Defect free monolayer and bilayer graphene exfoliated by solvent with low dielectric constant.

Defect free mono- and bilayer graphene sheets have been synthesised in low dielectric (k∼5.4) organic solvent i.e. chlorobenzene by liquid phase exfoliation (LPE). Solution containing graphene flakes was transferred on solid substrate and subsequently, dried up to make mono- and bilayer graphene. Characterizations of as synthesized graphene flakes have been carried out by transmission electron microscope, scanning electron microscope and Raman spectroscopy. Graphene exfoliated in chlorobenzene(g-chlorobenzene) does not show D band in Raman spectra, however, a prominent D band is observed for graphene exfoliated in propylene carbonate (g-PC) which has much higher dielectric constant (k∼64). Because of low dielectric constant, chlorobenzene molecules don't interact with graphene while, Propylene Carbonate molecules makea supramolecular bond with graphene due to its (PC) high dielectric constant. This molecular interaction, which has been corroborated by first principle density function calculation, is the origin of Raman D band for g-PC. The distances between solvent molecules and graphene surface are found to be ∼4.34 A° and ∼3.32 A° for g-chlorobenzene and g-PC, respectively by density function theory. [ABSTRACT FROM AUTHOR]