Electrical Properties of Modified Graphene and Carbon Nanotube Devices

Graphene and carbon nanotubes are the two-dimensional and one-dimensional forms of carbon allotropes, respectively, and have been ideal materials for scientific and technological exploration due to their ultra small size and extraordinary physical properties such as high carrier mobility, large thermal conductivity and strong tensile strength. In this thesis, I focus on modifying the properties of graphene and carbon nanotubes, via chemical functionalization, strain, or encapsulation, so that they are better suited for applications. To create a band gap in the otherwise gapless spectrum of graphene, one common route is chemical functionalization. However, most functionalization methods are invasive and result in degradation in graphene's quality. In contrast, our chemically functionalized graphene using organometallic chemistry behaves as semiconductors with improved on / off ratios, while retaining high mobility. Application of strain in graphene is another route to tailor transport properties. We developed devices based on nano-electromechanical system (NEMS), which allows us to apply in situ strain in suspended graphene. Changes in contact resistance and mobility have been observed in single- and bi-layer graphene devices. Apart from graphene, we also focus on carbon nanotube devices. We developed techniques to fabricate carbon nanotube devices encapsulated in hexagonal boron nitride (hBN) with zero-dimensional ohmic contacts. These devices can carry high current density, and Coulomb blockade diamonds with excited state have been observed. Lastly, we explored a device geometry that combines both graphene and carbon nanotubes, with the goal of studying momentum-conserved tunneling between 1D and 2D systems. We developed techniques to fabricate suspended devices with dual gates, which allow us to observe interesting quantum transport features arising from both portions of graphene and carbon nanotubes. We also proposed hBN-based devices for future studies