Interfacial properties of 2D WS2 on SiO2 substrate from X-ray photoelectron spectroscopy and first-principles calculations

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Two-dimensional (2D) WS 2 films were deposited on SiO 2 wafers, and the related interfacial properties were investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Using the direct (indirect) method, the valence band offset (VBO) at monolayer WS 2 /SiO 2 interface was found to be 3.97 eV (3.86 eV), and the conduction band offset (CBO) was 2.70 eV (2.81 eV). Furthermore, the VBO (CBO) at bulk WS 2 /SiO 2 interface is found to be about 0.48 eV (0.33 eV) larger due to the inter-layer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS 2 /SiO 2 heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO 2 . The theoretical calculations further reveal a binding energy of 75 meV per S atom and the totally separated partial density of states, indicating a weak interaction and negligible Fermi level pinning effect between WS 2 monolayer and SiO 2 surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS 2 /SiO 2 heterostructures.