The Study Of Weak Localization Effect And Disorder Induced Anomalous Quantum Phenomenon In Graphene System

Graphene has been featured as an ideal two dimensional mesoscopic transportation system, in which quantum interference of electron and disorders are very important. Weak localization directly results from the electron phase interference, therefore, we study the interference properties of Dirac electron in graphene and discuss the function of disorder via weak localization effect in this thesis.The first work is as follows, we obtain graphene sheet by the well established exfoliation approach. A standard lift-off process fabricated the4-probe electrodes using the50nm-thick Au film. We observe the increase of the dephasing lengths of the graphene sheet after the deposition of Pd nanoclusters, as demonstrated by the measurement of weak localizations. The counterintuitive experimental result is the first time to be reported. At the same time, the dephasing lengths are found to reach some saturated values with the decreasing temperatures, essentially the zero-temperature decoherence (ZTD). Detailed analysis shows that our data agree well with the predication of Golubev and Zaikin mechanism. We hold the viewpoint that the absorption of the Pd clusters introduces both additional scattering and charge transfer to the graphene sheet. The scattering suppresses the quantum coherence, while the additional charge smoothes the local electric field fluctuation. Such smoothing suppresses the ZTD and thus increases the upper bound of the saturated dephasing lengths of Dirac Fermions in graphene. The final improvement is the result of the competition between the scattering suppression and the charge transfer smoothing effect.The second work shows below, our graphene samples are growning on copper foils with solid carbon source method. The as-grown graphene films are transfer to Si substrate covered a300nm thickness of SiO2with a typical PMMA-assisted process. Under the evidence of the microscope photograph, the Raman spectrum and the measurement of conductivity, we may draw a conclusion that the grown graphene is single layer, consistent and macroscopic uniform. After point conductive silver glue onto graphene as electrodes, we start the measurement with perpendicular magnetic field. We observe the prominent room temperature weak localization effect, which, to the best knowledge of the writer, is the first time ever to be reported. Though the microscope photograph, Raman spectrum, Resistence-temperature curve and mobility, we conclude that our graphene sample contains a large amount of disorders. Futher analysis shows that because of these disorders we can observe the room temperature weak localization effect.