Electron-beam lithography and reactive ion etching have been used to fabricate thin-film Au/Nb bridges with widths ∼50 nm. The Au layer was used as both a mask for etching the Nb superconducting bridge and as a resistive shunt in the completed devices. Using these junctions, a dc superconducting quantum interference device (SQUID) design with a hole size of 200 nm×200 nm (nano-SQUID) has also been fabricated and characterized. A flux noise of approximately 7×10−6 Φ0/Hz1/2 at 4.2 K has been achieved, from which a calculated spin sensitivity of 250 spin/Hz1/2 is predicted.
Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.
Superconducting quantum interference filters (SQIFs) have been created using two dimensional arrays of YBCO step-edge Josephson junctions connected together in series and parallel configurations via superconducting loops with a range of loop areas and loop inductances. A SQIF response, as evidenced by a single large anti-peak at zero applied flux, is reported at 77 K for step-edge junction arrays with the junction number N = 1 000 up to 20 000. The SQIF sensitivity (slope of peak) increased linearly with N up to a maximum of 1530 V T−1. Array parameters related to geometry and average junction characteristics are investigated in order to understand and improve the SQIF performance in high temperature superconducting arrays. Initial investigations also focus on the effect of the SQUID inductance factor on the SQIF sensitivity by varying both the mean critical current and the mean inductance of the loops in the array. The RF response to a 30 MHz signal is demonstrated.
We have fabricated step edge junctions using MgO substrates and YBCO thin films. By varying the angle of the step edge over a range of angles up to 45", we have obtained 3 distinct step edge morphologies: a deep trench junction, a double junction and a single junction. We found that only the step angle and morphology affected the critical current density (I,) and that the film thickness-tostep height ratio had no effect over the range 0.2-1.1. Noise measurements indicated that the single junction steps had the lowest level of critical current fluctuations and the highest values of dynamic resistance. We have also studied the variation of I, with temperature and found it follows the Ambergaokar-Baratoff model with a lower zero energy gap. We use this information to confirm that the junction parameters are affected by the c-axis tilt and the in-plane orientations proposed by others and consider the transport mechanisms across the junction.
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