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81.
B. Prasanna Lakshmi V. Rajagopal Reddy V. Janardhanam M. Siva Pratap Reddy Jung-Hee Lee 《Applied Physics A: Materials Science & Processing》2013,113(3):713-722
We report on the effect of an annealing temperature on the electrical properties of Au/Ta2O5/n-GaN metal–insulator–semiconductor (MIS) structure by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The measured Schottky barrier height (Φ bo) and ideality factor n values of the as-deposited Au/Ta2O5/n-GaN MIS structure are 0.93 eV (I–V) and 1.19. The barrier height (BH) increases to 1.03 eV and ideality factor decreases to 1.13 upon annealing at 500 °C for 1 min under nitrogen ambient. When the contact is annealed at 600 °C, the barrier height decreases and the ideality factor increases to 0.99 eV and 1.15. The barrier heights obtained from the C–V measurements are higher than those obtained from I–V measurements, and this indicates the existence of spatial inhomogeneity at the interface. Cheung’s functions are also used to calculate the barrier height (Φ bo), ideality factor (n), and series resistance (R s ) of the Au/Ta2O5/n-GaN MIS structure. Investigations reveal that the Schottky emission is the dominant mechanism and the Poole–Frenkel emission occurs only in the high voltage region. The energy distribution of interface states is determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height. It is observed that the density value of interface states for the annealed samples with interfacial layer is lower than that of the density value of interface states of the as-deposited sample. 相似文献
82.
This paper deals with the preparation and optical analysis of Er3+ (0.2 mol%) boro-fluoro-phosphate glasses in the following glass compositions:
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Series A: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 AlF3
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Series B: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 LiF
83.
Electron Spin Resonance (ESR) spectra of gamma irradiated methylacrylamide-2-acrylamido-2-methyl-propanesulphonic acid (MA-AMPS) are recorded to identify the radical species formed during the irradiation of the copolymer. The ESR spectrum observed for irradiated MA-AMPS copolymer at liquid nitrogen temperature (LNT) (77 r K) is an asymmetric triplet; while the spectrum observed at room temperature (RT) is a quintet. The intensity distribution of both the spectra deviated appreciably from the expected theoretical values. Computer simulations are employed to analyze the ESR spectra observed at different temperatures. The triplet spectrum observed at LNT is simulated to be a superposition of component spectra arising from macroradicals of the type~CH 2 - \dot {\rm C} H-CH 2 ~ (I), radicals of the type \dot {\rm C} H 2 SO 3 H (II), and peroxy radicals (III). In contrast, the RT spectrum is simulated to be a superposition of component spectra arising due to radicals I, II, III together with the component quartet assigned to methyl radicals ( \dot {\rm C} H 3 ). The formation of such free radicals in irradiated copolymer is discussed. 相似文献
84.
Su Jin Han Hyung-Il Lee Byung Kyu Kim Anjanapura V. Raghu Kakarla Raghava Reddy 《Journal of Macromolecular Science: Physics》2014,53(7):1193-1204
Graphene, prepared by the thermal reduction of graphite oxide (GO), was modified with stearic acid to enhance its lipophilicity. A novel method, using the intrinsic epoxy groups on the graphene, was utilized for reaction with stearic acid to minimize the negative impact of the normal functionalization method on the π-electronic system of graphene. Gravimetric analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the stearic acid was effectively attached to the graphene. In addition, Raman spectroscopy and electric conductivity of the graphene showed that this novel modification method, utilizing intrinsic defects, did not damage the π-electronic system of the sp2 bonded carbons. The dispersion of graphene in a low density polyethylene (LDPE) matrix was enhanced; consequently, the reinforcing effect in tensile testing was improved by the lipophilic modification. The crystallization behavior observed by differential scanning calorimetry (DSC) showed that the crystallization of LDPE was hindered by dispersed graphene, more evidently when dispersed uniformly. 相似文献
85.
R.V.S.S.N Ravikumar R Komatsu A.V Chandrasekhar Y.P Reddy 《Journal of Physics and Chemistry of Solids》2003,64(2):261-264
Electron paramagnetic resonance and optical investigations of copper and chromium doped LiRbB4O7 glasses are carried out. From the results and discussions, it is predicted that both the transition metal ions exhibit octahedral environment. In the case of Cr3+, the site symmetry is near octahedral, whereas in the case of Cu2+, it is tetragonally distorted octahedral environment. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. The bonding parameters are suggesting ionic. 相似文献
86.
Charagundla SR Borthakur A Leigh JS Reddy R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,162(1):113-121
Significant artifacts arise in T(1rho)-weighted imaging when nutation angles suffer small deviations from their expected values. These artifacts vary with spin-locking time and amplitude, severely limiting attempts to perform quantitative imaging or measurement of T(1rho) relaxation times. A theoretical model explaining the origin of these artifacts is presented in the context of a T(1rho)-prepared fast spin-echo imaging sequence. Experimentally obtained artifacts are compared to those predicted by theory and related to B(1) inhomogeneity. Finally, a "self-compensating" spin-locking preparatory pulse cluster is presented, in which the second half of the spin-locking pulse is phase-shifted by 180 degrees. Use of this pulse sequence maintains relatively uniform signal intensity despite large variations in flip angle, greatly reducing artifacts in T(1rho)-weighted imaging. 相似文献
87.
We consider the application of least-squares finite element models combined with spectral/hp methods for the numerical solution of viscous flow problems. The paper presents the formulation, validation, and application of a spectral/hp algorithm to the numerical solution of the Navier–Stokes equations governing two- and three-dimensional stationary incompressible and low-speed compressible flows. The Navier–Stokes equations are expressed as an equivalent set of first-order equations by introducing vorticity or velocity gradients as additional independent variables and the least-squares method is used to develop the finite element model. High-order element expansions are used to construct the discrete model. The discrete model thus obtained is linearized by Newton’s method, resulting in a linear system of equations with a symmetric positive definite coefficient matrix that is solved in a fully coupled manner by a preconditioned conjugate gradient method. Spectral convergence of the L2 least-squares functional and L2 error norms is verified using smooth solutions to the two-dimensional stationary Poisson and incompressible Navier–Stokes equations. Numerical results for flow over a backward-facing step, steady flow past a circular cylinder, three-dimensional lid-driven cavity flow, and compressible buoyant flow inside a square enclosure are presented to demonstrate the predictive capability and robustness of the proposed formulation. 相似文献
88.
W. Brullot N.K. Reddy J. Wouters V.K. Valev B. Goderis J. Vermant T. Verbiest 《Journal of magnetism and magnetic materials》2012
Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles were obtained by a facile protocol and thoroughly characterized. Superparamagnetic iron oxide nanoparticles synthesized using a modified forced hydrolysis method were functionalized with polyethylene glycol silane (PEG silane), precipitated and dried. These functionalized particles are dispersable in a range of solvents and concentrations depending on the desired properties. Examples of tunable properties are magnetic behavior, optical and magneto-optical response, thermal features and rheological behavior. As such, PEG silane functionalized particles represent a platform for the development of new materials that have broad applicability in e.g. biomedical, industrial or photonic environments. Magnetic, optical, magneto-optical, thermal and rheological properties of several ferrofluids based on PEG coated particles with different concentrations of particles dispersed in low molecular mass polyethylene glycol were investigated, establishing the applicability of such materials. 相似文献
89.
Jitendra Pal Singh Gagan Dixit R.C. Srivastava H.M. Agrawal V.R. Reddy Ajay Gupta 《Journal of magnetism and magnetic materials》2012
We investigated the magnetic behavior of nanosized zinc ferrite with the help of vibrating sample magnetometry and in-field Mössbauer spectroscopy. The nanoparticles of zinc ferrite with crystallite size ranging from 10 to 62 nm were synthesized by a nitrate method. The structure and phase were determined with the help of X-ray diffraction. Attributes of cation inversion were found with the calculated values of lattice parameter. The saturation magnetization decreases with the increase in crystallite size at room temperature, while these values are almost the same at 10 K for all the samples except the one with crystallite size of 10 nm. The thermal magnetization measurement shows a decrease in blocking temperature with increase in particle size for these samples. The synthesized samples exhibit the presence of antiferromagnetic ordering below the blocking temperature as investigated by in-field Mössbauer spectroscopy. 相似文献
90.
Polyaniline-modified tin oxide and tin oxide nanoparticles were synthesized using a solution route technique. The obtained
pristine products were characterized with X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and
optical absorption spectroscopy. Thermogravimetric analysis results showed that the polyaniline-modified SnO2 nanoparticles exhibit higher thermal stability than the SnO2 nanoparticles. Scanning electron microscopy analysis on the as-synthesized powders showed spherical particle in the range
of 50–100 nm. 相似文献