Interface effects on YBa₂Cu₃O_7-δ ultrathin film growth monitored by in situ resistance measurement

The growth dynamics of pulsed laser deposited ultrathin YBa ₂Cu₃O_7-δ films on various substrates was explored using an in situ resistance measurement technique. The results indicate that an interface region exists before the onset of uniform growth. On MgO and YSZ substrates, the first 30-50 Å has a small contribution to the conductivity of the film. This interface layer is less than one unit cell thick on better lattice-matched substrates, such as SrTiO₃, LaAlO ₃, and CeO₂. The thinnest interface layer was found on PrBa₂Cu₃O_7-δ. Misfit strain relaxation and island growth mechanism can be used to explain experimental observations. The superconductivity degradation for ultrathin YBa₂Cu ₃O_7-δ films is also discussed. In situ resistance measurement can be an excellent method to study the ultrathin film growth mechanism.