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Two-dimensional (2D) materials received large amount of studies because of the enormous potential in basic science and industrial applications. Monolayer Pd2Se3 is a fascinating 2D material that was predicted to possess excellent thermoelectric, electronic, transport, and optical properties. However, the fabrication of large-scale and high-quality monolayer Pd2Se3 is still challenging. Here, we report the synthesis of large-scale and high-quality monolayer Pd2Se3 on graphene-SiC (0001) by a two-step epitaxial growth. The atomic structure of Pd2Se3 was investigated by scanning tunneling microscope (STM) and confirmed by non-contact atomic force microscope (nc-AFM). Two subgroups of Se atoms have been identified by nc-AFM image in agreement with the theoretically predicted atomic structure. Scanning tunneling spectroscopy (STS) reveals a bandgap of 1.2 eV, suggesting that monolayer Pd2Se3 can be a candidate for photoelectronic applications. The atomic structure and defect levels of a single Se vacancy were also investigated. The spatial distribution of STS near the Se vacancy reveals a highly anisotropic electronic behavior. The two-step epitaxial synthesis and characterization of Pd2Se3 provide a promising platform for future investigations and applications. [ABSTRACT FROM AUTHOR]

Using the first principle method, we investigate the influence of Sr/Ti ratio on the atomic structure and dislocation behavior of Srn+1TiO3n+1 (Ruddlesden-Popper phase) and SrnTin+1O3n+2 (Magnéli phase). A linear lattice expansion versus the Sr/Ti ratio exhibits in the Ruddlesden-Popper and Magnéli phases. The Ruddlesden-Popper phase has lower formation energy and superior structural stability than the Magnéli phase. The two phases show different dislocation behaviors and it is found that a possibly preferred slip system (110) {110} emerges in the two phases, and the dislocations are more likely to dissociate into partial dislocations in Magnéli phases. [ABSTRACT FROM AUTHOR]