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The characteristic x-ray emission direction of a material indicates the direction of the bonding orbitals and spatial symmetry of the electron orbitals. Accordingly, the intensity of x-ray emission, which varies with the direction of emission and crystal orientation, provides crucial information regarding anisotropic electronic structures. This study utilized angle-resolved soft x-ray emission spectroscopy (SXES) on a layered material, NaAlSi, to ascertain the spatial distribution of the valence electrons. Distinct alterations in the spectral intensity distributions were observed in the Al–L2,3 and Si–L2,3 spectra with respect to the emission angle. To interpret the anisotropic SXES spectra, the spatial distribution of each valence electronic state was simulated using first-principle calculations. Although the anisotropic emission intensity could not explain the symmetry of the spatial distributions of the isolated s and d atomic orbitals, the anisotropy of the SXES spectra could be interpreted as the spatial distribution of these orbitals when hybridized with p orbitals. Furthermore, the spectral structure corresponding to the electronic states near the Fermi level reflected the characteristics of the d orbitals. Therefore, angle-resolved SXES measurements can effectively discern the spatial distribution of hybridized electron orbitals with specific energy levels, which could enhance techniques related to electron distribution analysis, with potential applications in material science and electronic structure characterization. [ABSTRACT FROM AUTHOR]

Tantalum thin films sputtered on unheated silicon substrates are characterized with microwaves at around 10 GHz in a 10 mK environment. We show that the phase of tantalum with a body-centered cubic lattice (α-Ta) can be grown selectively by depositing a niobium buffer layer prior to a tantalum film. The physical properties of the films, such as superconducting transition temperature and crystallinity, change markedly with the addition of the buffer layer. Coplanar waveguide resonators based on the composite film exhibit significantly enhanced internal quality factors compared with a film without the buffer layer. The internal quality factor approaches 2 × 107 at a large-photon-number limit. While the quality factor decreases at the single-photon level owing to two-level system (TLS) loss, we have deduced that one of the causes of TLS loss is the amorphous silicon layer at the film–substrate interface, which originates from the substrate cleaning before the film deposition rather than the film itself. The temperature dependence of the internal quality factors shows a marked rise below 200 mK, suggesting the presence of TLS–TLS interactions. The present low-loss tantalum films can be deposited without substrate heating and thus have various potential applications in superconducting quantum electronics. [ABSTRACT FROM AUTHOR]

Voids in SiO2 films deposited on GaN were probed by using monoenergetic positron beams. The films were fabricated on GaN substrates by using plasma-enhanced chemical vapor deposition. The size and density of the voids in the films increased up to an annealing temperature of 800 °C and then decreased at 1000 °C. The observed annealing behaviors of the voids were attributed to the desorption of impurities incorporated during the deposition process and the shrinkage of the Si–O matrix by high-temperature annealing. Vacancy-type defects were introduced into the GaN substrate after 1000 °C annealing in O2 atmosphere due to the diffusion of Ga from the substrate to the SiO2 film. No out-diffusion of Ga into the SiO2 film was observed for the annealing in N2 atmosphere. Thus, the observed out-diffusion of Ga was attributed to the enhanced oxidation of GaN during the annealing in O2 atmosphere. The diffusion of positrons implanted into the GaN substrate toward the SiO2 film was suppressed by annealing, suggesting a decrease in the negative charges in the SiO2 film or near the SiO2/GaN interface. [ABSTRACT FROM AUTHOR]

Transparent conducting polycrystalline Ga-doped ZnO (GZO) films with different thicknesses were deposited on glass substrates at a substrate temperature of 200 °C by ion-plating deposition with direct current arc-discharge. The dependences of crystal structure, electrical, and optical properties of the GZO films on thickness have been systematically studied. Optical response due to free electrons of the GZO films was characterized in the photon energy range from 0.73 to 3.8 eV by spectroscopic ellipsometry (SE). The free electron response was expressed by the simple Drude model combined with the Tauc–Lorentz model. From the SE analysis and the results of Hall measurements, electron effective mass, m*, and optical mobility, μopt, of the GZO films were determined, based on the assumptions that the films are homogeneous and optically isotropic. By comparing the μopt and Hall mobility, μHall, an indication on the effect of ingrain and grain boundary scattering limiting the electron mobility has been obtained. Moreover, the variation in scattering mechanism causing thickness dependence of μHall was correlated with the development of polycrystalline grain structure. [ABSTRACT FROM AUTHOR]

The pulsed laser photolysis/pulsed laser-induced fluorescence technique has been applied to obtain rate coefficients for OH+CH[sub 3]C(O)CH[sub 3] and CD[sub 3]C(O)CD[sub 3] of k[sub H](298–832 K)=(3.99±0.40)×10[sup -24]T[sup 4.00] exp(453±44)/T and k[sub D](298–710 K)=(1.94±0.31)×10[sup -21]T[sup 3.17] exp(-529±68)/T cm[sup 3] molecule[sup -1] s[sup -1], respectively. Three pathways were characterized via the CBS–QB3 ab initio method to obtain complete basis set limits for coupled-cluster theory. Addition to form CH[sub 3]C(O)(OH)CH[sub 3], followed by dissociation to CH[sub 3]+CH[sub 3]C(O)OH, is negligibly slow. Variational transition state theory reveals that the dominant products are CH[sub 3]C(O)CH[sub 2]+H[sub 2]O formed by direct abstraction at higher temperatures and via a hydrogen-bonded complex below about 450 K. Inclusion of tunneling gives good accord with the observed kinetic isotope effect down to about 250 K. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The impact of nitridation on open spaces in thin AlONx films deposited by a reactive sputtering technique was studied by using monoenergetic positron beams. For AlONx films with x = 0%–15%, positrons were found to annihilate from trapped states in open spaces, which coexist intrinsically in an amorphous structure with three different sizes. Nitrogen incorporation into the Al2O3 film increased the size of the open spaces, and their density increased as the post-deposition annealing temperature increased. The effect of nitrogen incorporation, however, diminished at x = 25%. The observed change in the network structure was associated with the formation of a stable amorphous structure, which we could relate to the electrical properties of AlONx/SiO2/Si gate stacks. [ABSTRACT FROM AUTHOR]

The estimate of free surface velocity at the billet mold in magnetohydrodynamic calculation is important for steel surface quality. It is considered that the free surface velocity in the electromagnetic stirring operation is transferred through the wall, a boundary of the molten steel. Then the wall friction phenomena between the wall and the molten steel are modeled so as a wall friction, force is a function of wall velocity. The calculated velocity distribution in consideration of the wall friction in which the friction coefficient is estimated as 0.03 is in good agreement with the measured value. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low resistivity Ga-doped ZnO films were prepared on a glass substrate by ion plating with direct current arc discharge. Thickness dependent changes in the electrical properties of the films are reported, focusing on the thin films of less than 100 nm thickness. Structural analyses showed that the thinnest film of 30 nm thickness consists of well-oriented columnar grains normal to the substrate, and the resistivity was as low as 4.4×10-4 Ω cm. The changes in lattice strain and c-axis fluctuation with the growth of grains are also shown to be associated with the electrical properties. [ABSTRACT FROM AUTHOR]

The authors have studied the optical input interface for Nb single-flux-quantum (SFQ) circuits and demonstrated its operation using photomixing technique. Two tunable lasers of C band were used for photomixing. We adopted a multistage toggle flip-flop (TFF) circuit as the main part of the test circuit. As the first trial, we used lasers with wavelength difference of 0.044 nm at around 1550 nm, which corresponds to the laser beat frequency of 5.5 GHz. The output signals from the 13- and 14-stage TFFs were observed and it showed the input SFQ frequency of 5.5 GHz. Thus, the authors demonstrated the conversion of the optical signal to SFQ signal and succeeded in driving the SFQ circuit. [ABSTRACT FROM AUTHOR]