Effect of oxygen partial pressure on the in situ growth of Y‐Ba‐Cu‐O thin films on SrTiO3

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...