Study of YBa2Cu3O7-x films at various stages of their growth by medium-energy ion scattering

The initial stages in the formation and growth of yttrium-barium cuprate fi lms have been studied in the course of magnetron sputtering of a ceramic ta rget by combining medium-energy-ion scattering (MEIS) and scanning-electron microscopy. The growth mechanisms of YBa2Cu3O7-x films on MgO and substrat es having the perovskite structure, SrTiO3 and LaAlO3, at deposition temper atures of 700-780 degrees C and (Ar+O-2) pressure of similar to 70 Pa were found to be essentially different. Simulation of MEIS spectra (H+ or He+ io ns with initial energies of 150-250 keV) and comparison of these results wi th experimental data revealed that in the first case a film forms from pyra mid-shaped islands and, in the second, it grows by a two-dimensional layer- by-layer process starting practically with the first monolayer. For the isl and mechanism, MEIS permitted determination of the substrate surface covera ge and showed the growth of the YBa2Cu3O7-x phase to be paralleled by forma tion of epitaxial nuclei of a Cu2O phase. After the first, initial stage in the film formation, the second stage, regular growth within reduced thickn esses of 7-15 nm, sets in. This stage is characterized by a practically com plete coverage of the substrate and a stable composition. The third stage, regular growth, of an apparently helical nature, was observed to set in at thicknesses above 100 nm. In this stage, the quality of film structure in t he bulk and on the surface was found to be somewhat inferior to that of YBa 2Cu3O7-x single crystals and did not depend on substrate type. (C) 1999 Ame rican Institute of Physics. [S1063-7834(99)00604-8].