  The reliable production of two-dimensional crystals is essential for the
development of new technologies based on 2D materials. However, current
synthesis methods suffer from a variety of drawbacks, including limitations in
crystal size and stability. Here, we report the fabrication of large-area,
high-quality 2D tellurium (tellurene) using a substrate-free solution process.
Our approach can create crystals with a process-tunable thickness, from
monolayer to tens of nanometres, and with lateral sizes of up to 100 um. The
chiral-chain van der Waals structure of tellurene gives rise to strong in-plane
anisotropic properties and large thickness dependent shifts in Raman
vibrational modes, which is not observed in other 2D layered materials. We also
fabricate tellurene field-effect transistors, which exhibit air-stable
performance at room temperature for over two months, on off ratios on the order
of 106 and field-effect mobilities of around 700 cm2 per Vs. Furthermore, by
scaling down the channel length and integrating with high-k dielectrics,
transistors with a significant on-state current density of 1 A mm-1 are
demonstrated.
