**2.3 Exfoliation methods**

Using this knowledge about the cohesive energy, Zhang et al. [17] while working on transport measurements of microscopic graphite devices, fabricated their samples using a micromechanical cleavage process. With a silicon cantilever with a normal force between 10 – 2000nN (**Figure 3a**), they could exfoliate few layers of graphite. These small VDW forces between graphene layers (2 eV/nm2 ) are not easy to achieve for graphene exfoliation but is required. For instance, Hernandez et al. [19] while working on LPE, found that by using a solvent with similar surface tension like graphene, the exfoliation was easier and single layers were obtained.

The requirement of such small forces made researchers to look for more sensible methods. For example, Seunguen Lee and Wei [18] simulate the exfoliation of graphene from HOPG on a SiO2 substrate and called it friction-induced exfoliation (**Figure 3b**). In that process, they used the lubrication properties of HOPG, the corrugation of HOPG combined with the roughness of the substrate. Another similar article is the exfoliation of graphene using the adhesive energy of few layers of graphene on a silicon substrate, while applying an upper velocity force on top of graphite to exfoliate the top layer (**Figure 3c**) [20]. In that study, based on the number of layer and the velocity, they could exfoliate the top layer.

In this paper, we present a new way of graphene exfoliation based on binding and interaction energy between graphene, graphite and a substrate.

*Graphene Exfoliation from HOPG Using the Difference in Binding Energy between Graphite… DOI: http://dx.doi.org/10.5772/intechopen.107142*

**Figure 3.**

*a. Cleavage process using the adhesion energy between graphite and substrate (reprinted from [17] with permission of AIP publishing) b. Friction induced exfoliation (reprinted from [18] with permission of AIP publishing) c. Top layer exfoliation based on velocity and adhesion.*
