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Using first principles LSDA+U calculation, a systematic investigation of the role of the Hubbard potential U on the structural, magnetic and electronic properties of Co 2 TiSi and Co 2 TiSn Heusler alloys was conducted. The structural, magnetic and electronic properties of Co 2 TiSi and Co 2 TiSn were calculated at different values of Hubbard potentials for Co ( U Co ) and Ti (U Ti ) atoms. The calculated lattice parameters are found to be slightly underestimated when compared with the experimental values with insignificant dependence on both U Co and U Ti . While non integer magnetic moments and metallic behaviors were predicted by LSDA, LSDA+U predicted half metallic behaviors and magnetic moments of 2μ B , in agreement with Slater-Pauling rule, at relatively low values of U Co and U Ti . A strong dependence of the band gap ( E g ) on U Co and U Ti was found in the two systems. The E g ( U ) dependence is characterized by two distinct regions: first region shows increasing trend while second region shows saturation with the increase in the value of U Co . In the first region, the band gap is controlled by Co d - t 2g and Co d - e g suborbitals only, and U Ti plays no role in agreement with Glanakis et al. scheme. However, in the second region, the band gap is defined by the Co d - t 2g and Ti d - e g suborbitals. The band gaps of the alloys were also calculated using the modified Becke-Johnson (mBJ) method predicting values within the second regions. The role of U Co and U Ti in determining the E g of the two systems was discussed. [ABSTRACT FROM AUTHOR]

DC reactive magnetron sputtered Nb z Al y N x coatings with various Al contents ( y /( y + z )) ranging from 0 to 0.75 were deposited using different ratios of the currents applied to the Al and Nb targets in order to systematically control their chemical composition and crystalline structure, and to enhance their mechanical, tribological and thermal stability performance. The film microstructure and properties were assessed by various complementary techniques such as electron probe microanalysis, X-ray diffraction, nanoindentation, ball-on-disc test, and scanning electron microscopy. It was found that the solubility limit of Al in the NbN lattice is in the range 0.44 < y /( y + z ) < 0.60. The Nb z Al y N x coatings present low compressive residual stress (≤ 3 GPa), and their hardness increases up to 31 GPa with increasing y /( y + z ) up to 0.40. The observed hardening is attributed to the solid solution mechanism. For y /( y + z ) > 0.44, the hardness of the Nb z Al y N x coatings is reduced due to the formation of the soft hexagonal AlN phase. In addition, the coatings exhibit interesting tribological properties: the coefficient of friction is in the range of 0.74 to 0.85, and wear rate is in the range of 4.8–9.1 × 10 − 6 mm 3 /Nm. Thermal stability shows a dependence on the Al content; specifically, the Nb 0.33 Al 0.17 N 0.50 coating was found to be thermally stable up to 700 °C. [ABSTRACT FROM AUTHOR]

Vanadium oxide (VO x ) thin films were deposited at various substrate temperatures ( T s ) by spray pyrolysis technique using 0.05 M vanadyl acetylacetonate precursor. V 4 O 9 films are formed at T s = 300 °C, while mixed V 2 O 5 phases are formed at higher T s (400 and 500 °C). Annealing in forming gas of V 4 O 9 films shows the formation of higher content of thermochromic VO 2 phase than V 2 O 5 films. V 4 O 9 films show little higher electric resistivity ( ρ ), higher temperature coefficient of resistance ( TCR ), and higher thermal carrier activation energy ( E a ) than V 2 O 5 films. Annealed VO x films show a 2–3 order of magnitude change in ρ , optical transmission switch of 19–39%, and higher E a than the as deposited films. Annealed films deposited at T s = 500 °C presents a high TCR of −4.6%K −1 . Optical absorption, electronic transitions, and energy gaps of the formed VO x phases have been discussed in relation to its electronic band structure. [ABSTRACT FROM AUTHOR]

Amorphous LaNiO3 (a-LNO) and crystalline LaNiO3 (c-LNO) films were prepared by spraying an aqueous precursor solution of lanthanum and nickel chlorides on hot (450°C) fused silica substrates followed by annealing at high temperatures (550–850°C). Thermal analysis of a dried precursor indicated that a stable oxide phase is formed at 560°C with no distinct crystallization peak. Scanning electron microscopy (SEM) powered with energy-dispersive X-ray spectroscopy (EDX) of as-sprayed films showed rough surfaces with particulate-like deposits and incomplete pyrolysis chloride composition. No chloride contents were detected in annealed films. X-ray diffraction showed that films annealed at 550°C and 650°C were a-LNO and those annealed at 750°C and 850°C were c-LNO. The c-LNO phase was indexed as a single-phase perovskite structure with (110) orientation. SEM/EDX showed that a-LNO films have rough surfaces and c-LNO films have uniform crack-free smooth surfaces. Electrical properties measurements showed that c-LNO films have lower resistivity than a-LNO films and both types of LNO films have semiconductor resistant temperature dependence. The activation energy of electric conduction of a-LNO films was found to be much higher than that of c-LNO films. The optical transmittance and reflectance of the films were studied in the UV–visible–near IR range. The optical constants were obtained by modeling the measured transmission and reflection spectra. Because of the discrepancies in the morphology and in the physical properties of a-LNO and c-LNO films, the best fit modeling of transmission and reflection spectra was obtained by using different theoretical models and different geometrical configurations. While the Drude model accounting for larger carrier density was found to be significant for c-LNO, using the Bruggmann model and a configuration of a rough layer on top of a compact film was found to be significant for a-LNO. [ABSTRACT FROM AUTHOR]

Abstract: Corundum (hexagonal) structure indium tin oxide (h-ITO) nanocrystals have been synthesized by subjecting an aqueous solution of In and Sn chlorides (Sn/In 8wt.%) to a hydrothermal process followed by annealing at 450°C in forming gas for 1h. The annealing temperature was selected based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) of the dried precipitated powder, which showed a stable weight and phase at temperatures above 420°C. X-ray diffraction (XRD) patterns showed the formation of orthorhombic InOOH precipitates that is transformed, after annealing, into h-ITO nanocrystals with 32nm average crystal size. For nanostructure film deposition, dispersed sols of the prepared nanocrystals were spun coated on glass substrates. The films were densified by UV irradiation, whilst four-probe method was used to measure its sheet resistance. A sheet resistance as low as 10.6kΩ□ have been reached. Scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) showed that the films have high surface roughness and nanopores. The transmittance spectra of the nanostructure films were measured in the UV–vis–NIR wavelength range. In addition to its low resistivity, nanostructure h-ITO films showed a wide range of transparency. [Copyright &y& Elsevier]

Abstract: Melting behavior of as-deposited and recrystallized indium nanocrystals is studied using reflection high-energy electron diffraction in its transmission mode. Indium films with mean thickness ranging from 1.5 to 10 monolayers (ML) deposited on highly oriented graphite at different substrate temperatures are studied. Atomic force microscopy is used to study the crystal size and morphology of the as-deposited and recrystallized nanocrystals. As-deposited films are found to form shallow nanocrystals with a flat top surface of different shapes, while the recrystallized nanocrystals are formed in the more rounded polyhedral shape. The change in the diffraction pattern intensity with temperature is used to probe the melting of the nanocrystals. The melting point is found to be lower than that of the bulk for both types of films and extends over a temperature range due to nanocrystal size distribution. The as-deposited films show an end melting point nearly equal to that of the recrystallized films except for the 1.5-ML film which shows an end melting point ∼10 K lower than the recrystallized film. The deposition temperature is found to have a significant effect on the end melting point of as-deposited nanocrystals, while having a negligible effect on the end melting point of recrystallized nanocrystals. [Copyright &y& Elsevier]

Melting and solidification of indium nanocrystals grown on (002) highly oriented graphite is studied by reflection high-energy electron diffraction operating in a transmission mode through the outer shell of the nanocrystals. When recrystallized from the melt, evaporated indium grows as an ensemble of nanocrystals with particle size distribution that depends on the mean film thickness. Films with mean thickness from 0.5 to 34 ML are investigated. The intensity change of the diffraction pattern with temperature is used to probe the melting and solidification of the nanocrystals. The melting of indium nanocrystals starts at temperatures below the bulk melting temperature, depending on the size distribution of the nanocrystals. Melting continues over a temperature range extending up to that of bulk melting. The liquid skin model of melting and the homogenous melting model are shown to agree with the melting point size dependence. However, line profile analysis of the diffraction pattern shows a reduction in the crystalline volume within the probed shell at high temperatures. This indicates the formation of a liquid layer surrounding the nanocrystals and supports the liquid skin model. All films show supercooling by an amount that increases with the mean film thickness up to 6 ML and remains constant for films with larger mean thickness. [Copyright &y& Elsevier]

First principles calculations based on density functional theory (DFT) using TB-mBJ and SCAN + U methods were used to study the electronic and optical properties of the monoclinic VO 2 (M1) phase. TB-mBJ gives values of the energy gap (E g) and Δd || band splitting in agreement with experiments. Systematic investigation of SCAN + U, U varies from 0 to 10 eV, shows that agreement with experimental values of both E g and Δd || was achieved at U * = 5.75 eV. Moreover, TB-mBJ and SCAN + U * were able to reproduce frequency and polarization dependence of the optical constants that agree with the reported experimental results of the monoclinic VO2 (M1) phase. The high value of U needed to reproduce the experimental values of electronic and optical parameters of the monoclinic VO 2 (M1) phase is a strong indication that VO 2 is a Mott insulator and the Mott-Hubbard scheme plays an important role in the metal-insulator transition. • The electronic and optical properties of the insulating monoclinic VO 2 (M1) phase were studied using TB-mBJ and SCAN+ U. • The size of the energy gap (E g) and d || band splitting and some optical constants of the VO 2 (M1) phase were calculated. • TB-mBJ and SCAN+U gave E g and Δd|| band splitting values in agreement with experiments. • TB-mBJ and SCAN+U were able to predict the frequency and polarization dependence of n , a , ε 1 , ε 2 of the VO 2 (M1) phase. • The current calculations reveal that Mott-Hubbard electron correlation is dominant in the metal-insulator transition in VO 2. [ABSTRACT FROM AUTHOR]