No abstract

No abstract

An international round robin test was promoted to establish a test method for room temperature mechanical properties of commercial REBCO superconductive tapes. Seven laboratories practiced a tensile test under the direction of guideline REBCO13 for four different kinds of REBCO tape. From the stress versus strain curve, the modulus of elasticity and the 0.2% proof strength were measured. The scatter of measured values was analyzed by evaluating the RSU (relative standard uncertainty). To judge the major contribution to scattering, an F test was applied. The major source of RSUs was estimated to be the influence of inter-laboratory scattering. In order to reduce the overall scattering, it is suggested that the REBCO13 guideline should be modified with respect to the following three experimental factors. The window determining acceptable data should be narrowed, and the initial strain rate should be suppressed to less than 1 × 10 −4 (s −1 ). Repeated thickness measurement is recommended to reduce the standard uncertainty.

No abstract

1 Introduction Nonpolar plane GaN layers, either m-plane {1 100} or a-plane {1120}, without internal electric fields are more suitable for the fabrication of highperformance optical and electronic devices than are polar c-plane GaN layers [1]. In order to realize the full potential of nonpolar characteristics, the use of freestanding nonpolar substrates with high crystal quality is indispensable. So far, the only nonpolar plane GaN wafers commercially available were small transverse slices of c-oriented bulk crystals grown by hydride vapor phase epitaxy (HVPE). There have been several attempts to grow large-diameter nonpolar wafers by HVPE on foreign materials such as LiAlO 2 [2-4]; however, further study is required to find a method that successfully prepares large-diameter nonpolar plane GaN wafers with low defect density.In this study, we report the preparation of a nonpolar plane freestanding GaN wafer with a diameter exceeding 45 mm by using a conventional m-plane sapphire wafer with the novel use of an Al 4 C 3 buffer layer. The crystal lattice arrangement between the m-plane sapphire, Al 4 C 3 layer, and m-plane GaN layer is clarified. The effect of the buffer layer growth condition on the appearance of the m-plane orientation was examined. Furthermore, we tried