Real-space detection and manipulation of two-dimensional quantum well states in few-layer MoS2

Quantum confinement has remarkable effects on the band structures and optoelectronic performance of semiconducting materials. The confinement of electronic states developed along van der Waals (vdW) gaps in transition metal dichalcogenides (TMDs) has unique advantages compared with those of artificial quantum wells. Here, we detected the quantized electronic states of few-layered ${\mathrm{MoS}}_{2}$ in real space using scanning tunneling microscope/spectroscopy. Combined with density-functional theory calculations, the quantized states were attributed to quantum-well states (QWSs), and the number of the states was strictly determined by the ${\mathrm{MoS}}_{2}$ layer thickness. We further regulated the QWSs of few-layered ${\mathrm{MoS}}_{2}$ by tuning the strength of interlayer hybridization through directly adjusting the interlayer distance. More importantly, substitutional defects in few-layered ${\mathrm{MoS}}_{2}$ were introduced to control the energy eigenvalues of the QWSs. Our work proves the existence of the interlayer electronic hybridization in conventional weakly coupled vdW interfaces, and provides a way to manipulate the electronic states of few-layered TMD through controlling interlayer hybridization. It also suggests potential applications of quantum-well materials in subband transitions, spin splitting, photoexcitation, and electronic devices.