Flux-grown large Ti3AlC2 single crystals with well-defined structural and electronic properties toward millimetre-scale MXenes

Abstract Ti₃AlC₂, a typical MAX phase compound, serves as the parent structure of Ti₃C₂Tₓ MXenes, the most extensively studied members of the MXene family for diverse applications. Despite increasing interest, most studies of Ti₃AlC₂ rely on polycrystalline samples, limiting accurate determination of its intrinsic physical properties. The synthesis of large, high-quality single crystals therefore remains essential for probing fundamental electronic, optical, and transport behaviour. Here, we report the growth of large Ti₃AlC₂ single crystals using a TiAl₃ flux-assisted method. The crystals exhibit excellent structural quality, with individual flakes exceeding 1 cm in length and basal-plane areas up to ~36 mm². Hall measurements on individual flakes reveal a high carrier density of ~10²¹ cm⁻³, while polarisation-resolved Raman spectra show a nearly circular intensity pattern, indicating optical isotropy within the basal plane. Scanning tunnelling microscopy on freshly cleaved crystals reveals non-flat surface topography related to cleavage termination. First-principles calculations indicate that cleavage predominantly occurs between Ti–Al layers and predict distinct surface-dependent band structures and Fermi surfaces associated with Al- and Ti-terminated surfaces. Chemical etching of the MAX phase yields millimetre-scale Ti₃C₂Tₓ flakes that can be mechanically exfoliated onto chips. Raman spectra show a strong G band at ~1550 cm⁻¹ without a discernible D band, indicating ultralow-defect sp²-like carbon structures. Devices fabricated from these flakes exhibit symmetric I–V characteristics and negligible gate modulation, confirming metallic behaviour and good electrical contact. This work establishes a scalable route to large Ti₃AlC₂ single crystals and provides insight into their intrinsic properties, supporting future MXene-based device technologies.