## 1 Introduction  
Post-transition metal dichalcogenides (PTMCs), composed of III-VA metal elements (Ga, In, Sn, Bi etc.) and chalcogen elements (S, Se, Te), are a new class of layered two-dimensional (2D) materials that have attracted extensive study recently. In addition to the highly anisotropic lattice structure and unique electronic structures, many outstanding electrochemical, thermoelectric, and optoelectronic properties were observed in PTMCs. Therefore, PTMCs have been applied in many fields like electrochemistry [1, 2], electronics [3, 4], optoelectronics [5, 6] and gas sensing [7]. As a prominent member of PTMCs, SnSe\({}_{2}\) is an intrinsic layered semiconductor, exhibiting considerable bandgap and excellent thermoelectric properties like ultra-low thermal conductivity and high carrier mobility [8, 9].  
Together with a high abundance of Sn, SnSe\({}_{2}\) shows potential applications in optoelectronics [10; 11; 12; 13], thermoelectric devices [14], lithium-ion batteries [15] and phase change memory [16; 17].  
In addition, intriguing physical properties like charge density wave (CDW), superconductivity and interfacial polarons were observed in SnSe\({}_{2}\) from previous works [18; 19; 20]. The interface properties of monolayer (ML) SnSe\({}_{2}\) could be effectively tuned by choosing different substrates. For examples, a recent study showed that ML and bilayer SnSe\({}_{2}\) films grown on Si(111) undergo a commensurate CDW transition at \(T_{\rm C}\sim\)78 K driven by Fermi surface nesting between symmetry inequivalent electron pockets, forming a corresponding (2 \(\times\) 2) superlattice [20]. In addition, the formation of interfacial polarons induced by charge accumulation and electron-phonon coupling between SrTiO\({}_{3}\) and SnSe\({}_{2}\) was evidenced [19]. Furthermore, the superconductivity in SnSe\({}_{2}\), which can be modulated by cation intercalation [21] and dielectric gating techniques [22], was reported to be enhanced in the epitaxial SnSe\({}_{2}\) on graphitized SiC(0001) substrate [18]. However, there are only a few studies on SnSe\({}_{2}\) film grown on Si(111), with the study on direct characterization of band structures still lacking in particular. In this paper, we synthesize SnSe\({}_{2}\) films on Si(111) by molecular beam epitaxy (MBE), and employ in situ reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) to characterize the atomic and electronic structures of them. We found that the SnSe\({}_{2}\) shows layer-by-layer growth mode on \(\sqrt{3}\)-Sn/Si(111) substrate with a high quality of flatness. The interfacial charge transfer effect is observed in the SnSe\({}_{2}\) film grown on \(\sqrt{3}\)-Sn/Si(111) substrate. Moreover, an emerging band above the original valence band of bulk SnSe\({}_{2}\) is found in the SnSe\({}_{2}\) thin film, resulting in the reduction of the indirect band gap. This emerging band is suggested to be induced by the interfacial strain-driven structural phase transition of the grown SnSe\({}_{2}\). Our results provide important information for further applications of SnSe\({}_{2}\) film in 2D electronic devices.