7 μm in length. The typical bright-field transmission electron microscope (TEM) images revealed both Co/Pd multisegment nanorod and Co nanorod filled inside MWCNTs on the same substrate. We have also performed energy-dispersive X-ray spectrometer (EDS) measurements to characterize the composition of metal filled inside MWCNTs. Based on high-resolution TEM measurements, we observed the face-centered-cubic (fcc) Co filled inside MWCNT. The component of magnetic induction was then measured to be 1.2±0.1 T, which is lower than the expected saturation magnetization of fcc Co of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states. © 2008 IEEE.

Structural and functional properties of the hemoglobin components from the Caspian Sea Acipenser persicus and Acipenser stellatus

Hemoglobin (Hb) variability is a commonly used index of phylogenetic differentiation and molecular adaptation in fish. In the current study, the structural and functional characteristics of Hbs from two Sturgeon species of the Southern Caspian Sea Basin were investigated. After extraction and separation of hemoglobin from whole blood , the polyacrylamide gel electrophoresis (SDSPAGE), native-PAGE and isoelectric focusing (IEF) were used to confirm Hb variability in these fishes. Ion-exchange on CM-cellulose chromatography was used for purification of the dominant Hbs from these fishes. The accuracy of the methods was confirmed by IEF and SDS-PAGE. Spectral studies using fluorescence spectrophotometery, circular dichroism spectropolarimetry (CD) analysis and UV–vis spectrophotometery. Oxygen affinities of these Hbs were compared using Hb-oxygen dissociation curves. Also, the dominant Hbs from these blood fishes were utilized for further experiments. The behavior of Hbs during the denaturation process by n-dodecyl trimethylammonium bromide (DTAB) is investigated by UV–vis spectrophotometer and circular dichroism spectropolarimetry. The thermal denaturation properties of the Hbs wereinvestigated by differential scanning calorimetry (DSC) and Hbs aggregation performed chemically in the presence of dithiotreitol (DTT) by UV–vis spectrophotometer and chemometric study. The results demonstrate a significant relationship between stability of fish hemoglobins and the ability of fish for entering to deeper depths. The UV–Vis absorption spectra identified species of hemoglobin and showed the concentration of oxyHb and metHb decreases and deoxyHb increases upon interaction with DTAB. Besides the UV–vis spectrophotometry, the interaction of DTAB with hemoglobins has been studied using circular dichroism spectropolarimetry analysis. This experiment was utilized to measure the unfolding mechanism and compared alpha-helix secondary structure under different conditions for Hbs. The results reveal that the Acipenser stellatus Hb in comparison with Acipenser persicus Hb has more stability and more structural compactness. Besides, the results confirm the hypothesis that there is a meaningful relation between average habitat depth, partial oxygen pressure, oxygen affinity, structural compactness of Hb, and its stability.

Electronic and magnetic properties of Ti(2)O(3), Cr(2)O(3), and Fe(2)O(3) calculated by the screened exchange hybrid density functional.

The electronic and magnetic properties of the transition metal sesqui-oxides Cr(2)O(3), Ti(2)O(3), and Fe(2)O(3) have been calculated using the screened exchange (sX) hybrid density functional. This functional is found to give a band structure, bandgap, and magnetic moment in better agreement with experiment than the local density approximation (LDA) or the LDA+U methods. Ti(2)O(3) is found to be a spin-paired insulator with a bandgap of 0.22 eV in the Ti d orbitals. Cr(2)O(3) in its anti-ferromagnetic phase is an intermediate charge transfer Mott-Hubbard insulator with an indirect bandgap of 3.31 eV. Fe(2)O(3), with anti-ferromagnetic order, is found to be a wide bandgap charge transfer semiconductor with a 2.41 eV gap. Interestingly sX outperforms the HSE functional for the bandgaps of these oxides.