ABSTRACT
Since the first mechanical isolation of graphene from graphite crystal in 2004 [3], intense efforts have been made to develop technologies for large-area graphene synthesis, including reduction of graphite oxide, thermal decomposition of SiC, and CVD of hydrocarbons on transition metals. In particular, graphene synthesized by CVD on Ni and Cu substrates has shown great promise owing to its large scale, high quality, and transferability to arbitrary substrates for various applications. On the other hand, epitaxial graphene on SiC is more convenient to be used for microelectronics. 4.2.1 Mechanical Exfoliation
The first isolated graphene was obtained by mechanical exfoliation of graphite in 2004 at the University of Manchester [3]. An adhesive tape (Scotch tape) is used to repeatedly stick and peel off graphite crystals into increasingly thinner pieces, which are then transferred on an oxidized Si substrate (300 nm SiO2) simply by a gentle press of the tape. The transferred graphene adds a tiny optical path to the Fabry-Perrot cavity created by the 300 nm SiO2 layer on Si. An optical contrast between graphene and the substrate is maximized at about 12% under a light with wavelength 550 nm, where the sensitivity of the human eye is optimal. Graphene becomes visible and can be easily identified under an ordinary optical microscope. Single-layer graphene deposited on 300 nm SiO2 appears light purple, and the color turns into darker purple for few-layer graphene samples.
