Chemical and Physical Graphene Modifications
Tour, James M.
Doctor of Philosophy
This dissertation is inspired by recent progress in the chemistry, physics, and nanotechnology of graphene, a single layer of carbon atoms. Studying and controllably modifying the electrical properties of graphene while minimizing damage to the lattice continues to be a challenge to the scientific community. Chapter 1 focuses on the covalent attachment of molecules with different functional groups to graphene and how functionalization modifies the electrical transport properties of graphene field effect transistors (FET) devices. Functionalization is shown to predominantly induce p-type doping, undiminished mobility, and increased conductivity at the neutrality point. Physisorbed molecules desorb easily and do not have a significant effect. Statistical analysis enables us to extract trends even though identically fabricated graphene devices can exhibit a wide range of electrical behaviors, emphasizing that conclusions should not be drawn based on singular extremes. In Chapter 2 we present the fabrication and characterization of graphene antidot lattices produced by placing graphene on pre-patterned substrates. While the graphene remains intact atop a periodic well pattern we observe a surface potential differential inside vs. outside the wells. Chapter 3 investigates graphene FETs with multiple neutrality points. We used Raman mapping to determine if multiple local gating fields can be spatially resolved. While we were able to show doping inhomogeneity in graphene devices, there was no obvious difference between devices with one vs. multiple neutrality points. In Chapter 4 we demonstrate a method to grow graphene from solid carbon sources. I confirmed the single layer nature of the produced graphene using atomic force microscopy (AFM) and fabricated and characterized intrinsic FETs based on solid-derived graphene. In Chapter 5 we propose that graphene layers nucleate along and underneath the edges of existing graphene layers with a continuous layer remaining on top. My AFM characterization of hexagonal graphene onions provided evidence for our proposed nucleation mechanism. Chapter 6 is a report on graphene resistor devices that were contributed to an experiment aboard the International Space Station which seeks to investigate the effects of radiation exposure. Overall, the work accomplished in this dissertation constitutes a step forward toward controllable device behavior in graphene based electronics.
Graphene; Carbon; Nanoscience; Nanotechnology