New graphene derivative with N-methylpyrrolidone: suspension, structural, optical and electrical properties

In the present study, a new graphene derivative created by the interaction of 2-5 nm thick multi-graphene suspension flakes with N-methylpyrrolidone (NMP) was examined. It was found that the conductivity of the films prepared from the suspensions obtained using the treatment of initial graphene suspensions in NMP decreased after additional annealing in the temperature range from 60 to 200 °C by six to seven orders of magnitude. The annealing temperature required for this decrease of conductivity shows a decrease with diminishing suspension flake sizes. The obtained high-resistivity films demonstrate low leakage currents (10^-7-10^-8 A cm^-2), an ultra-low charge in the functionalized films (-(1-4) × 10¹⁰ cm^-2), a relatively high dielectric constant of 7.0-9.0, and a breakdown electric-field strength of (2-3) × 10⁵ V cm^-1. The possibility to restore the conductivity to a resistance value of 43 kΩ sq^-1 in the upper layer of the films prepared from the functionalized suspension and the possibility to obtain an unexpectedly high value of electron mobility μ≈ 55-65 cm² V^-1 s^-1 in the recovered few top layers (in comparison with the electron mobility of 0.1-1 cm² V^-1 s^-1 in the films prepared from the initial suspension) was shown. The combination of the useful properties of the films prepared from the functionalized graphene suspension together with the possibility to form heterostructures using the simple chemical recovery of the top layer and the expected flexibility of such heterostructures, makes these films promising for a wide range of applications, including the fabrication of dielectric films for van der Waals heterostructures and structures intended for flexible and printed electronics.