Environmentally stable nanoscale superlubricity of multi-layered Ti3C2Tx MXene

Abstract

With their two-dimensional layered structure, excellent mechanical behavior, and reduced interlayer sliding resistance, early transition metal carbides and nitrides (MXenes) have demonstrated promising solid lubrication properties at the macro- and nanoscale. Although MXenes can exist in several morphologies (multi-layer particles, clay, or single-to-few layer flake dispersions), the dependence of friction on the number of MXene layers is still yet to be fully understood. Here, we present number-of-layer-dependent friction property of single-to-four layer flakes of Ti3C2Tx MXene, produced using a modified MAX synthesis method, via atomic force microscopy with diamond-like-carbon and silicon probes at the nanoscale on silicon substrates. We demonstrate the superlubricity of single-layer Ti3C2Tx MXene as well as the effect of layers of Ti3C2Tx in an inert nitrogen atmosphere (coefficient of friction as low as 0.0039 ± 0.0006 for a bi-layer). Furthermore, we present the long-term stability of Ti3C2Tx's superlubricity up to a month in ambient conditions and up to three months in a vacuum environment. We believe that this investigation of layer-dependent and long-lasting MXene superlubricity at the nanoscale illustrates the potential of implementation of MXene into both space and industrial applications.