The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin nlHls of YBa2Cu307 -. The H, 2 results demonstrate the intrinsic anisotropy in this layered su-

We report the growth of in-plane textured (100) MgO on amorphous Si3N4 substrates by ion beam assisted deposition (IBAD). The textured MgO can be used as a structural template for subsequent epitaxial thin film deposition. The results are compared with IBAD of (100) and (111) yttria-stabilized-zirconia (YSZ). Based on transmission electron microscopy (TEM) and in situ reflection high energy-electron diffraction (RHEED), we find that MgO texturing is a nucleation-controlled process and the alignment is a function of nuclei size and density. This differs greatly from the evolutionary-type texturing process observed for IBAD (100) YSZ. Consequently, we are able to make 100 Å thick MgO films with 7° in-plane alignment, whereas IBAD (100) YSZ films need to be thicker than 5000 Å to achieve in-plane alignment better than 13°. This has important implications for the economical application of IBAD induced alignment in real manufacturing processes, including high Tc superconductor (i.e., YBCO) coated tapes, photovoltaics, magnetic thin films, and semiconductor devices.

7. A. Carillon eta/. . ibid. 68, 291 7 (1 992) 8. J A. Koch eta/. . ibid p 3291 9. L. B. Da S v a ei a/. , Opt Lett. 18, 11 74 (1 993).