Atomic Properties of Monoclinic Ag₂Se Thin Film Grown on SrTiO₃ Substrate by Molecular Beam Epitaxy

Silver chalcogenides have attracted a great deal of interest due to their promise for exhibiting novel topological properties. Using scanning tunneling microscopy/spectroscopy (STM/S), we have characterized the atomic structure and electronic properties of a monoclinic Ag₂Se thin film, similar to β-Ag₂Te, grown on a SrTiO₃ (STO)(001) substrate by molecular beam epitaxy (MBE). Three different types of Ag₂Se atomic terminations are observed on the surface: (i) homogeneous hexagonal-like, (ii) rough mixed, and (iii) flat zigzag-striped structures. Structural analysis indicates that the different atomic terminations stem from different growth directions, which can be attributed to the lattice mismatch between the substrate and the Ag₂Se film. STS analysis of these atomic terminations uncovers different features near the Fermi level, indicating constituent- and direction-dependent electronic properties. This Letter presents a practical method to grow monoclinic thin film Ag₂Se and provides insight into its physical properties.