Material considerations for the development of superconducting boron doped nanocrystalline diamond devices

Manifold, Scott 2022. Material considerations for the development of superconducting boron doped nanocrystalline diamond devices. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The work in this thesis is part of an ongoing project concerned with the development of superconducting devices using boron doped nanocrystalline diamond (B-NCD). Two aspects of device development were the focus of this work: the fabrication of low resistance ohmic metal electrical contacts and the investigation of the physics B-NCD Josephson junctions. The contact resistance of titanium, chromium, molybdenum, tantalum and palladium contacts was investigated between 1.9 and 300 K. All contacts showed mechanical stability, robust to several temperature sweeps. All contact schemes remained ohmic throughout and showed low resistances ranging from Ti/Pt/Au with (8.83+/-0.10) x 10−4 Ohm.cm to Ta/Pt/Au with (8.07+/-0.62) x 10-6 Ohm.cm. The candidate Josephson junction devices were investigated both in varying temperature and field. The temperature dependence of the superconducting gap and critical currents I_c showed strong agreement across all device types and geometries, with all being well described by standard BCS theory and the model proposed by Ambegaokar and Baratoff. Fluctuation spectroscopy analysis was performed on temperature dependent conductance data from three structures, confirming that the effects of the material’s granularity on the superconductivity still dominate in the smaller geometries of the devices. The field dependence of the critical currents for all devices was again insensitive to device type or geometry and does not conform to the expected Fraunhofer diffraction pattern. Instead, using the grain size distribution to provide the magnetically transparent dimensions of the junctions, a model was developed that accounts for the power law type drop off in I_c (B). Given the results above, it is impossible for the geometry of the devices to be determining their behaviour. Instead, the distribution of grain sizes in the devices is what governs the physics of the Josephson junctions.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Superconductivity superconducting devices Josephson junctions diamond boron doped nanocrystalline diamond nanofabrication contact resistance diamond metallisation low temperature physics
Funders:	Engineering & Physical Sciences Research Council (EPSRC)
Date of First Compliant Deposit:	3 October 2023
Last Modified:	04 Oct 2023 11:39
URI:	https://orca.cardiff.ac.uk/id/eprint/162917

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