Physics and Astronomy Masters Defense

Gaither Frye

Composition and Morphology of Conjugated Polymer Brush and Analogous Spuncast Films

Organic semiconductors possess properties for the development of low cost, highly tunable, and easy to fabricate electronic and photonic components that stand to surpass today’s silicon-based technology. One promising candidate as an active layer in organic electronics is conjugated polymer brushes (CPBs), but their intrinsic properties remain largely unknown. CPB synthesis is different from conventional polymer synthesis in that the molecules grow normal to their substrate surface. In contrast, conventional synthesis methods, such as spincasting, produce random, spaghetti-like distributions of polymer molecules. The vertical orientation in CPBs allows charge transport along molecular chains between top and bottom electrodes in electrode-polymer-electrode devices. However, transport parameters for CPBs cannot be compared with those for analogous spuncast films because the packing densities of the polymers in CPBs are not generally quantified. In this work, we quantitatively characterize the composition and morphology of poly(3-methylthiophene) (P3MT) CPBs and analogous poly(3-hexylthiophene) (P3HT) spuncast films using Rutherford backscattering spectrometry (RBS) and atomic force microscopy (AFM) techniques. Areal densities of each polymer are found using RBS as a function of thickness, measured by AFM scratch profilometry. Our results indicate that the volume densities of these polymers are thickness independent andare comparable to each other (P3MT = 3.6 ± 0.7 monomers/nm3 and P3HT = 3.6 ± 0.5 monomers/nm3). This result makes it possible to make comparisons about the source of increased charge transport in CPB films, but more work is needed to verify. In addition, the work also involved the further development of an in-situ motorized target wheel for RBS measurements using low-cost microcontroller components and modifying existing LabVIEW programs, in order to significantly enhance data acquisition for RBS experiments.

Committee: Dr. Frank Tsui, Dr. Art Champagne, Dr. Wei You

This defense will be held remotely via Zoom. Please see department listserv for details.