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Title: Solution processable carbon-based electronics
Author: Ball, James Michael
ISNI:       0000 0004 2699 1375
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Fabricating electronic devices using solution-based processing methods opens up a broad range of potential applications that are inaccessible to conventional semiconductor fabrication technologies. The chemically diverse family of carbon-based materials are suitable for this purpose with almost limitless possibilities for molecular tailoring. The present work is a study of some of the materials for and device physics of field-effect transistors based on solution processable layers. Each aspect of this work is chosen to address a current difficulty in the development solution-processable carbon-based electronics. For portable and battery-powered applications, low-power circuits are required. This can be achieved by using a complementary logic circuit architecture (that requires both electron and hole transporting semiconductors) where the discrete devices operate at low voltages. Practically, this requires a high capacitance gate dielectric which is compatible with solution processing of a range of semiconductor materials. One family of molecules suitable for this purpose are self-assembling phosphonic acids that can form molecular monolayers. In the present study, molecular tailoring of this family of molecules is investigated as a route towards improving the compatibility of these dielectrics with solution processed semiconductors. One of the difficulties with utilising a complementary logic circuit architecture is the requirement of a suitable electron transporting semiconductor. This semiconductor must be solution-processable, exhibit a high electron mobility and be stable against degradation upon atmospheric exposure. Although many p-channel semiconductors fulfil these requirements, equivalent performance in many families of n-channel semiconductors remains challenging. In the present study, the use of fullerenes, a widely used family of semiconductors, is explored for implementation as an n-channel material in field-effect transistors. Their electronic structure is controlled by chemical tailoring of each molecule and the impact of this parameter variation on the air-stability of these fullerenes is assessed. Graphene, potentially one of the most important materials for future electronics, is currently impractical to prepare over large areas. Chemical derivation routes are sought which allow processing of graphene from solution. One of the most important routes is solution phase exfoliation of graphene oxide followed by thermal or chemical reduction. Unfortunately this introduces a high density of defects within the final graphene layer which ultimately limits the charge-carrier mobility. Here, a milder oxidation with surfactant-assisted solution phase exfoliation is investigated as a route to improving the quality of graphene films following reduction. The electronic properties of thin- films of these chemically-derived graphene layers are explored as the active layer in field-effect transistors.
Supervisor: Anthopoulos, Thomas ; Bradley, Donal Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral