Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films

Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm² Ti₃C₂ films by selective etching of Al, from sputter-deposited epitaxial Ti₃AlC₂ films, in aqueous HF or NH₄HF₂. Films that were about 19 nm thick, etched with NH₄HF₂, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films' resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.