The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

The sputter-induced epitaxy change of in-plane orientation occurring in YBa 2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-me tallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RES and TEM. The factors influencin g the orientation change are systematically studied. The experimental resul ts suggest that the substrate surface morphology change caused by the ion s puttering and the Ar ion implantation in the substrate surface layer are no t the major factors that affect the orientation change. Instead, the implan tation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studie s show that a BaxMg1-xO buffer layer is formed on top of the sputtered subs trate surface due to Ba diffusion into the W implanted layer. It is believe d that the formation of this buffer layer relieves the large lattice mismat ch and changes the YBCO film from the 45 degrees oriented growth to the 0 d egrees oriented growth.