Results 1 - 10 of 85
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[en] Tape casting of BaFBr:Eu2+, an important storage phosphor material for X-ray detection was investigated. Rheological measurement, thickness evaluation and scanning electron microscopy were used to monitor the processes. Measurements of the physical imaging performance in terms of modulation transfer function, noise power spectrum and noise equivalent quanta were used to characterize the storage phosphor plates (SPPs). It was found that careful control of the processes, especially the optimization of the dispersants, resulted in superior SPPs with excellent packing structure and lowest structure noise. Measurements with a commercial Guinier Camera were also presented
[en] The relations of line peak intensity and width in IETS with the modulation parameter W = eVsub(s)/KT is presented to a great extent of W. The line quality factor Q (the ratio of line peak intensity to width) is introduced, as a paramenter for appraising line shape quality. In accordance with the relation of quality factor Q with W, the optimum measurement condition in IETS have been obtained. (orig.)
[en] We consider wetting phenomena in the vicinity of rough substrates. The quenched random geometry of the substrate is assumed to be a self-affine fractal with a roughness exponent of ζS. Asymptotic critical properties on approaching complete and critical wetting transitions are studied by combining the replica method with scaling and renormalization-group arguments. We find new critical behavior, controlled by a zero-temperature fixed point, when ζS exceeds the thermal roughness exponent of the emerging wetting layer. The possibility of an effective dimensional reduction due to randomness is considered. In two dimensions a number of exact results are obtained by using a many-body transfer-matrix technique
[en] The first-principles Hartree-Fock cluster method is applied to investigate the possible positions and associated hyperfine properties of the muonium centers in the II-VI semiconductor ZnO. Two clusters are used to simulate the local environments around the anti-bonding (AB)parallel and bond-center (BC)arallel muonium with axial symmetry along the c-axis, to try to understand the natures of the two centers whose axially symmetric hyperfine tensors have been observed experimentally. Our results show that the muonium center at the anti-bonding site close to oxygen (ABO)prallel is more stable and its charge state is +0.44, which indicates a donor state in the semiconductor, but the associated hyperfine parameters are only in reasonable order of magnitude agreement with the experiments. The results for the (BC)parallel center show a smaller binding energy than for the (ABO)parallel center, and hyperfine parameters three orders of magnitude larger than the experiment but still an order of magnitude smaller than for free muonium
[en] The defect formation energies and atomic geometries of interstitial hydrogen in its different charge states in a number of wide band gap oxides are calculated by the Heyd, Scuseria, Ernzerhof hybrid functional. As in semiconductors, two behaviours are found, it acts either as an amphoteric defect or as a shallow donor. There are large scale lattice relaxations between the different charge states for the case of the amphoteric defect. Interestingly, we find that the +/− transition level does have a good alignment below the vacuum level, as was found previously for tetrahedral semiconductors.
[en] External boundaries change the fluctuations of a correlated fluid, such as a liquid crystal, thereby causing long-range interactions. We compute how the interaction between two parallel plates is modified by the deformations of one plate. Corrections to the leading interaction decay with the average separation of the plates through an exponent related to the roughness of the boundary. These interactions may also modify the surface fluctuations of thin liquid films
[en] Highlights: • A new method of synthesizing Co-N films containing Co_4N phase. • Tunable magnetic properties achieved in ECR plasma CVD. • The change of magnetic properties is related to atoms mobility on substrate and the concentration of active species in plasma vapor. - Abstract: By introducing DC negative-biased Co target in the Electron Cyclotron Resonance (ECR) nitrogen/argon plasma, the Co-N films containing Co_4N phase were synthesized on Si(100) substrate. Effects of processing parameters on magnetic properties of the films are investigated. It is found that magnetic properties of Co-N films vary with N_2/Ar flow ratio, substrate temperature, and target biasing voltage. The saturation magnetization M_s decreased by increasing the N_2/Ar gas flow ratio or decreasing target biasing voltage, while the coercive field H_c increased, which is ascribed to the variation of relative concentration for N or Co active species in plasma vapor. The magnetic properties present complex dependency with growth temperature, which is related to the atom mobility on the substrate affected by the growth temperature. This study exhibits a potential of ECR plasma chemical vapor deposition to synthesize the interstitial compounds and tune magnetic properties of films.
[en] La0.67Ca0.33MnO3 films are known to release oxygen upon vacuum annealing due to lattice expansion caused by change of valence state of Mn from Mn4+ to Mn3+. RBS measurements using O(α,α) resonance reaction at 3.043 MeV show that oxygen concentration decreases from 60% to 57% in 450 deg. C-vacuum annealed samples. There is also oxygen loss from the SrTiO3 substrate up to a certain depth. The measure of crystalline quality χmin degrades from 5.9% to 10%. A 45 deg. in-plane orientation is observed which is due to the dominant presence of [1 1 0]0 texture in the epilayer. The measured channeling half width ψ1/2 decreases upon vacuum annealing. In the samples annealed in oxygen at high pressure at 700 deg. C, there is no measurable change in oxygen concentration and χmin improved to 4.4%. ψ1/2 increases upon high pressure oxygen annealing. Our measurements directly show that there is lattice disorder upon vacuum annealing and ordering upon high pressure oxygen annealing and it is the largest for the oxygen lattice sites
[en] Experimental observations of fractal growth at dendrite tips during crystalline-to-amorphous phase transition in an ion-irradiated Mo65Ni35 thin film are reported. It was found that the observed anisotropic fractal patterns were of DLA type but not exactly self-similar. The possible mechanism of this exception to the ordinary parabolic tip growth of the dendrites is discussed