Electronic and Spintronic Properties of Graphene

In this thesis, I summarize our studies investigating the electronic properties and spintronic properties of transition metal doped graphene over the last six years. In chapter 2, I will be talking about the device fabrication steps including our graphene exfoliation, graphene identification, ebeam lithography steps and electrode metallization. The measurement setup, including our molecular epitaxy system (MBE) and AC lock-in measurement, will also be discussed in detail. To utilize graphene as an electronic base material, it is important to understand the interface between contact electrodes and graphene. Transition metals (TMs) have been widely used as a contact material for graphene devices but the charge transfer mechanism between TMs and graphene was not well understood. A specially designed MBE system was built to deposit TM atoms onto graphene devices and to measure the magnetotransport properties in situ. In chapter 3, I will be discussing our experimental studies on the charge transfer, scattering, and effects of cluster formation on graphene. These results are important for improving the performance of graphene electronic devices.For graphene spintronics, one of the most important questions is the spin relaxation mechanism in graphene. It is theoretically predicted to have a long spin lifetime of over 1 ms. However, spin lifetimes observed are only about 200 ps. The big difference between these two values is an important scientific question to address in order to achieve long spin diffusion length. In chapter 4, I utilized molecular beam epitaxial growth to systematically study the spin lifetime in graphene. It is demonstrated that Coulomb scattering (charged impurities) is not the dominant spin relaxation mechanism