Molecular Beam Epitaxy and Electronic Structure of Atomically Thin Oxyselenide Films.

Atomically thin oxychalcogenides have been attracting intensive attention for their fascinating fundamental properties and application prospects. Bi O Se, a representative of layered oxychalcogenides, has emerged as an air-stable high-mobility 2D semiconductor that holds great promise for next-generation electronics. The preparation and device fabrication of high-quality Bi O Se crystals down to a few atomic layers remains a great challenge at present. Here, molecular beam epitaxy (MBE) of atomically thin Bi O Se films down to monolayer on SrTiO (001) substrate is achieved by co-evaporating Bi and Se precursors in oxygen atmosphere. The interfacial atomic arrangements of MBE-grown Bi O Se/SrTiO are unambiguously revealed, showing an atomically sharp interface and atom-to-atom alignment. Importantly, the electronic band structures of one-unit-cell (1-UC) thick Bi O Se films are observed by angle-resolved photoemission spectroscopy (ARPES), showing low effective mass of ≈0.15 m and bandgap of ≈0.8 eV. These results may be constructive to the synthesis of other 2D oxychalcogenides and investigation of novel physical properties.