Elastic properties of 2D Ti ₃ C ₂ T _<i>x</i> MXene monolayers and bilayers

Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a large class of materials that are finding numerous applications ranging from energy storage and electromagnetic interference shielding to water purification and antibacterial coatings. Yet, despite the fact that more than 20 different MXenes have been synthesized, the mechanical properties of a MXene monolayer have not been experimentally studied. We measured the elastic properties of monolayers and bilayers of the most important MXene material to date, Ti₃C₂T _<i>x</i> (T _<i>x</i> stands for surface termination). We developed a method for preparing well-strained membranes of Ti₃C₂T _<i>x</i> monolayers and bilayers, and performed their nanoindentation with the tip of an atomic force microscope to record the force-displacement curves. The effective Young's modulus of a single layer of Ti₃C₂T _<i>x</i> was found to be 0.33 ± 0.03 TPa, which is the highest among the mean values reported in nanoindentation experiments for other solution-processed 2D materials, including graphene oxide. This work opens a pathway for investigating the mechanical properties of monolayers and bilayers of other MXenes and extends the already broad range of MXenes' applications to structural composites, protective coatings, nanoresonators, and membranes that require materials with exceptional mechanical properties.