High-quality ĉ-axis oriented thin films have been grown in situ on (100) surfaces of ZrO2 , SrTiO3 , and MgO. Sharp transitions to superconductivity were observed with Tc,off of 87–89.5 K for films thicker than 70 Å. The critical current density at 77.3 K was found to be strongly dependent on the film thickness. A maximum value was found for a 100-Å film with 8×106 A/cm2 at 77.3 K. On atomically flat single-crystal MgO substrates, films as thin as 15 Å revealed a full transition to superconductivity above 45.5 K. The superconducting properties of the films turned out to be quite insensitive to the deposition parameters, such as substrate temperature, oxygen partial pressure, sputter power, etc.
Microbridges with widths of about 10 μm were lift-off structured from rf-sputtered YBaCuO thin films and irradiated with microwaves at different temperatures. The bridges contain only a few grains with a typical size of 4 μm and are fully c-axis oriented. The observed current-voltage characteristics exhibit sharp constant voltage steps up to 71 K. An oscillatory dependence of the critical current I0 and the step heights 2In is observed, clearly revealing Josephson-like behavior. From the grain structure, the critical current, and the microwave response, it is very likely that grain boundaries as superconductor-normal conductor-superconductor (SNS) contacts dominate the behavior of the bridges.
Highly textured and polycrystalline YBaCuO thin films were sputtered on cold MgO single-crystal substrates. After annealing in oxygen for 1 h at 920 °C, the films show critical temperatures Tc,end up to 74.5 K. Superconducting quantum interference devices (dc SQUID’s) structured in ≊1-μm-thick polycrystalline films with a lift-off technique exhibit a critical current of 2 mA at 5.5 K and 35 μA at 72 K. Voltage modulation can be observed at temperatures up to 63 K.
Highly textured YBaCuO thin films were sputtered on MgO (100)-oriented single crystal substrates at ambient temperature followed by an anneal in oxygen for 1 h at temperatures up to 920~ X-ray diffractograms of the highly textured films indicate an orientation of the e-axis of the YBaCuO lattice perpendicular to the substrate surface. There are strong indications that the oriented caxis growth is due to a CuO self-flux effect. Auger measurements reveal a copper diffusion profile into the substrate down to a depth of more than 400 rim.
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