X-ray absorption (XAS) and emission (XES) spectroscopy near B K and C K edges have been performed on metallic (ϳ0.1 at. % B, B-diamond) and semiconducting (ϳ0.03 at. % B and N, BN-diamond) doped diamond films. Both B K XAS and XES spectra show a metallic partial density of states (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of nondoped diamond: E V = 283.9 eV. C K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep and broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy ͑E a = 0.37 eV͒ estimated from the temperature dependence of the conductivity; namely, the change in C 2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is ascribed mainly to the electronic structure of C 2p near the Fermi level. The observed XES spectra are compared with the discrete variational X␣ (DVX␣) cluster calculation. The DVX␣ result supports the strong hybridization between B 2p and C 2p observed in XAS and XES spectra, and suggests that the small amount of boron ͑ഛ0.1 at. % ͒ in diamond occupies the substitutional site rather than interstitial site.

No abstract

X-ray emission (XES) and absorption (XAS) spectra near the B-K edge were measured on single-crystalline AlB2 compound which is an isostructural diboride of superconducting MgB2. The partial density of states (PDOS) of B-2pσ and pπ orbitals were derived from the polarization dependence of XES and XAS spectra. There are considerable amounts of PDOS near the Fermi energy in AlB2 similarly to that in MgB2, but there are almost no PDOS in pσ orbitals of AlB2 near the Fermi energy, i.e., a pseudo-gap in pσ state and a broad metallic state in pπ state are observed. The present result indirectly supports scenarios that the pσ holes play an important role in the occurrence of superconductivity in MgB2. The overall features of PDOS were found to be in good agreement with the result of band calculation of AlB2, but a small discrepancy in the Fermi energy is observed, which is attributed to the Al vacancy in the compounds, i.e., the estimated concentration is Al0.93B2. KEYWORDS: MgB 2 , AlB 2 , single crystal, partial density of state, pσ and pπ orbitals, X-ray emission and absorption spectroscopy

No abstract

Aluminum-doped diamond samples were synthesized using the conventional microwave plasma chemical vapor deposition method. The electronic structures were measured using an electron probe microanalyzer and by X-ray photoelectron spectroscopy. The area intensity of the partial profile of Al-3p near the Fermi level increased with increasing aluminum concentration in the sample. The partial profile of Al-3p resembles that of C-2p at high aluminum concentrations, which suggests strong hybridization between Al-3p and C-2p. Additionally, the temperature dependence of the electric resistance yields an activation energy of 8.2 meV at room temperature. The present results suggest the metal-insulator transition of aluminum-doped diamond, similar to that of boron-doped diamond. However, with increasing aluminum concentration, a considerable amount of carriers is not doped to C-2p orbitals in aluminum-doped diamond. The present results indicate that superconductivity in aluminum-doped diamond with the same mechanism as that in boron-doped diamond does not occur. Fig. 1. (Color online) Schematic view of stage, target, and Si substrate wafer in chamber used for MPCVD synthesis.

No abstract

In this paper, we describe the joining property of welded sheets obtained by magnetic pulse welding. In this method, it is possible to weld aluminum alloy sheets to a low-carbon sheet, for example, A6061-T6 or A2017-T3. An electromagnetic force deforms the aluminum sheet, and the height of the sheet is governed by both the force and the properties of the sheet. Collision times are examined in various gap lengths for the four kinds of aluminum sheets in 2.0 kJ discharge energy experiments, and collision velocities are calculated using the collision times. The relationship between shearing load of the welded sheet and the gap length is also examined. The collision times of the four sheets are approximately equal at gap lengths less than or equal to 2.48 mm and increase in accordance with the materials property values of quasi-static process at gap lengths more than 2.48 mm. Magnetic pulse welding is phenomenon in a high strain rate and the strain rate of the sheet exceeds 10000 s-1 as a rough estimate. It is difficult to weld the sheets with a large flow stress to the low-carbon sheet, and the welding depends on the flow stress. Therefore, the flow stress of aluminum sheet also is a factor influencing the joining property of welded sheets.

No abstract