Mechanical and Electrical Properties of Graphene Sheets

This thesis examines the electrical and mechanical properties of graphene sheets. We perform low temperature electrical transport measurements on gated, quasi-2D graphite quantum dots. In devices with low contact resistances, we use longitudinal and Hall resistances to extract a carrier density of 2-6 x 10 11 holes per sheet and a mobility of 200-1900 cm 2 /V-s. In devices with high resistance contacts, we observe Coulomb blockade phenomena and infer the charging energies and capacitive couplings. These experiments demonstrate that electrons in mesoscopic graphite pieces are delocalized over nearly the whole graphite piece down to low temperatures. We also fabricate nanoelectromechanical systems (NEMS) from ultra thin graphite and graphene by mechanically exfoliating thin sheets over trenches in SiO 2. Vibrations with fundamental resonant frequencies in the MHz range are actuated either optically or electrically and detected optically by interferometry. We demonstrate room temperature charge sensitivities down to 2x10-3 e/Hz ½. The thinnest resonator consists of a single suspended layer of atoms and represents the ultimate limit of a two dimensional NEMS. In addition to work on doubly clamped beams and cantilevers, we also investigate the properties of resonating drumheads, which consist of graphene sealed microchambers containing a small volume of trapped gas. These experiments allow us to probe the membrane properties of single atomic layers of graphene. We show that these membranes are impermeable and can support pressure differences larger than one atmosphere. We use such pressure differences to tune the mechanical resonance frequency by ~100 MHz. This allows us to measure the mass and elastic constants of graphene membranes. We demonstrate that atomic layers of graphene have stiffness similar to bulk graphite (E ~ 1 TPa). These results show that single atomic sheets can be integrated with microfabricated structures to create a new class of atomic scale membrane-based devices. Colorado at Boulder. iv To my family v ACKNOWLEDGMENTS When I first arrived at Cornell University and joined Paul McEuen's lab, it was a lonely and empty place. Paul and his lab were still at Berkeley so the labs at Cornell were just empty rooms. I sat at my desk staring at freshly painted white walls and began to ponder whether I would survive the long years of a Ph.D. in such a dreary setting. Fortunately, things soon changed with the arrival of equipment and people that was to transform the corridors of Clark Hall to a lively and exciting …