Dr. Davie Mtsuko Profile

Dr. Davie Mtsuko

at Univ of the Witwatersrand

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Publications (2)

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Proceedings Article | 3 February 2017 Paper

Quantum device prospects of superconducting nanodiamond films

D. Mtsuko, D. Churochkin, S. Bhattacharyya

Proceedings Volume 10036, 1003606 (2017) https://doi.org/10.1117/12.2245593

KEYWORDS: Diamond, Carbon, Superconductors, Magnetism, Resistance, Scattering, Transition metals, Boron, Temperature metrology, Microwave radiation

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Nanostructured semiconducting carbon system, described by as a superlattice-like structure demonstrated its potential in switching device applications based on the quantum tunneling through the insulating carbon layer. This switching property can be enhanced further with the association of Josephson’s tunneling between two superconducting carbon (diamond) grains separated by a very thin layer of carbon which holds the structure of the film firmly. The superconducting nanodiamond heterostructures form qubits which can lead to the development of quantum computers provided the effect of disorder present in these structure can be firmly understood. Presently we concentrate on electrical transport properties of heavily boron–doped nanocrystalline diamond films around the superconducting transition temperature measured as a function of magnetic fields and the applied bias current. Microstructure of these films is described by a two dimensional superlattice system which can also contain paramagnetic impurities. We report observation of anomalous negative Hall resistance in these films close to the superconductor-insulator-normal phase transition in the resistance versus temperature plots at low bias currents at zero and low magnetic field. The negative Hall effect is found to be suppressed as the bias current increase. Magnetoresistance study shows a distinct peak at zero field when measured in the low current regimes which suggest a superconductor-insulator-superconductor structure of films. Current vs. voltage characteristics show signature of π-Josephson like behaviour which can give rise to a characteristic frequency of several hundred of gigahertz. Signature of spin flipping also shows novel spintronic device applications.

Proceedings Article | 3 February 2017 Paper

Nanomanipulation device fabrication: multilayerd graphene and OFET devices

C. Coleman, S. Khorasani, S. Ncube, D. Mtsuko, C. Botha, C. Sandrock, M. Fernandes, D. Levendis, S. Bhattacharyya

Proceedings Volume 10036, 1003608 (2017) https://doi.org/10.1117/12.2245446

KEYWORDS: Graphene, Nanomanipulation, Multilayers, Carbon, Field effect transistors, Crystals, Fabrication, Electrodes, Waveguides, Resistance

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We utilize nano-manipulting probes for the fabrication of a range of devices including multilayered graphene coplanar waveguides, suspended multilayered graphene hall bars and air-gap single crystal organic field effect transistors. We find that devices fabricated using this technique are of high quality and can be used to probe not only application based phenomena (such as transistor behaviour), but also fundamental quantum transport properties. Magnetoresistance measurements show that the multilayered graphene devices exhibit either quantum linear magnetoresistance (QLMR) or Shubnikov de-Haas oscillations depending on the topology (i.e. either wrinkled or smooth) of the graphene sheet. From this data we calculate the carrier density (ns) in the wrinkled graphene to be in the range 5.2 × 10⁹ cm^-2 (at B~0) to 3.5 × 10¹³ cm^-2 (at B=12 T) with effective masses of 0.001m_e and 0.121m_e, respectively. The smooth multilayer graphene devices have a carrier density 1.39 - 2.85 × 10¹² cm^-2 and effective mass (0.022m_e ≤ m*≤ 0.032m_e) as calculated from the analysis of the Shubnokov de-Haas oscillations. The high frequecny coplanar waveguide devices fabricated using this technique demonstrated high transmission up to 50 GHz, highlighting the potential for HF application. Organic field effect transistors were also fabricated using the manipulation technique, the transfere characteristics were measured, it was found that the devcies with channel length of 1 μm have non-linear transfere characterisitcs and pass a maximum current of between 0.1 and 10 nA. These OFET devices showed pronounced switching behaviour with mobilities of up to 3 cm²V^-1s^-1 in the best devices.

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