Panchal, Vishal

Epitaxial graphene (EG) on SiC is readily compatible with CMOS processes and holds great potential for wafer scale production of devices. My aim is to understand the electronic properties of EG using bulk transport and nanoscale mapping techniques.It is shown that miniaturisation of single-layer graphene (1LG) devices even down to 100 nm does not significantly change the superior electronic properties of the material. However, unoptimised device geometry results in an increase of 1/f noise, significantly affecting the magnetic field sensitivity of devices. Detection of small magnetic moment reveals that EG devices still outperform conventional semiconductor devices.To study the nanoscale properties of EG, a comparison of amplitude- and frequency-modulated Kelvin probe force microscopy and electrostatic force spectroscopy is carried out. The most accurate of these techniques are used for non-contact measurements of the various properties of EG. In addition, the local electrical and magnetic gating effects are also investigated using scanning gate microscopy (SGM). Work function measurements reveal that patches of double-layer graphene (2LG) exhibit a significantly higher carrier density, affecting the conductivity and sensitivity of devices. Furthermore, electric field screening is measured in 2LG devices using SGM. A carrier inversion is observed at lithographically defined edges of devices, which could be further enhanced with lateral gates. Resists and chemicals used throughout the fabrication process are shown to affect the carrier type in the most extreme cases and was used to create a unique planar p-n junction. Changes in the ambient air can lead to further doping effects, which are reversed in vacuum.Novelty of this work is in the combination of bulk transport and local nanoscale work function mapping techniques, which led to a deeper understanding of the unique electronic properties of EG

Epitaxial graphene nanodevices and their applications for electronic and magnetic sensing

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Royal Holloway - Pure