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

TL;DR

This study combines experimental XPS and first-principles calculations to analyze the interfacial electronic properties of 2D WS2 on SiO2, revealing band offsets, weak interaction, and Type I energy-band alignment.

Contribution

It provides a comprehensive analysis of the interfacial electronic structure of 2D WS2 on SiO2 using combined experimental and theoretical methods, which was not previously detailed.

Findings

Valence band offset (VBO) ~3.97 eV (monolayer)

Conduction band offset (CBO) ~2.70 eV (monolayer)

Weak interaction and negligible Fermi level pinning

Abstract

Two-dimensional (2D) WS2 films were deposited on SiO2 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 WS2/SiO2 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 WS2/SiO2 interface is found to be about 0.48 eV (0.33 eV) larger due to the interlayer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS2/SiO2 heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO2. 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 WS2 monolayer and SiO2 surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS2/SiO2 heterostructures.