Exfoliation of Non-Oxidized Graphene Flakes for Scalable Conductive Film

Abstract

The increasing demand for graphene has required a new route for its mass production without causing extreme damages. Here we demonstrate a simple and cost-effective intercalation based exfoliation method for preparing high quality graphene flakes, which form a stable dispersion in organic solvents without any functionalization and surfactant. Successful intercalation of alkali metal between graphite interlayers through liquid-state diffusion from ternary KCl-NaCl-ZnCl(2) eutectic system is confirmed by X-ray diffraction and X-ray photoelectric spectroscopy. Chemical composition and morphology analyses prove that the graphene flakes preserve their intrinsic properties without any degradation. The graphene flakes remain dispersed in a mixture of pyridine and salts for more than 6 months. We apply these results to produce transparent conducting (∼930 Ω/□ at ∼75% transmission) graphene films using the modified Langmuir-Blodgett method. The overall results suggest that our method can be a scalable (>1 g/batch) and economical route for the synthesis of nonoxidized graphene flakes.

A simple and flexible route to large-area conductive transparent graphene thin-films

“…4a and b). These results indicate that the properties of our pristine films are comparable to the best results reported for films obtained by LB film deposition [5,47] (Fig. S8 for the wavelength dependence of transmittance).…”

“…According to our observations, thin films are composed of overlapping graphene sheets with a small number of edges protruding out of the plane of films as shown in Fig. S2c and Sd, which is considered as a major contribution to the overall roughness [4,5,47]. Furthermore, Raman spectra (excitation wavelength 633 nm, Fig.…”

“…This is a clear illustration that the presented route, even in the case of acceptortype GIC, which some may consider to be resembling Hummers method, actually avoids irreversible graphite/graphene oxidation, i.e., it creates an intercalation compound instead of graphene oxide [28]. It was observed that after drying, as-prepared films have large variations in sheet resistance between experiments but these variations in sheet resistance are eliminated by thermal annealing [47] at 400 C in a flow of dry nitrogen. Thermal annealing is accompanied by an approximately 60 fold increase in conductivity for both acceptor and donor-type derived films.…”

Multilayer Graphene Films Obtained by Dip Coating Technique

“…Our results indicate a lower light transmitted reaching 10 and 20% compared with those related to depositions of non-oxidized graphene flakes, 30 graphene oxide and graphene oxide with nanowires and nanofibers 12,13,29 to which transmittances in the range 55-75% were reported.…”

“…Nevertheless Yun et al 13 obtained this resistance at around 86% of light transmitted, while our results are around 10%. Park et al 30 deposited graphene films chemically exfoliated and using Langmuir-Blodgett method with 930Ω/square at 75% of transmittance. Despite the presence of more MLG flakes in the surface confirmed by optical images (Figure 3) and low light transmitted (Figure 2), the sample obtained with dispersion C with 35 immersions probably reached a limit value for the electric resistance and any excess of MLG flakes does not act in the decrease of this electric resistance value.…”