Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films

TLDR

Since graphene’s discovery, the search for two‑dimensional materials has accelerated, leading to the recent discovery of MXenes—conductive, hydrophilic transition‑metal carbides and carbonitrides that have so far been produced only as powders, flakes, or colloidal solutions. The authors fabricated ~1 × 1 cm² Ti₃C₂ films by selectively etching Al from sputter‑deposited epitaxial Ti₃AlC₂ layers using aqueous HF or NH₄HF₂. The ~19‑nm Ti₃C₂ films etched with NH₄HF₂ exhibit ~90 % visible‑to‑IR transmittance, metallic conductivity down to ~100 K, and below that temperature a resistivity rise with negative magnetoresistance indicative of weak localization, demonstrating their potential for electronic, photonic, and sensing applications.

Abstract

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.