第一章_石墨烯材料.ppt

As with many other quantum phenomena, the observation of the QHE usually requires low temperatures,typically below the boiling point of liquid helium (1). Efforts to extend the QHE temperature range by, for example, using semiconductors with small effective masses of charge carriers have so far failed to reach temperatures above 30 K。We show that in graphene, a single layer of carbon atoms tightly packed in a honeycomb crystal lat- tice, the QHE can be observed even at room temperature. This is due to the highly unusual nature of charge carriers in graphene, which behave as massless relativistic particles (Dirac fermions) and move with little scattering under ambient conditions The definitive evidence that the carbon sheets obtained by this method are only a single atomic layer thick was obtained with atomic force microscopy (AFM). Multiple cross-sections were recorded of the sample laid onto a mica substrate, and the step heights measured between the surface of the sheets and the substrate were consistently found to be 4 Angstrom, proving them to be only a single atom thick. Electron diffraction was used to verify that the carbon sheets are crystalline graphene. 由于石墨烯氧化物存在大量的含氧官能团, 从 而表现为亲水性, 可以高度分散在水溶液或其他有 机溶剂中, 利用还原去氧反应或简单加热处理能够 [42,48~50] 将其转变成石墨烯 (图５). 由于石墨烯氧化物可以通过氧化石墨材料的过程大量、高效地制备, 因此石墨烯氧化物是大规模制备石墨烯材料的另一条有效途径. 另一方面, 溶液分散的石墨烯氧化物可以 和聚合物等其他材料相混合并形成复合材料体系, 表现出优异的力学和电学性能。 Fig. 3a,b shows what appear to be a graphene monolayer and a graphene bilayer, respectively. Figure 3b is particularly interesting as the right side of the ?ake consists of at least two layers, whereas on the left side, a single monolayer protrudes.Figure 3c shows the normal-incidence electron diffraction pattern of the ?ake in Fig. 3a. This pattern shows the typical sixfold symmetry expected for graphite/graphene.Figure 3d,e shows normal-incidence selected-area diffraction patterns for the ?ake in Fig. 3b, taken with beam positions close to the black and white dots, respectively. This me