Synthesis, Characterization, and Selected Properties of Graphene

Abstract

Carbon nanotubes (CNTs) and graphene are two of the most studied materials today. Two-dimensional graphene has specially attracted a lot of attention because of its unique electrical properties such as very high carriermobility [1–4], the quantum Hall effect at room temperature [2, 5], and ambipolar electric field effect along with ballistic conduction of charge carriers [1]. Some other properties of graphene that are equally interesting include its unexpectedly high absorption of white light [6], high elasticity [7], unusual magnetic properties [8, 9], high surface area [10], gas adsorption [11], and charge-transfer interactions with molecules [12, 13]. We discuss some of these aspects in this chapter. While graphene normally refers to a single layer of sp2 bonded carbon atoms, there are important investigations on biand few-layered graphenes (FGs) as well. In the very first experimental study on graphene by Novoselov et al. [1, 2] in 2004, graphene was prepared by micromechanical cleavage from graphite flakes. Since then, there has been much progress in the synthesis of graphene and a number of methods have been devised to prepare high-quality single-layer graphenes (SLGs) and FGs, some of which are described in this chapter. Characterization of graphene forms an important part of graphene research and involves measurements based on various microscopic and spectroscopic techniques. Characterization involves determination of the number of layers and the purity of sample in terms of absence or presence of defects. Optical contrast of graphene layers on different substrates is the most simple and effective method for the identification of the number of layers. This method is based on the contrast arising from the interference of the reflected light beams at the air-to-graphene, graphene-to-dielectric, and (in the case of thin dielectric films) dielectric-to-substrate interfaces [14]. SLG, bilayer-, and multiple-layer graphenes (<10 layers) on Si substrate with a 285 nm SiO2 are differentiated using contrast spectra, generated from the reflection light of a white-light source (Figure 1.1a) [15]. A total color difference (TCD) method, based on a combination of the reflection spectrum calculation and the International Commission on Illumination (CIE) color space