Growth of ultrathin twin-free b-oriented YBa2Cu3O7–x films

Twin-free b-oriented YBa2Cu3O7–x films with a thickness less than 40 nm have been epitaxially grown on (100)SrLaGaO4 crystals. Based on the temperature dependence of resistance, the onset temperature of the transition to the superconducting state is found to be 90 K; the transition width is 4 K. The film growth has been performed in two stages. A (100)PrBa2Cu3O7 – x buffer layer was previously grown on a (100)SrLaGaO4 substrate by rf magnetron sputtering in an Ar–O2 gas mixture at a continuous and monotonic increase in temperature from 660 to 830°C. The main YBa2Cu3O7 – x film was grown on the buffer layer surface by pulsed laser deposition in an oxygen medium at a fixed temperature (800°C). The above processes were implemented in different chambers, which were connected by a vacuum channel for transporting samples. Both films were grown in situ, without contacting atmosphere in all growth stages. An X-ray diffraction study has shown that the YBa2Cu3O7 – x films are single-crystal and free of precipitates of other phases and domains of other orientations.