Mechanism and processing dependence of biaxial texture development in magnesium oxide thin films grown by inclined-substrate deposition

Biaxially textured thin films of MgO were deposited on metal foils as epitaxial template layers for high-T_c superconducting tapes. The MgO was deposited by electron beam evaporation on substrates inclined to the atomic vapor. The processing dependence of biaxial texture on inclination angle, deposition rate, film thickness, and substrate was investigated by four-circle X ray diffraction and selected-area electron diffraction. Texturing of the MgO was a selective growth process whereby the texture improves with increasing film thickness. This growth process differs from the texturing of MgO in ion-beam-assisted deposition, which is nucleation controlled and requires an amorphous substrate. It was experimentally found that the in-plane texture of the MgO thick films was not dependent on deposition rate from 2.5 to 100 Å/s, making this technique amenable to cost-effective production. This result has important implications to manufacturing scale-up of YBa₂Cu₃O_x coated tapes. The mechanism for the creation of biaxial texture in the MgO films was determined to be from the combined effects of the cubic equilibrium crystal habit of MgO and columnar self-shadowing