  Two-dimensional (2D) transition metal dichalcogenides (TMDs) are prospective
materials for quantum devices owing to their inherent 2D confinements. They
also provide a platform to realize even lower-dimensional in-plane electron
confinement, e.g., 0D quantum dots, for exotic physical properties. However,
fabrication of such laterally confined monolayer (1L) nanostructure in 1L
crystals remains challenging. Here we report the realization of 1L ReS2 quantum
dots epitaxially inlaid in 1L MoS2 by a two-step chemical vapor deposition
method combining with plasma treatment. The lateral lattice mismatch between
ReS2 and MoS2 leads to size-dependent crystal structure evolution and in-plane
straining of the 1L ReS2 nanodots. Optical spectroscopies reveal the abnormal
charge transfer between the 1L ReS2 quantum dots and the MoS2 matrix, resulting
from electron trapping in the 1L ReS2 quantum dots. This study may pave the way
for realizing in-plane quantum-confined devices in 2D materials for potential
applications in quantum information.
