Microwave and superconducting techniques for measurements on unconventional Josephson junctions

The frst part of the thesis describes the instrumentation, testing and analysis of a planar circuit designed for the measurement of the current-phase relationship of niobium-cobalt-insulator-niobium Josephson junctions. A detailed analysis method and fitting routine was developed but the results show that an irreducible mutual inductance places a limit on the accuracy of the chip for the intended measurement. The second part describes a study of the magnetic and microwave properties of a range of thin film niobium coplanar resonators with cobalt and normal metal layers. Magnetic measurements show a magnetic dead layer of 1.3 nm. The observed microwave losses are found to be two orders of magnitude higher than for high quality niobium films. Computer simulation shows that this is mainly due to conductive, rather than magnetic losses, and is in good agreement with the observed proportionality to cobalt thickness. Measurements of the temperature and magnetic field dependence of the losses and resonant frequency as a function of the cobalt thickness show no signs of the oscillatory thickness dependence reported in a number of other experiments. The temperature dependence of all films is found to be in good agreement with Mattis-Bardeen theory

A simple, space constrained NIRIM type reactor for chemical vapour deposition of diamond

In this paper the design of a simple, space constrained chemical vapour deposition reactor for diamond growth is detailed. Based on the design by NIRIM, the reactor is composed of a quartz discharge tube placed within a 2.45 GHz waveguide to create the conditions required for metastable growth of diamond. Utilising largely off-the-shelf components and a modular design, the reactor allows for easy modification, repair, and cleaning between growth runs. The elements of the reactor design are laid out with the CAD files, parts list, and control files made easily available to enable replication. Finally, the quality of nanocrystalline diamond films produced are studied with SEM and Raman spectroscopy, with the observation of clear faceting and a large diamond fraction suggesting the design offers deposition of diamond with minimal complexity

Superconducting Diamond on Silicon Nitride for Device Applications

Chemical vapour deposition (CVD) grown nanocrystalline diamond is an attractive material for the fabrication of devices. For some device architectures, optimisation of its growth on silicon nitride is essential. Here, the effects of three pre-growth surface treatments, often employed as cleaning methods of silicon nitride, were investigated. Such treatments provide control over the surface charge of the substrate through modification of the surface functionality, allowing for the optimisation of electrostatic diamond seeding densities. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) were used to analyse the silicon nitride surface following each treatment. Exposing silicon nitride to an oxygen plasma offered optimal surface conditions for the electrostatic self-assembly of a hydrogen-terminated diamond nanoparticle monolayer. The subsequent growth of boron-doped nanocrystalline diamond thin films on modified silicon nitride substrates under CVD conditions produced coalesced films for oxygen plasma and solvent treatments, whilst pin-holing of the diamond film was observed following RCA-1 treatment. The sharpest superconducting transition was observed for diamond grown on oxygen plasma treated silicon nitride, demonstrating it to be of the least structural disorder. Modifications to the substrate surface optimise the seeding and growth processes for the fabrication of diamond on silicon nitride devices

Evaluating the coefficient of thermal expansion of additive manufactured AlSi10Mg using microwave techniques

In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal microwave components. Here we focus on a 2.5 GHz microwave cavity resonator, manufactured by PBF from the alloy AlSi10Mg. Of particular interest is its thermal expansion coefficient, especially since many microwave applications for PBF produced components will be in satellite systems where extreme ranges of temperature are experienced. We exploit the inherent resonant frequency dependence on cavity geometry, using a number of TM cavity modes, to determine the thermal expansion coefficient over the temperature range 6–450 K. Our results compare well with literature values and show that the material under test exhibits lower thermal expansion when compared with a bulk aluminium alloy alternative (6063)

Superconducting boron doped nanocrystalline diamond microwave coplanar resonator

A superconducting boron doped nanocrystalline diamond (B-NCD) coplanar waveguide resonator (CPR) is presented for kinetic inductance ($L_k$) and penetration depth ($\lambda_{\rm{L}}$) measurements at microwave frequencies of 0.4 to 1.2 GHz and at temperatures below 3 K. Using a simplified effective medium CPR approach, this work demonstrates that thin granular B-NCD films ($t\approx$ 500 nm) on Si have a large penetration depth ($\lambda_{\rm{L}}\approx 4.3$ to 4.4 $\mu$m), and therefore an associated high kinetic inductance ($L_{k,\square} \approx$ 670 to 690 pH/$\square$). These values are much larger than those typically obtained for films on single crystal diamond which is likely due to the significant granularity of the nanocrystalline films. Based on the measured Q factors of the structure, the calculated surface resistance in this frequency range is found to be as low as $\approx$ 2 to 4 $\mu\Omega$ at $T<2$ K, demonstrating the potential for granular B-NCD for high quality factor superconducting microwave resonators and highly sensitive kinetic inductance detectors.Comment: First draf

Evaluating the coefficient of thermal expansion of additive manufactured AlSi10Mg using microwave techniques

In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal microwave components. Here we focus on a 2.5 GHz microwave cavity resonator, manufactured by PBF from the alloy AlSi10Mg. Of particular interest is its thermal expansion coefficient, especially since many microwave applications for PBF produced components will be in satellite systems where extreme ranges of temperature are experienced. We exploit the inherent resonant frequency dependence on cavity geometry, using a number of TM cavity modes, to determine the thermal expansion coefficient over the temperature range 6–450 K. Our results compare well with literature values and show that the material under test exhibits lower thermal expansion when compared with a bulk aluminium alloy alternative (6063)

Quantitative analysis of the interaction between a dc SQUID and an integrated micromechanical doubly clamped cantilever

We provide simulations to quantitatively describe the interaction between a dc superconducting quantum interference device (SQUID) and an integrated doubly clamped cantilever. The simulations have been performed using the SQUID equations described by the resistively and capacitively shunted junction model coupled to the equation of motion of a damped harmonic oscillator. We have chosen to investigate an existing experimental configuration and have explored the motion of the cantilever configuration and the reaction of the SQUID as a function of the voltage flux V(Φ) V(Φ) characteristics. We clearly observe the Lorentz force back-action interaction and demonstrate how a sharp transition state drives the system into a nonlinear-like regime and modulates the cantilever displacement amplitude, simply by tuning the SQUID parameters

Blue delayed luminescence emission in neutral nitrogen vacancy containing chemical vapor deposition synthetic diamond

Herein, the authors investigate the temperature‐dependent properties of delayed luminescence in an as‐grown nitrogen‐containing chemical vapor deposition synthetic diamond gemstone when excited above its bandgap. At room temperature, this gemstone exhibits delayed luminescence from nitrogen‐vacancy centers at 575 nm. However, at 77 K, the first recorded instance of a long‐lived delayed blue luminescence centered at ≈465 nm, accompanied by spectral peaks at 419, 455, and 499 nm is reported. By analyzing spectral and temporal data at different temperatures, it can be speculated on potential photophysical transitions. This discovery documents the initial observation of this delayed luminescence emission, contributing to the collective understanding of synthetic diamonds