Study of the oxygen depletion in the film-substrate interface of superconducting YBa2Cu3O7−x films

Auger electron spectroscopy (AES) depth profiles were carried out on c-axis oriented YBa2Cu3O7−x films grown in situ onto SrTiO3 (100) and polycrystalline yttria-stabilized zirconia substrates. These films were grown by on-axis single-target dc planar magnetron sputtering, and they show zero resistance as high as 90.2 K and critical currents above 105 A/cm2 (77 K). The AES depth profiles reveal a clear oxygen loss at the interface. This oxygen deficiency corresponds to an atomic decrease from 7 to 6.6–6.3 per unit cell, in good agreement with the tetragonal structure oxygen composition. This confirms the oxygen-deficient first stages of YBa2Cu3O7−x film growth on some usual cubic substrates, and that those first layers do not become fully oxidized after the oxygen intake on the cooling in O2 atmosphere.