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Effect of oxygen partial pressure on the in situ growth of Y-Ba-Cu-O thin films on SrTiO 3

The evolution of YBCO film growth with thickness at various oxygen pressures was observed by in situ synchrotron x‐ray diffraction in real time. When the films were deposited at 2 A/s and 730 °C under higher oxygen partial pressures (in an Ar/O2 mixture of 90 mTorr), the nucleation was observed to have c‐axis orientation. After the films reached a critical thickness, the growth of the YBCO film changed from c axis to a axis and then propagated epitaxially. This provides evidence that a‐axis epitaxial growth nucleates on a c‐axis base. The critical thickness reflects the competition between the growth of the c and a axes, which is determined by the oxygen partial pressure in the process of thin‐film formation. The a‐axis oriented films showed a very sharp rocking curve (less than 0.1°) which indicates a very high structural quality. For very low oxygen partial pressures, the in situ growth process was very similar, but the initial nuclei involve a second phase mixed with a small amount of c‐axis ‘‘123’’ ph...