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33. Solution processed self-assembly for aligned carbon nanotube devices

Author

Dear, John W.

Subjects
620.115
Abstract

One-dimensional nanomaterials have many useful properties for the development of future electronic devices. Single walled carbon nanotubes (SWCNTs) and nanowires (NW) exhibit excellent charge carrier transport characteristics and are efficient for electronic conduction as both semiconductors and conductors in thin films. With this change of materials comes an opportunity to also change device production techniques. Printing offers a fast and easy method for the deposition of materials for electronics, but printing systems require solutions of materials to act as inks. One of the main barriers to using carbon nanotubes (CNTs) in the field of printed electronics is the problem of creating reproducible films due to the poor dispersion in typical solution deposited CNT films. This random orientation of CNT within the film leads to a loss of charge carrier mobility as it is difficult to produce a conjugated path between electrodes and so charge carriers have to 'jump' the gap between neighbouring tubes. Two routes have been investigated as a part of this project to solve these problems. Firstly, composite films of CNT and polymerisable conjugated liquid crystals (LC) have been fabricated, which use the self assembly and crosslinking properties of the LC to create an aligned array of CNT in a semiconducting polymer. This is the first time this route to aligned, patterned composite semiconducting films has been performed and we have shown that this method provides an increase in conductivity and mobility of three orders of magnitude over a pure LC or CNT film. The fabrication of semiconducting field effect transistor devices has been achieved for the first time with such a composite system with the result of mobility increases of three orders of magnitude and a 60 % increase in the reliability of the device fabrication process over unaligned SWCNT films. Secondly, a functionalisation/ defunctionalisation system has been developed for SWCNTs to allow the effective solution deposition of thin films of CNTs while being able to recover the original electronic properties of the tubes. This defunctionalisation process adds an octadecylamine functional group for solubilisation and then uses a 200 C anneal process to remove the group after thin film deposition. The use of this process creates a decrease of five orders of magnitude in the sheet resistance between un-annealed and annealed films. Evidence is also presented to show that the defunctionalisation process has an effect on the number of defects on the SWCNT walls. Finally, potential mechanisms for this process are discussed. The process developed in this work takes places at far lower temperature, pressure and less caustic chemical conditions that any previously reported system for the removal of functional groups and healing of defects in CNT.

Published
2013

50. Experimental methodology for the measurement of plasticity on metals at high strain-rates

Author

Sancho Alexander, Cox Mike J., Aldrich-Smith Giles, Cartwright Tim, Davies Catrin M., Hooper Paul A., and Dear John P.

Subjects
Physics, QC1-999
Abstract

An experimental methodology has been developed for the tensile characterisation of ductile isotropic metals at high strain-rate. This study includes the region beyond plastic instability or necking, which is rarely analysed for conventional applications. The research explores an imaging technique used to track the geometry of the specimen during tensile tests and calculate true local values of stress and strain by applying Bridgman theory [1]. To improve the quality of the images taken at high strain-rate an in-situ high speed shadowgraph technique has been developed, and to obtain better results from the images a sub-pixel accuracy edge detection algorithm has been implemented. The technique has been applied to an austenitic stainless steel. Its tensile behaviour has been assessed by testing round samples at strain-rates ranging from quasi-static to ~103 s-1. The results obtained with the proposed methodology have been validated by comparison with more conventional techniques such as video-extensometer and digital image correlation in the pre-necking region and good performance even at the highest strain-rate tested has been proved.

Published
2018
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