Defect Heterogeneity in Monolayer WS2 Unveiled by Work Function Variance (original) (raw)

Investigation of spatially localized defects in synthetic WS2 monolayers

Physical Review B

While the spatially nonhomogeneous light emission from synthetic WS 2 monolayers is frequently reported in the literature, the nature of this phenomenon still requires thoughtful investigation. Here, we combine several characterization techniques (optical imaging, scanning probe and electron microscopy) along with density functional theory to investigate the presence of substitutional doping localized at narrow regions along the S zigzag edge of WS 2 monolayers. We verified that photoluminescence quenching along narrow regions is not related to grain boundaries but to substitutional impurities of lighter metals at the W sites, which modify the radiative and nonradiative decay channels. We also found potential candidates for occupying the W site through ADF-STEM analysis and discussed their impact on photoluminescence quenching by performing density functional theory calculations. Our findings shed light on how atomic defects introduced during WS 2 monolayer's synthesis impact the crystalline quality and, therefore, the development of high-performance optoelectronic devices based on semiconducting 2D materials.

Disentangling the effects of doping, strain and defects in monolayer WS2 by optical spectroscopy

2019

Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, and water intercalation. Identifying which perturbations are present is usually not straightforward and requires multiple measurements using multiple experimental modalities, which presents barriers when attempting to optimise preparation of these materials. Here, we apply highresolution photoluminescence and differential reflectance hyperspectral imaging in situ to CVD-grown WS2 monolayers. By combining these two optical measurements and using a statistical correlation analysis we are able to di...

Disentangling the effects of doping, strain and disorder in monolayer WS2 by optical spectroscopy

2D Materials, 2019

Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, and water intercalation.

2 4 M ay 2 01 8 Optoelectronic properties of defective MoS 2 and WS 2 monolayers

2018

We theoretically explore the effect of metal and disulphur vacancies on electronic and optical properties of MoS2 and WS2 monolayers based on a Slater-Koster tight-binding model and including the spin-orbit coupling. We show that the vacancy defects create electronic flat bands by shifting the Fermi level towards the valence band, indicating that both types of vacancies may act as acceptor sites. The optical spectra of the pristine monolayers show step-like features corresponding to the transition from spin split valence band to the conduction band minimum, whereas the defective monolayers exhibit additional peaks in their spectra arising from induced midgap states in their band structures. We find that Mo and W vacancies contribute mostly in the low-energy optical spectrum, while the S2 vacancies enhance the optical conductivity mainly in the visible range of the spectrum. This suggests that depending on the type of vacancy, the atomic defects in MoS2 and WS2 monolayers may increas...

Heterogeneous Defect Domains in Single-Crystalline Hexagonal WS2

Advanced materials (Deerfield Beach, Fla.), 2017

Single-crystalline monolayer hexagonal WS2 is segmented into alternating triangular domains: sulfur-vacancy (SV)-rich and tungsten-vacancy (WV)-rich domains. The WV-rich domain with deep-trap states reveals an electron-dedoping effect, and the electron mobility and photoluminescence are lower by one order of magnitude than those of the SV-rich domain with shallow-donor states. The vacancy-induced strain and doping effects are investigated via Raman and scanning photoelectron microscopy.

Studies on chemical charge doping related optical properties in monolayer WS2

Journal of Applied Physics, 2016

Thermal stability of quasi particles, i.e., exciton and trion, and a strong particle-particle interaction significantly tune the optical properties of atomically thin two dimensional (2D) metal dichalcogenides. The present work addresses the effect of inherent defects upon optical properties of chemical vapor deposition grown 1 L-WS 2 and proposes the use of chemical transfer doping as a reversible and simple method for identification of the type of excess charge in the system. Photoluminescence (PL) studies in pristine 1 L-WS 2 show that an additional band at $0.06 eV below trion (X 6) PL band was evolved (at low temperature) which was associated to the bound exciton with charged/ neutral defect. Using 7,7,8,8-Tetracyanoquinodimethane and 2,2-bis1,3-dithiolylidene as p and n-type dopants, respectively, we determined that the inherent defects/metal vacancies, which could be due to the presence of Tungsten metal deficiency, contributed in p-type nature of the pristine 1 L-WS 2. Doping of 2D transition metal dichalcogenides materials with organic molecule via the surface charge transfer method is not only a way to provide a handy way to tailor the electronic and optical properties but also can be used as a tool to determine the nature of defects in the material.