Dielectric environment as a factor to enhance the production yield of solvent exfoliated graphene

Abstract

High yield production of high quality graphene is essential for its application in electronics, optoelectronics and energy storage devices. Liquid phase exfoliation based methods for obtaining graphene are becoming popular because of their versatility and scalability. These advantages are absent with other growth methods such as mechanical exfoliation using scotch tape and chemical vapor deposition. Here we present a sonication assisted, surfactant free method for liquid phase exfoliation of graphene using solvents with varying dielectric constants. We have shown that the method presented here is capable of producing high yields (1.22 wt%), and exceptionally large sizes (30-50 microns) with a high carrier mobility of 10 000 cm 2 Vs À1 in monolayer graphene. Moreover, it is possible to obtain pristine as well as doped monolayer or bilayer or multilayer graphene with extreme controllability, on any solid substrate. It has been shown that choice of a solvent of a particular dielectric constant and sonication time are key parameters for liquid phase exfoliation. It is further shown that the exfoliation efficiency can be enhanced using solvents with high dielectric constant due to functionalization which has also been supported by density functional theory based electronic structure calculations. We have also tested this fact by using different solvents with similar dielectric constant. This method promises high-end industrial scale synthesis for potential applications in different types of devices, graphene based composites and liquid phase chemistry as well. † Electronic supplementary information (ESI) available: Method to calculate yield of graphene monolayers, associated chart and a brief discussion on electronic structure calculations. See Fig. 4 Atomic force microscopic images of graphene layers obtained by exfoliation of HOPG in (a) toluene and (b) PC. Respective height profiles are also given and indicated by arrows. (c) Histogram showing size distribution of graphene flakes as a function of their respective thickness as observed by AFM. Data corresponds to dispersions sonicated for 12 hours. (d) Size of monolayer graphene as a function of sonication time. It indicates that average size of the graphene flakes varies inversely with the sonication time. Y-axis error bars denote variation in flake sizes over 10-20 flakes. Circles denote the data points and solid line is the linear fit.This journal is

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