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This work focuses on dielectric materials in organic thin film transistors. Silicon oxides whose surfaces are modified with hexamethyldisilazane (HMDS) and octyltriethoxyl Silane (OTS) are investigated. Organic semiconducting materials are used in the transistors made within the scope of this work. Although the devices made using our procedures did not exhibit satisfactory performance, we explored and understood some chemical and engineering aspects of the relevant dielectric/semiconductor interfaces in organic thin film transistors. Understanding these systems would help with improvements of the electrical properties and performance of such systems when plastic substrates are used at the next stage of the project.

A recent surface energy estimation method [1] interpreting contact angle hysteresis measurements was used to estimate surface energy of various commercially important polymer films including UV radiation cross-linked acrylic based monomer systems. The validity of the method was tested on highly hydrophobic non-polar amorphous fluoro-polymers using a number of polar and low surface tension liquids. Contact angle hysteresis was present on these surfaces even though surface morphology of the solution processed fluoro-polymers is close to ideal. Estimated surface energies using such probe liquids were consistent varying slightly with the probe liquid type. On such highly ordered and non-polar polymer surfaces use of polar and low surface tension liquids results in accurate surface energy estimation. However, use of polar probe liquids commonly employed in surface energy estimation methods, such as, Harmonic mean (HM), Geometric mean (GM) or Lewis Acid-Base method (LWAB) on polar surfaces such as polyester resulted in inconsistent surface energy values. To strengthen this observation, the ASTM surface energy estimation procedure (ASTM D2578 04a) developed for polyethylene and polypropylene surfaces (both non-polar) was employed on a sample polar polyester surface using the ASTM probe liquids. Results showed inconsistent surface energy values supporting the conclusion that care must be exercised during use of polar probe liquids in estimating surface energy on polar polymers with the contact angle hysteresis method. Finally, UV radiation cross-linkable acrylic polymer surface energies were estimated with the hysteresis method. Surface energy results were consistent based on five different probe liquids. It was observed that surface energy of the cross-linked monomer networks decreased slightly with increasing UV curing time.

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