Probing Interfacial Surface State Excitons in Nanoscale Synthesized Cu _x S/MoS ₂ Heterostructure

Two dimensional (2D) layer integration of different materials facilitates new functionalities in material engineering to produce novel structures with specialized properties. Fabrication of large-scale 2D heterostructure with atomically clean interface, and unveiling the distinct interlayer transition, is a challenging process. In this paper, the vertical heterostructure of copper sulfide (Cu _x S) and molybdenum disulfide (MoS ₂ ) nanosheets is synthesized by sulfurization of pre-deposited metal films. Optical bandgap transition and phonon vibration frequency are observed in the heterojunction area with respect to individual nanosheets. Raman shift in phonon vibration modes of MoS ₂ shows the interlayer coupling effect. Photoluminescence (PL) intensity of monolayer MoS ₂ is quenched due to bandgap offset interlayer transition. Bandgap alignment of Cu _x S (1 < x < 2) with MoS ₂ is a tunable staggered symmetry that yields charge transfer at the heterostructure interface. Photoexcited electron–hole pairs are moving across the interface much faster than recombining into the intralayer excitons. The synthesized Cu _x S/MoS ₂ heterostructure is well defined over a large area, with controllable thickness and a scalable position. Heterostructure has great potential for future device applications in optoelectronics based on optical excitonic response and charge carrier dynamics.