Changes of phonon modes and electron transfer induced by interface interactions of Pd/MoS ₂ heterostructures

As functional materials and nano-catalysts, Pd nanoparticles (NPs) are often used to modify two-dimensional (2D) materials. In the heterostructures of metal NPs and 2D transition metal dichalcogenides, the interface atomic configuration and interface effect greatly affect material properties and stability. Therefore, the rational design of interface structures and in-depth analysis of interface interactions are of vital importance for the preparation of specific functional devices. In this work, Pd NPs were deposited on mechanically exfoliated MoS₂ flakes and the epitaxial relationship between Pd and MoS₂ was observed, accompanied by distinct moiré patterns. Raman spectra of the Pd NPs/MoS₂ heterostructure showed an E12g' vibration mode indicative of the local strain in MoS₂. A new vibration mode A'_1g appeared in the higher-frequency direction compared with the pristine A_1g peak. Combined with X-ray photoelectron spectra and density functional theory calculations, the new vibration mode can be attributed to the bonding between Pd and MoS₂. Besides, graphene was inserted between Pd NPs and MoS₂, and the decoupling of the interfacial effect by graphene was investigated. This study will help deepen our understanding on the interaction mechanism between metals and MoS₂, thereby enabling the modulation of optoelectronic properties and the performance of these hybrid materials.