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Title: Perpendicular transport and electromechanical properties of graphitic composites and multilayers
Author: Taylor-Harrod, Isaac
ISNI:       0000 0004 7967 850X
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2019
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This thesis presents several milestones in the production of flexible electronics utilising quantum tunnelling between graphitic carbon. Two such materials are investigated. The first is a composite material consisting of conducting highly oriented pyrolytic graphite particles embedded in an insulated polydimethylsiloxane (PDMS) matrix. This is referred to as a graphite silicone composite (GSC). The second is a multilayer stack of two graphene electrodes with adsorbed organic molecules (naphthalene diimide-pyridine) between them forming a tunnelling barrier. The piezoresistive response of GSCs is analysed by applying calibrated stress steps and observing the resistance response of the composite over time. We then fit this response to a tunnelling percolation model, followed by the extraction of material parameters of viscoelastic creep time and tunnel barrier height using the fit. We also investigate the dependence of the piezoresistance of GSCs and similar composites on material parameters using this model. The flexible tunnelling percolation model allows for the effects of perturbations on composites to be predicted without the need to simulate the 3D locations of conducting particles. To avoid the limitations of GSCs such as viscoelastic delays, we develop a multilayer stack device. This allows us to study a single graphene/insulator/graphene junction in place of a statistical average over a percolation network. We use a new synthesis method utilising thermal deposition and self-release layer graphene transfer to create these devices. This allows for the adsorbed molecules to remain on the graphene and bind together. The IV curves of these devices are tested with varying gate voltage applied to the sample, using two different sample sizes and at 77 and 300 K. The samples demonstrate a tunnelling current that decreases with negative gate voltage and decreasing sample size. Samples at 77 K see higher tunnelling currents.
Supervisor: Takashina, Kei ; Nogaret, Alain Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available