Search results for "Nitride"
showing 10 items of 249 documents
LDA+Uand tight-binding electronic structure of InN nanowires
2013
In this paper we employ a combined ab initio and tight-binding approach to obtain the electronic and optical properties of hydrogenated Indium nitride InN nanowires. We first discuss InN band structure for the wurtzite structure calculated at the LDA+U level and use this information to extract the parameters needed for an empirical tight-binging implementation. These parameters are then employed to calculate the electronic and optical properties of InN nanowires in a diameter range that would not be affordable by ab initio techniques. The reliability of the large nanowires results is assessed by explicitly comparing the electronic structure of a small diameter wire studied both at LDA+U and…
In situ— High Temperature Mössbauer Spectroscopy of Iron Nitrides and Nitridoferrates
2003
The stoichiometric iron nitrides γ′-Fe4N, e-Fe3N and ζ-Fe2N were characterized by Mossbauer spectroscopy. The thermal decomposition of e-Fe3N was studied in-situ by means of a specially developed Mossbauer furnace. We found e-Fe3N to γ′-Fe4N and e-Fe3Nx (x ≥ 1.3) as decomposition products and determined the border of γ′/e transformation at T ≅ 930 K. Mossbauer spectroscopy was applied to study in-situ the thermal decomposition of the nitridometalate Li3[FeIIIN2] and the formation of Li2[(Li1-xFeIx)N], the compound with the largest local magnetic field ever observed in an iron containing material. The kinetics of formation and the stability of Li2[(Li1-xFeIx)N] was of particular interest in …
From nitrides to carbides: topotactic synthesis of the η-carbides Fe3Mo3C and Co3Mo3C
2004
The molybdenum bimetallic interstitial carbides Fe(3)Mo(3)C and Co(3)Mo(3)C have been synthesized by temperature-programmed reaction (TPR) between the molybdenum bimetallic interstitial nitrides Fe(3)Mo(3)N and Co(3)Mo(3)N and a flowing mixture of CH(4) and H(2) diluted in Ar. These compounds have been characterized by X-ray diffraction, laser Raman spectroscopy, elemental analysis, energy dispersive analysis of X rays, thermal analysis (in air) and scanning electron microscopy (field emission). Their structures have been refined from X-ray powder diffraction data. These carbides crystallize in the cubic system, space group Fd3m[a= 11.11376(6) and 11.0697(3)[Angstrom] for Fe and Co compound…
Monitoring the carburization of molybdenum bimetallic nitrides and oxynitrides with CH4/H2/Ar mixtures: identification of a new carbonitride.
2008
A new carbonitride Ni2Mo3(CxNy) has been synthesized by temperature-programmed carburization of the Ni2Mo3N precursor with a CH4/H2/Ar gas mixture at 923 K. This compound has been characterized by X-ray diffraction, elemental analysis, Auger electron spectroscopy, laser Raman spectroscopy, thermogravimetric analysis and field-emission scanning electron microscopy. Ni2Mo3(CxNy) crystallizes in the cubic space group P4(1)32, with a lattice parameter of a=6.64575(3) A, corresponding to the unusual filled beta-Mn structure. Its formation occurs by partial substitution of N by C via a topotactic and pseudomorphic reaction and its stability in air is higher that of Ni2Mo3N. A two-phase mixture wi…
Bonding Trends in Lewis Acid Adducts of S 4 N 4 – X‐ray Structure of TeCl 4 ·S 4 N 4
2006
Tetrasulfur tetranitride and tellurium tetrachloride react in dichloromethane to form a 1:1 adduct TeCl4·S4N4 (1). The crystal structure of 1 shows that TeCl4 is bonded to the S4N4 ring through a Te–N linkage. As a consequence, the transannular S···S bonds in S4N4 are broken and the molecule assumes an open, monocyclic conformation. The Te–N bond of 2.16(1) A is slightly longer than the single bond. The S–N bonds span a range of 1.55(1)–1.67(1) A. The adduct 1 was also characterized by mass spectrometry and Raman spectroscopy. The bonding and spectroscopic properties of 1 are compared by DFT calculations at the B3PW91/(RLC ECP) level of theory with those of BF3·S4N4 (2), SO3·S4N4 (3), AsF5·…
Solar blind AlGaN photodetectors with a very high spectral selectivity
2006
Solar blind detectors based on AlGaN heterostructures grown on sapphire by Molecular Beam Epitaxy and with a dielectric interference filter deposited on the back side are demonstrated to provide record spectral selectivity. Rejection ratios of 2 x 10(4), and better than 5 x 10(4), measured between 280 and 320 nm, are achieved in Metal Semiconductor Metal detectors and Schottky diodes respectively. The whole detector process is fully compatible with low cost array fabrication.
Atomic scale DFT simulations of point defects in uranium nitride
2007
Atomic scale density functional calculations are used to predict the behaviour of defects in uranium mononitride (UN). Two different density functional codes (VASP and CASTEP) were employed with supercells containing from 8 to 250 atoms (providing a significant range of defect concentrations). Schottky and nitrogen Frenkel point defect formation energies, local lattice relaxations and overall lattice parameter change, as well as the defect induced electronic density redistribution, are discussed.
Light harvesting with Ge quantum dots embedded in SiO2 and Si3N4
2014
Cataloged from PDF version of article. Germanium quantum dots (QDs) embedded in SiO2 or in Si3N4 have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850 degrees C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2 matrix, or in the 1-2 nm range in the Si3N4 matrix, as measured by transmission electron microscopy. Thus, Si3N4 matrix hosts Ge QDs at higher density and more closely spaced than SiO2 matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs e…
Study of titanium alloy Ti6242S oxidation behaviour in air at 560°C: Effect of oxygen dissolution on lattice parameters
2020
Abstract High temperature oxidation of titanium alloy Ti6242S was studied in air at 560 °C up to 10000 h. Oxidation kinetics obeys a parabolic law (kp = 8.7 × 10−15 g². cm−4.s-1). Oxygen dissolution in the metal was found to represent between 80 and 90% of the total mass gain. Thin oxide scales are mainly composed of TiO2, in top of which some alumina is present. Titanium nitride was detected as a very thin layer at the outer part of the metallic substrate. Underneath, the oxygen dissolution area was found to reach the maximum brittleness after 1000 h of oxidation.
Nitride-based heterostructures grown by MOCVD for near- and mid-infrared intersubband transitions
2007
Intersubband (lSB) optical absorption in different nitride-based heterostructures grown by metal-organic chemical vapour deposition (MOCVD) is reported. The role of indium in AlInN/GaN multi-quantum wells (MQWs) is investigated. At high concentration (15%) AlInN is quasi lattice-matched to GaN and no cracks appear in the structure. At very low indium concentration (similar to 2%) the material quality is improved without decreasing the ISB transition wavelength with respect to the case of indium-free structures. Different mechanisms of strain relaxation in pure and 2% indium-doped AlN/GaN MQW structures are also investigated. ISB transition wavelengths of 2 urn for AlN/GaN MQWs, and 3 mu n f…