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Title: An indole trimer : synthesis, self-assembly and applications
Author: Coe, Iris K.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2013
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The organic semiconductor, the indole -5- carboxylic acid asymmetric trimer (ICAT), was chemically synthesised using a new procedure. Self- assembly of ICAT in solution, produced narrowly dispersed discotic nanoparticles that are stable in solution and transferable between surfaces. Highly ordered ICAT bulk molecular and nanoparticle thin films were produced through controlled assembly of ICAT at the solution /solid interface, using glass substrates functionalised with a variety of self assembled monolayers (SAMs). Two films, in particular, on the hydroxyl and the amine -functionalised substrates had extremely well ordered microstructures, suitable for device application. An immersion based deposition technique was developed, where gold and SAM - functionalised glass substrates were immersed in ICAT solutions made with solvents with a range of polarities. At short immersion times, bulk or particulate films were deposited, as a function of immersion solvent. Longer immersion times produced size tailored vertically aligned nanorod and nanowire arrays, as a function of immersion solvent. The immersion time also controlled both the rod density and rod orientation on the substrates. The results were interpreted in terms of heterogeneous nucleation and subsequent growth. Solvophobic forces induced homogeneous nucleation rather than heterogeneous nucleation, in the immersion systems with water and hydrocarbon based immersion solvents. Aligned nanorods and nanowires were assembled on gold and hydroxyl -functionalised glass substrates when polar aprotic immersion solvents were used. There was no obvious correlation between nanostructure dimensions and solvent polarity in these experiments. This is the first time vertically aligned nanorod arrays have been fabricated with small organic functional molecules, through a solution based technique (non -template). Solution based deposition techniques developed here were used to deposit ICAT onto field effect transistors (FETs), resulting in devices with a range of ICAT film morphologies. Single crystal devices were also produced where the ICAT crystal bridged the active channel, defined as the gap between the source and drain electrodes. Several chips, with over 20 FETs on each chip, with each ICAT film morphology type, were fabricated. Selected chips had consistent, reproducible current/voltage (IV) outputs that varied within « one order of magnitude, when probed on all areas. The devices produced n and p -type unipolar activity and the onset of ambipolar activity in ambient conditions, at low voltage probing ranges. Carrier type was dependent on the film morphology. Device lifetime was dependent on film thickness.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available