Functionalization of graphene and few-layer graphene films in an hydrofluoric acid aqueous solution

Abstract

The possibility of the controlled modification of the properties of graphene and few-layer graphene significantly extends the scope of their potential applications. Conditions for the chemical modification of graphene and few-layer graphene in an hydrofluoric acid aqueous (HF) solution were revealed in this work. The following changes in the properties of films upon their treatment in an aqueous HF solution were observed: a sharp (by 5–7 orders of magnitude) jump in the resistance of samples, the suppression of characteristic peaks in Raman spectra, the occurrence of peaks from fluorine ions F (687.7 eV) and C-F bonds (288 eV) in X-ray photoelectron spectroscopy (XPS) spectra, and the formation of a nanorelief on the surface. The reaction with HF possesses an activation character (with an energy of 1.4 eV), depending on the temperature; the reaction proceeds in a narrow range of concentrations of HF solution and is reversible. An array of experimental data made it possible to suggest that the functionalization of films was due to fluorination. The recovery of the conductivity of films after the annealing of samples at a temperature of 450°C (the energy of activation of the annealing ∼2 eV) is one of the confirmations of the fluorination process. It was shown that the fluorination reaction in an aqueous HF solution was initiated on the grain boundaries of polycrystalline films of graphene and few-layer graphene. It was found that the interaction of few-layer graphene with HF depended significantly on the thickness of samples and their preliminary treatment. A model for the fluorination of a few-layer film based on the corrugating of layers because of the difference in the lattice constants of graphene and fluorographene was suggested.