Optical Signatures of Defect Centers in Transition Metal Dichalcogenide Monolayers

Abstract

Even the best quality 2D materials have non‐negligible concentrations of vacancies and impurities. It is critical to understand and quantify how defects change intrinsic properties, and use this knowledge to generate functionality. This challenge can be addressed by employing many‐body perturbation theory to obtain the optical absorption spectra of defected transition metal dichalcogenides. Herein metal vacancies, which are largely unreported, show a larger set of polarized excitons than chalcogenide vacancies, introducing localized excitons in the sub‐optical‐gap region, whose wave functions and spectra make them good candidates as quantum emitters. Despite the strong interaction with substitutional defects, the spin texture and pristine exciton energies are preserved, enabling grafting and patterning in optical detectors, as the full optical‐gap region remains available. A redistribution of excitonic weight between the A and B excitons is visible in both cases and may allow the quantification of the defect concentration. This work establishes excitonic signatures to characterize defects in 2D materials and highlights vacancies as qubit candidates for quantum computing.

Effect of Ar-ion irradiation on electrical transport of WS2 monolayer

“…The exposed sample exhibits shifted the peak position of the PL, which is ∼14.6 meV. The shift in peak position toward the lower energy suggests negatively charged trions forming, which confirms the incorporation of S-vacancies [26,39,40].…”

“…Chalcogen and transition metal vacancies lead to different types of free carriers, contributing to electrical transport [15,16,[25][26][27]. Generally, chalcogen vacancies are intrinsic in 2D-TMDs due to low formation energies, for example, around 2.76 eV for S-vacancy and 10.84 eV for W-vacancy in monolayer WS 2 , based on theoretical investigations by MC de Melo et al [26]. Doping foreign atoms can substantially alter the optical and electrical response and induce new functionalities such as room-temperature ferromagnetism [24,25].…”

“…We can enhance electrical transport by using vacancies; for instance, sulfur vacancies in the WS 2 monolayer increase carrier mobility and reduce threshold voltage [18,19,27] due to increased free carrier density and reduced effective mass. Sulfur vacancies in the WS 2 monolayer make it W-rich, transferring additional levels [23,26] to the conduction band and acting as electron donor sites, inducing n-type characteristics. In contrast, W-vacancies make the material Srich, transferring additional states to the valence band, making it hole-rich and inducing p-type behavior, though they have higher formation energies, as predicted by theoretical and experimental investigations [15,16,26].…”

“…Sulfur vacancies in the WS 2 monolayer make it W-rich, transferring additional levels [23,26] to the conduction band and acting as electron donor sites, inducing n-type characteristics. In contrast, W-vacancies make the material Srich, transferring additional states to the valence band, making it hole-rich and inducing p-type behavior, though they have higher formation energies, as predicted by theoretical and experimental investigations [15,16,26]. Reports present several ways to incorporate defects in 2D-TMDs [15,16,27,29,30] ranging from site-specific to over a large area.…”

Rapid multiplex ultrafast nonlinear microscopy for material characterization

“…We further show via simulations that non-equidistant spacing of the timedomain sampling points allows for the retrieval of a more extensive range of decay times at only a small cost of reduced fit reliability. Given the broad usability of four-wave-mixing-based ultrafast imaging from two-dimensional quantum materials [28] and defects in graphene [45] to distinguishing benign from malignant melanoma [46], these method advancements constitute an important step forward toward material inspection in both research and industrial settings, and potentially life-science and medical imaging.…”