RHEED STUDY OF CRYSTAL-GROWTH OF HIGH-TEMPERATURE SUPERCONDUCTING OXIDES IN REACTIVE COEVAPORATION

We have found oscillations in the reflection high energy electron diffraction (RHEED) specular intensity during growth of the superconducting oxides, indicating that the growth of the oxides occurs in monomolecular layer by monomolecular layer mode. The film thickness has been exactly controlled by monitoring the RHEED oscillations which make it possible to form a one unit-cell layer and artificial superlattices as designed. The isolated ultrathin YBa2Cu3O7-x (YBCO) films sandwiched in between PrBa2Cu3O7-x. (PrBCO) layers were prepared by the growth interrupt technique using the RHEED intensity oscillations. A one unit-cell YBCO layer has a superconducting transition with onset temperature at 70K and zero resistance at 30K. The overlayer of PrBCO was required to give the underlying one unit-cell YBCO superconductivity. The resistive transition for one unit-cell YBCO layer and the YBCO (one unit cell) / PrBCO (one unit cell) superlattice was independent of the magnetic field up to 10T applied parallel to the CuO2 layers.