Graphene：Properties and Devices.ppt

Xia, F.; Farmer, D. B.; Lin, Y.-m.; Avouris, P., Graphene Field-Effect Transistors with High On/Off Current Ratio and Large Transport Band Gap at Room Temperature. Nano Lett. 2010, 10 (2), 715-718. Electrical spin injection in normal metals is routinely achieved by contacting ferromagnets like Fe, Ni, and Co with normal metals such as Cu and Al, and driving a current through the system. In semiconductors, electrical spin injection is more challenging because of the resistance mismatch between the semiconductor and possible ferromagnetic metal contacts[Phys. Rev. B, 2000, 62, R4790.].Nevertheless, spin injection into a semiconductor is feasible from a conventional ferromagnet when the interface resistance between the semiconductor and the ferromagnet is sufficiently large. The effect was attributed to the nonvanishing overlap between the wave functions of the localized moments in the magnetic insulator and the itinerant electrons in the metal. (Proc. SPIE 2157, 285 (1994).) The electronic wave functions can be described by atomiclike wave functions at the surface of thin Al films. (Phys. Rev. B 17, 662 (1978).) The spatial range is similar for the atomic wave functions in Al and graphene, so we expect the overlap between the localized moments and itinerant electrons in graphene at EuO/graphene interfaces to induce exchange interactions comparable to those observed for EuO/Al. Based on the results reported in (Phys. Rev. B 38, 8823 (1988).), we roughly estimate that exchange splittings in graphene due to the ferromagnetic insulator EuO could be of the order of 5 meV. This will produce ef?cient spin injection by overcoming the conductance mismatch between the ferromagnetic (FM) metal electrodes and the SLG. Figure 1. Graphene nanoribbon in electric fields. Diagram of a zigzag graphene nanoribbon (ZGNR) with external transverse electric field Eext. Eext is applied across the ZGNR along the lateral direction (x direction) in an open-circuit split-gate configuration an