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

Abstract

Twin-free b-oriented YBa₂Cu₃O_{7 – 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)PrBa₂Cu₃O_{7 – 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 YBa₂Cu₃O_{7 – 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 YBa₂Cu₃O_{7 – x} films are single-crystal and free of precipitates of other phases and domains of other orientations.