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Title: Nanopatterning and nanoscale characterisation of solution-processible electronics
Author: Shaw, Joseph
ISNI:       0000 0004 5349 5510
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Solution-processible electronics represent an emerging technology that will revolutionise the field of inexpensive large-area/volume electronics. In this thesis two scanning probe-based methods; scanning thermal lithography (SThL) and conductive atomic force microscopy (CAFM), are used to firstly enhance the patterning resolution of organic semiconductors and secondly improve the electrical characterisation techniques used to study charge transport in solution-processed systems. By combining SThL with suitable organic precursors, on-demand patterning of semiconducting pentacene nanoribbons ~73 nm in width, is demonstrated. By using pentacene nanoribbons as the transistor semiconductor, the first fully functional nanostructured organic transistors via SThL were produced. Using finite element simulations and experimental data, the effects of simultaneously heating the substrate during SThL patterning were assessed. Substrate heating was found to be an economical and simple way to increase SThL 'writing' speed, and hence patterning throughput by ~2,000%. To demonstrate the applicability of SThL beyond direct patterning of electro-active compounds, an organic precursor was used as a positive etch mask for the patterning of various metal films. This approach enabled the patterning of metal electrodes with sub-500 nm resolution highlighting the potential of SThL as a rapid prototyping tool for nanoscale electronics. Finally, the origin of the enhanced electrical conductivity observed in solution-processed transparent electrodes composed of silver nanowires (AgNWs) and a conductive binder was studied using CAFM. Two different solution-processible binder materials; reduced graphene oxide and zinc oxide (ZnO), were employed. By analysing the lateral charge transport in these composite electrode systems, the impact of the binder material on the macroscopic conductivity was assessed. The formation of binder-composed conductive bridges between AgNWs was identified as a key feature responsible for the enhanced conductivity in the composite electrodes. The ZnO-AgNW hybrid had sheet resistance comparable to conventional indium tin oxide electrodes, with the added benefit of low temperature (~200 °C) solution-processing.
Supervisor: Anthopoulos, Thomas; Stavrinou, Paul Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral