Electronic transport and mechanical resonance modes in graphene

Graphene is a two-dimensional sheet of carbon atoms arranged in a hexagonal honeycomb lattice. After the first electronic devices made from single layer graphene were demonstrated in 2004, a tremendous interest has arisen around it. It is driven by the unique properties of graphene: it has a linear band structure so that the charge carriers behave like massless relativistic particles and very few materials can rival its mechanical, electronic, and optical properties, and most remarkably they all exist in a single substance. Consequently, graphene has been envisioned to either replace many currently used materials, or to enable conceptually new applications. Various aspects of graphene physics and devices has been studied in this Thesis. Transport experiments were performed on high quality suspended graphene samples, where the intrinsic performance limits can be probed. At millikelvin temperatures, the ballistic conductance in monolayer graphene manifests in electron wave interference reminiscent of Fabry-Pérot resonances in optical cavities. These interference patterns were analyzed to reveal therenormalization of Fermi velocity in graphene at low charge densities. At high bias voltage regime, shot noise thermometry was employed to study the electron-phonon scattering mechanisms. In suspended monolayer graphene, hot electron relaxation was found to be dominated by two-phonon scattering from thermally excited ripples, whereas in bilayer graphene the intrinsic optical phonons played the dominant role. Graphene is the ultimate material for nonlinear, tunable two-dimensional nanoelectromechanical systems. In this Thesis, methods to fabricate and measure graphene mechanical resonators were developed. In addition, diamond-like carbon resonators were studied, which may be a promising alternative for applications utilizing multilayer graphene membranes.