Boltzmann Sigmoidal Modulation of Vanadium Doping in Monolayer MoS2 by Potassium Iodide.

The atomic thickness of two-dimensional (2D) semiconductors makes conventional postgrowth substitutional doping highly challenging. Instead, such atomic substitution can be more effectively achieved in situ through chemical vapor deposition synthesis. However, the mechanistic details governing this growth process have remained poorly understood. Using V-doped monolayer MoS2 as a model system, this work elucidates its growth mechanism and doping tunability facilitated by a potassium iodide (KI) promoter. A Raman spectroscopic probe, established through correlation with scanning transmission electron microscopy, was developed to quantify the V dopant concentration and distribution uniformity. Systematic growth experiments and detailed characterizations revealed that doping saturation levels were significantly below the precursor feeding ratio. This saturation phenomenon could be modulated by KI dosage following a Boltzmann sigmoid function, indicative of an iodide-activated doping mechanism compatible with the edge passivation substitution (EPS) model. Our findings advance the doping theory in low-dimensional systems and provide essential insights into achieving controlled heteroatom substitution in 2D semiconductors.