Atomic Properties of Monoclinic AgSe Thin Film Grown on SrTiO 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 AgSe thin film, similar to β-AgTe, grown on a SrTiO (STO)(001) substrate by molecular beam epitaxy (MBE). Three different types of AgSe 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 AgSe 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 AgSe and provides insight into its physical properties.