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Functionalisation of carbon nanotubes for molecular electronics

Carbon nanotubes (CNTs) have been chemically functionalised for electronic device applications using plasma exposure processes. Two areas of CNT device have been investigated. Firstly the conversion of the inherent p=type field effect behaviour of the CNTs to n-type field effects behaviour and secondly to control the positioning of CNTs on a substrate. To convert CNTs from p-type to n-type semiconductors, the chemically unreactive CNTs have been functionalised by exposure to fluorinated plasmas, both CF<sub>4</sub> and SF<sub>6</sub>. Further functionalisation with 1,2-diaminoethane was then employed on functionalised CNTs exposed to a CF<sub>4</sub> plasma at low bias conditions, the purpose of the amine molecule is to donate electrons to the CNTs. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy have confirmed both the presence of fluorine and nitrogen on the CNT surface as well as the structural integrity of the CNTs. The functionalisation mechanism was seen to depend on the ionic current density and the fluorine plasma during the initial fluorine exposure stages. Electronic characterisation of the plasma fluorinated and the 1,2-diaminoethane functionalised CNTs in backgated geometry was then applied with randomly distributed CNTs on gold electrodes. The fluorinated CNTs have exhibited p-type field dependent behaviour in air, whilst the aminated CNTs have begun to show indication of n-type field dependent behaviour. The second process used molecular stamping of 2-thiolpyridine using poly(dimethylsiloxane) (PDMS) stamps; a method which allows applications for both pristine and functionalised CNTs. Molecular stamping of 2-thiolpyridine using poly(dimethylsiloxane) (PDMS) stamping techniques, have been developed to self-assemble CNTs over a substrate and onto predefined electrode structures. By optimising the concentration of 2-thiolpyridine in ethanol and using a dilute suspension of CNTs in 1,2-dichloroethane, CNTs could be self-assembled using two similar fabrication processes. The molecular stamping experiments have confirmed that altering the order of the steps within the fabrication process, to have CNTs on top of electrodes or underneath electrodes, can control the field dependent qualities of devices in a limited gate voltage range. The limiting factor to device reproducibility is the ability to produce homogeneous CNT solutions. With control over the CNT chirality and suspension it is predicted the molecular stamping methods would be a fast and reliable process for high yield CNT devices.
Date January 2005
CreatorsPlank, Natalie O. V.
PublisherUniversity of Edinburgh
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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