Atomic-Scale Defect Engineering in Two-Dimensional Transition Metal Dichalcogenides (TMDCs)

Controlled introduction of sulfur vacancies in MoS2 monolayers has been shown to enhance catalytic activity for hydrogen evolution reactions (HER) by a factor of 10^3 compared to pristine samples. Density functional theory (DFT) calculations reveal that these vacancies lower the Gibbs free energy barrier to ~0.08 eV, approaching the theoretical limit for HER efficiency. This defect engineering approach opens new avenues for sustainable energy technologies.

The impact of defects on electronic transport in TMDCs has been quantified using scanning tunneling microscopy (STM) and Kelvin probe force microscopy (KPFM). Single-atom vacancies induce localized states within the bandgap (~1 eV), leading to carrier trapping and reduced mobility (<10 cm^2/Vs). However, passivation with atomic hydrogen restores mobility values above 100 cm^2/Vs while preserving defect-induced functionalities like enhanced photoresponsivity (~10^4 A/W).

Defect-mediated exciton localization in TMDCs has been studied using cathodoluminescence spectroscopy at cryogenic temperatures (~4 K). Localized excitons exhibit linewidths as narrow as 50 µeV, making them ideal candidates for quantum emitters in integrated photonic circuits. The spatial distribution of these defects can be controlled via focused ion beam patterning with sub-10 nm precision.

Thermal stability of defects in TMDCs under operational conditions has been investigated using in situ transmission electron microscopy (TEM). Sulfur vacancies remain stable up to temperatures of ~500°C but migrate rapidly above this threshold, leading to coalescence into larger voids (~2 nm diameter). Understanding these dynamics is crucial for device reliability under high-power operation.

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