Thick MgB2 film with (101) oriented micro-crystals

Very thick, 40 mum, clean, and highly textured MgB2,, film was effectively grown on an Al2O3 substrate. The fabrication technique was by the hybrid physical-chemical vapor deposition (HPCVD) using B2H6 gas and Mg ingot as the sources. The X-ray diffraction (XRD) analysis shows a highly (101)-oriented MgB2 crystal structure without any impurity detected. There is no signal from the substrate in the XRD spectrum, indicating that the film thickness has exceeded the X-ray penetration length. Scanning electron microscopy (SEM) reveals that the film is composed of highly packed MgB2 micro-crystals with a uniform size distribution of about 2 mum in diameter and 0.2 mum in thickness. According to the compositional analysis of energy-dispersive X-ray spectroscopy (EDX), no oxygen, hence no MgO, exists in the textured film, consistent with the XRD result. Also, the transport properties are similar to those of a single crystal, indicating a clean film of good crystallite. The zero field transition temperatures are determined as T-C(onset) = 39.2K and T-C(zero) = 38.4 K, giving a sharp transition typical of a clean sample. The residual resistivity ratio (RRR) is determined as 6.4 and the magnetoresistance (MR) is about 28% at 40 K under the applied field of 9 T, which are similar to those of a single crystal. The zero temperature upper critical field, H-C2(0), is extrapolated as 19 T from the T-C(onset) at applied field up to 9T. (C) 2004 Elsevier B.V. All rights reserved.