Revealing the Intrinsic Electronic Structure of 2D MoS ₂ Buried Beneath Thick Dielectric Overlayer via Hard X‐ray Photoelectron Spectroscopy

The properties of 2D molybdenum disulfide (MoS₂) strongly depend on its interactions with surrounding materials, making characterization in device-like configurations essential. In this study, a MoS₂ sample with a 20-nm-thick top AlOx layer (embedded MoS₂) was used as the dielectric-semiconductor heterostructure in real devices. Hard X-ray photoelectron spectroscopy (HAXPES) is the primary analytical technique employed for analyzing the embedded MoS₂ samples. Compared to conventional X-ray photoelectron spectroscopy (XPS) using an Al-Kα source, HAXPES with a Cr-Kα source offers greater information depth (ID) and broader access to electronic structures. This enables probing of the S KLL, Mo 2p3, and S 1s regions, in addition to the Mo 3d and S 2p regions, at an ID more than twice that of conventional XPS. A combination of Raman spectroscopy, transmission electron microscopy, X-ray diffraction analysis, and synchrotron-based HAXPES is used to optimize the monoatomic Ar ion beam sputtering conditions for electronic structure analysis of MoS₂, with the validation of the results. Consequently, the optimized HAXPES analysis enables the provision of the intrinsic electronic structure of MoS₂ free from sputtering damage. It has been demonstrated that the inherent chemical bonding state of MoS₂ prior to AlOx deposition is fully preserved even in the embedded MoS₂ sample.