No abstract

Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling

We demonstrate the feasibility of white organic light-emitting diodes that exclude the transparent conductor indium-tinoxide. Instead, a highly conductive Orgacon™ PEDOT:PSS material in combination with a metal support structure is used as transparent anode and hole-injection layer. The PEDOT:PSS exhibits a conductivity of 460±20 S/cm and a work function of 5.35±0.05 eV. On ITO-free OLEDs on glass with an active area of ~6 cm ² the inclusion of 120 nm thick printed metal lines reduces the variation in brightness from 35% to 20%. The ITO-free concept based on PEDOT:PSS with printed metal structures is scaled up to large flexible OLEDs with a size of 150 cm 2 on a heat-stabilized Teonex® Polyethylene Naphtalate foil. The voltage distribution across the various electrodes was verified by a finite element model, allowing a prediction of the OLED brightness and homogeneity over large areas.

Using an optimized bridge geometry we have been able to make accurate measurements of the properties of YBa 2 Cu 3 O 7-d grain boundaries above T c .The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band-bending at the boundary allows us to estimate the height of the potential barrier present at the grain boundary interface.

Submicron YBa2Cu3O7−x bicrystal grain boundary junctions have been fabricated, for the first time, by a focused ion beam process. Although such a process has always been considered detrimental to the YBa2Cu3O7−x because of gallium contamination, high quality 24° [001] tilt junctions characterized by RSJ current–voltage characteristics, ICRN products of the order of 1–4 × 104 A cm−2 at 77 K and Fraunhofer-like modulation patterns have been obtained. No significant degradation has been observed over more than 3 months. The critical current density JC and the characteristic voltage ICRN show a clear maximum for widths of the order of the Josephson penetration depth. The asymptotic normal resistance shows a typical (width)−1 dependence, indicating that the FIB process does not increase the grain boundary resistivity of submicron junctions. Experimental results clearly show that FIB is a very powerful tool for the fabrication of high critical temperature superconducting circuits, requiring a small number of submicron Josephson junctions, and for fundamental physics analysis. It also allow the final tuning or repair of superconducting or more complex integrated superconducting–semiconducting devices.