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Title: Nanostructured Molecular Electronic Devices
Author: Barlow, Iain J.
ISNI:       0000 0001 3445 4877
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2007
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Candidate organic semiconductor materials based on a,ro-dihexylquaterthiophene (dH4T) and a,ro-dihexylbis(phenylene)bithiophene (dHPTTP) core systems were synthesised. The tenninal positions of the alkyl substituents were substituted with, thioacetate, phosphonic acid, glycolic ester and allyl ether groups to enable the fonnation of self-assembled monolayers (SAMs) of the adsorbates onto Au, Ah03 and H-Si surfaces. These were then probed with x-ray photoelectron spectroscopy (XPS) and friction force microscopy (FFM). Analysis of the XPS spectra confirmed that the oligomers fonned monolayer films onto the respective substrates although the allyl-terminated oligomers were subject to oxidation when attached onto H-Si by thermally-initiated radical attachment. Comparison of this method with photochemical initiation highlighted a potentially competing photolysis reaction. FFM showed that the frictional properties of both the thiolate and phosphonic acid SAMs on Au and Ah03 for the oligomers depended on both the tail group polarity and the density of packing for the adsorbates, whilst the allyl-capped materials formed disordered monolayers on H-Si. Chemical patterns of the thioacetate and phosphonic acid-terminated oligomers were produced by the irradiation of methyl-tenninated alkanethiols and alkylphosphonic acids with 244 nm UV light. The irradiation and subsequent displacement of the exposed adsorbates with the dH4T and dHPTTP-based thioactetates and phosphonic acids resulted in areas of relatively high and low friction, which was imaged by FFM. The SAM photomodification process on Ah03 was monitored by XPS, and suggested C-P bond photolysis as a potential mechanism. Scanning near-field photolithography (SNP) was then used to generate dH4T and dHPTTP features into alkanethiol and phosphonate SAMs. The smallest features, of 40 nm fwhm demonstrate that SNP is a viable method for the preparation of organic semiconductors with nanometre resolution, with potential application in the production of self-assembled monolayer field-effect transistors (SAMFETs).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available