Vanadium-vacancy defect complexes in monolayer tungsten diselenide

We present a comprehensive study of the formation of defect complexes of vanadium substitutional dopants and selenium vacancies in monolayer tungsten diselenide. Different defect complexes were identified and analyzed by the statistical treatment of scanning transmission electron microscope (STEM) datasets. Using density functional theory (DFT) calculations, we studied the thermodynamic stability of these defect complexes under experimental growth conditions. Both theory and experiment reveal that vanadium substitutional defects lower the formation energy of surrounding selenium vacancies. Increasing the vanadium concentration results in a larger density and average size of the vanadium-vacancy complexes. Nevertheless, the formation of larger complexes requires higher energy costs, and the most commonly observed defect complex configuration consists of a single vacancy adjacent to a vanadium defect. Our results pave the way for exploration of engineering impurity-vacancy complexes by substitutional doping in 2D TMDs.