UC Riverside

Graphene is a newly discovered material. It has many excellent properties, which make the research of this new material very important not only for the fundamental physics but also for the application. This thesis is a summary of our study in the electrical and thermoelectrical transport properties of graphene. In the first part of our work, we use a layer of molecules act as the charge reservoir to control the charge environment near or on graphene, we first obtained a mobility enhancement. By set the charge back and forth between graphene and the molecules, we found the graphene mobility can be widely tuned from 4000 to 19000 cm2/Vs. This strongly supports that charge impurities scattering is the main mechanism for graphene mobility. In addition, the charge neutral point in graphene can also be tuned independently over a wide gate voltage. A large memory effect is also found in the graphene device addressed with molecules, which makes this system potentially important for graphene application, such as graphene FLASH memory. In the second part of our work, we studied the thermopower of graphene with a wide range of mobility, i. e. varying degree of disorders, along with electrical conductivity at different temperatures. We have proved that the transport properties in graphene are indeed caused by the Dirac fermions particles. Moreover, we have found that the Mott relation fails in the vicinity of the Dirac point in high-mobility graphene. By properly taking account of high-temperature effects, we have obtained good agreement between the Boltzmann transport theory and our experimental data. In low-mobility graphene where the charged impurities induce relatively high residual carrier density, the Mott relation holds at all gate voltages.