Grain size of nanocrystalline YSZ buffer layers fabricated by ion beam deposition

Amorphous or nanocrystalline thin films are capable to be efficient diffusion barrier layers for YBCO coated conductors of ion beam assisted deposition route. Nanocrystalline Yttria-Stabilized Zirconia (YSZ) buffer layers were fabricated by the ion beam deposition. Kr and Ar gases were utilized for the dual Kaufman type sputtering ion sources sequently. Both of the ion beams were fixed at 200 mA, while the ion energy was in the range of 450-2000 eV. The thickness of the YSZ buffer layers was several hundreds of nanometers. The grain size of YSZ thin films, which varied from 2 to 20 nm, was calculated by Scherrer Formulation based on the X-ray diffraction measurement results. The grain size always decreased at first and then increased when the ion energy was increased. In the cases Kr gas was utilized and Ar gas was utilized, the grain size reached its minimum value at the ion energy of about 1800 eV and 1000 eV, respectively. Such phenomenon was discussed using the thermodynamic theory of thin film nucleation. Deposition rate and substrate temperature were the two chief variables of the critical nuclei concentration and grain size.