The Weak Localization Study Of Bilayer Graphene Decorated By Ag Clusters

Novoselov and his collaborators have isolated monolayer graphene using mechanical exfoliation in 2004. The most interesting aspect of monolayer graphene is its Dirac cone structure in energy band, which has a linear dispersion at low energy, and the effective mass of charge carriers is nearly zero. There are two unequivalent Dirac cones in energy dispersion relation, which can be regarded as pseudospin. The projected pseudospin along the direction of momentum is a good quantum number, leading to the chirality of charge carriers and a Berry phase of π The Berry phase determines the weak antilocalization in the low magnetic fields. The ultrathin atomic scale space confinement, anomalous geometry phase and relativity-like transportation make monolayer graphene an unique experimental platform for studying 2-dimensional coherent electronic transport. However, the electronic transports in bilayer is distinctly different from the monolayer graphene. The dispersion relation at low energy is parabolic, the effective mass of quasiparticles is not zero, and the Berry phase of charge carriers during transportation is 2π This leads to the result that bilayer graphene show weak localization in low magnetic fields. The evolution of layer-number dependent transport and the modification of the traditional 2D transport physics in this new platform is becoming the frontier of present electronic transport research.Graphene has an open structure. It can be decorated using various of deposited impurities. This article is based on the previous research of our group. Using cluster beam method, we deposit clusters on bilayer graphene (our work only concerns bilayer graphene) and measure the transport properties after cluster deposition. We have obtained the bilayer graphene flakes by the mechanical exfoliation method. A standard lift-off technique is used to fabricate 4-probe Au electrodes. Raman spectroscopy determines the thickness of graphene. We deposit Ag clusters on bilayer graphene, measure the magnetoconductance and compares it with the data before deposition. We analyze the experimental data using standard bilayer graphene weak localization formula. Fitting the data by this standard formula, we obtain the phase coherence length which is found to saturates at low temperatures. We propose that there are a large number of disorder in graphene, which will generate some electro-magnetic fluctuations in graphene and causes electronic dephasing at low temperatures. We also notice that the phase coherence length is increased after Ag cluster deposition. Through careful analysis, we propose that Ag clusters deposition will not only cause the additional scattering for charge carriers but also p-type doping. The electrons transfer from bilayer graphene to Ag clusters, which will smooth the electro-magnetic fluctuations in the system, and enhance the upper limit of phase coherence length. The final experimental result is the competition between additional scattering and the smoothing of electro-magnetic fluctuations. Our data agrees well with the prediction of Golubev-Zaikin mechanism for a 2D disorder electron system.