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Title: Comprehensive study of large-area CVD graphene field effect structures at DC and microwave frequencies
Author: Adabi, Mohammad
ISNI:       0000 0004 6348 2393
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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Following the successful isolation of graphene in 2004 by Novoselov and Geim, a significant amount of time and energy have been invested in studying the properties of this 2D material. Many researchers and companies from all around the world have established the vision of incorporating graphene into industrial scale applications where full utilisation of this material can be achieved outside the laboratories. One of the major technical challenges facing electrical characterisation of graphene is the different processes such as lithography and plasma etching that this material has to be exposed to before an electrical measurement can be conducted on it. These processes are known to partially deteriorate the inherent properties of graphene. A potential solution is to employ a contact-free electrical measurement technique where transport properties of large-area graphene films can be extracted without the need for realization of contacts to the surface of graphene. This thesis explores a microwave resonance technique to study the field effect properties of graphene based field effect structures. Field effect devices with a variety of dielectric films are fabricated and performance of each of them is analysed separately. This microwave method will prove to be consistent with the DC measurements and also in perfect agreement with the theoretical results from the Boltzmann equation. Further to successful demonstration of the microwave cavity technique, a novel stacked heterostructure of graphene-aluminum nitride-graphene is designed and developed. It will be shown that the sheet resistance of one graphene layer in such structure can be modulated by the application of a gate voltage to another graphene layer. This system resembles a parallel circuit of the two graphene films where each layer has a distinct doping level. The Boltzmann’s framework is used and the obtained microwave field effect conductivity result are accompanied by a fitting model. Switching ratio of as high as 4.5 is achieved at room temperature by controlling the doping level in each graphene sheet. This heterostructure system presents a promising new device structure that can potentially be used as a dual-biosensing device for biomedical applications. Such device could utilise the piezoelectric properties of aluminium nitride in combination with the strength, conductivity, transparency, and bio-compatibility of graphene to detect and measure the mass as well as the charge of various cells including the cancer cells. The dual-sensing mode is expected to significantly improve the false negatives that are currently obtained via other cell capturing methods.
Supervisor: Klein, Norbert ; Heutz, Sandrine Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available