Polycyclic aromatic hydrocarbons: exploring new processes and materials for electronics
Baltazar, Jose A.
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Graphene is a two-dimensional sp2 hybridized carbon lattice that is also the fundamental building block of graphite. Graphene has attracted significant interest recently due to its distinctive electrical, optical and mechanical properties. These properties have spurred research directed at modifying graphene for use in a variety of electronic, optoelectronic, and sensor technologies. However, before graphene can be used in products, it is necessary to find methods to tune, modify, grow and integrate graphene features while substantially boosting device performance and maintaining current processing compatibility and ease of integration with existing manufacturing infrastructure. This dissertation focuses on developing techniques for controllably doping the graphene layer through scalable, industry friendly and simple chemical doping; using self-assembled monolayer compounds, photo-acid and photo-base generators, polymers and metal-organic species. We have, in fact, demonstrated simple p-n junctions fabricated in this manner. Characteristic I-V curves indicate the superposition of two separate Dirac points from the p and n regions, confirming an energy separation of neutrality points within the complementary regions; Raman studies of these methods have shown that these processes result in extremely low defect levels in the graphene. Our simple methods for producing patterned doping profiles in graphene films and devices open up a variety of new possibilities for forming complex doping profiles in a simple manner in graphene. This work can enable rapid testing, such as controlled work function tuning, complex doping profiles and simple post-fabrication tuning, of concepts for graphene that may be useful in both interconnect and transparent conductor applications. In addition to graphene doping, we also investigated approaches to the synthesis of few-layer graphene flakes, since current techniques still produce inferior materials. Exfoliation of Graphene Sheets by an Electron Donor Surfactant was demonstrated to generate few-layers graphene flakes that rival the electrical quality of reduce graphene-oxide (rGO) flakes. Last but not least, Diels-Alder adducts on silica were explored as a controllable carbon precursor for pristine graphene; these allow for a rational direct-growth-of-graphene-on-surface reaction mediated by copper catalyst, without the use of flammable precursors, such as methane, that are used in current methods of chemical vapor deposition synthesis of graphene.