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

ABSTRACT The properties of 2D molybdenum disulfide (MoS ₂ ) strongly depend on its interactions with surrounding materials, making characterization in device‐like configurations essential. In this study, a MoS ₂ sample with a 20‐nm‐thick top AlO _x layer (embedded MoS ₂ ) 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 MoS ₂ 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 MoS ₂ , with the validation of the results. Consequently, the optimized HAXPES analysis enables the provision of the intrinsic electronic structure of MoS ₂ free from sputtering damage. It has been demonstrated that the inherent chemical bonding state of MoS ₂ prior to AlO _x deposition is fully preserved even in the embedded MoS ₂ sample.