Defect Heterogeneity in Monolayer WS₂ Unveiled by Work Function Variance

Abstract

Defects are commonly found in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials. Such defects usually dictate the optical and electrical properties of TMDs. It is thus important to develop techniques to characterize the defects directly with good spatial resolution, specificity, and throughput. Herein, we demonstrate that Kelvin probe force microscopy (KPFM) is a versatile technique for this task. It is able to unveil defect heterogeneity of 2D materials with a spatial resolution of 10 nm and energy sensitivity better than 10 meV. KPFM mappings of monolayer WS2 exhibit interesting work function variances that are associated with defects distribution. This finding is verified by aberration-corrected scanning transmission electron microscopy and density functional theory calculations. In particular, a strong correlation among the work function, electrical and optical responses to the defects is revealed. Our findings demonstrate the potential of KPFM as an effective tool for exploring the intrinsic defects in TMDs.

Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

“…Additionally, it was clear that the oxidation influenced the bilayer region differently than the monolayer regions. Interestingly, bilayers atop the oxidized region showed a potential higher even than the basal plane, whereas bilayers on the basal plane showed a much lower potential consistent with literature values in pristine TMD flakes 23,61,62 . This is hypothesized to be due to potentially different oxidative states within the material such as chemisorption of oxygen to the bilayer rather than physisorption.…”

Charge Transfer Properties of Heterostructures Formed by Bi2O2Se and Transition Metal Dichalcogenide Monolayers

“…Since larger surface potential corresponds to lower work function and thus higher Fermi energy, the Fermi level of Bi 2 O 2 Se is higher than that of WS 2 by that amount. By using the previously reported Fermi level of −4.81 eV for monolayer WS 2 , [ 30 ] we find a Fermi level of −4.45 eV for Bi 2 O 2 Se monolayer, as indicated in Figure 2c. This result is consistent with previous works on Bi 2 O 2 Se nanoplates.…”

Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W‐Au Alloy Substrates

“…This applies to most TMD MLs, in which the single chalcogen vacancy prevails as an intrinsic defect. [24] Removal of an additional sulfur atom at the bottom layer creates V S2 , which requires nearly twice the formation energy of V S . Note, the formation energy of V S2 continues to increase with sulfur chemical potential increasing and sulfur divacancy becomes the most unfavorable defect in the sulfur-rich condition.…”

“…Currently, antisite defects have only randomly appeared in 2D TMDs grown by chemical vapor deposition, molecular beam epitaxy, and physical vapor deposition methods. [18,19,24] Antisite defects do not appear as frequently as other point defects during the growth since they tend to have much higher formation energies, and are thus thermodynamically unfavorable. Therefore, reducing their formation energy during growth is required to form antisite defects in 2D materials.…”