Buffer-Assisted Epitaxy of Large-Area Ultraflat θ-Tellurene with Mirror Symmetry

Tellurene, covalently bonded tellurium (Te) atoms, is one of the most chemically tractable materials in the low-dimensional community. However, the monoelemental nature and structural simplicity limit synthesis-accessible tellurene merely in the β-phase, assembled by helical Te chains with a trigonal lattice. The nonplanar structure confines tellurene at the micrometer scale and poses technological challenges toward van der Waals integrations. Here, we report an ultraflat phase of tellurene, named as θ-tellurene, over the centimeter scale via a buffer-assisted epitaxial method on the Au(100) crystal. Such a tellurene phase possesses well-aligned flat-lying 1D Te chains in monatomic zigzag configuration, as verified by scanning tunneling microscopy, noncontact atomic force microscopy, scanning transmission electron microscopy, and density functional theory calculations. Ultraflat θ-tellurene evolves through extended Ostwald ripening and dissociation-triggered transformation on a Te buffer layer, initiated and controlled by postannealing treatment. θ-Tellurene exhibits an n-type semiconducting behavior with a band gap of ∼1.55 eV and exhibits 2-fold in-plane mirror symmetry.