Visualization and quantification of transition metal atomic mixing in Mo1−xWxS2 single layers

Abstract

The alloying behaviour of materials is a well-known problem in all kinds of compounds. Revealing the heteroatomic distributions in two-dimensional crystals is particularly critical for their practical use as nano-devices. Here we obtain statistics of the homo- and heteroatomic coordinates in single-layered Mo1−xWxS2 from the atomically resolved scanning transmission electron microscope images and successfully quantify the degree of alloying for the transition metal elements (Mo or W). The results reveal the random alloying of this mixed dichalcogenide system throughout the chemical compositions (x=0 to 1). Such a direct route to gain an insight into the alloying degree on individual atom basis will find broad applications in characterizing low-dimensional heterocompounds and become an important complement to the existing theoretical methods.

Growth and optical properties of Nb-doped WS2 monolayers

“…However, the details of such defect sites are still unclear, and PL can generally be observed only at low temperature. These issues may be resolved by the controlled fabrication of defect states, which is an important challenge in understanding and using TMDC atomic layers as quantum light sources.In general, defect states in low-dimensional materials are created through several mechanisms, including atomic vacancy formation, 12) impurity doping, [13][14][15][16] and chemical functionalization. 17) In this study, we have investigated impuritydoped WS 2 monolayers as a model system.…”

“…These results are similar WS 2 growth by halide-assisted CVD reported previously. 21) For structural characterization, we conducted annular dark field (ADF)-STEM observations of a monolayer sample 13,14,23) It should be noted that the STEM images of the doped samples are different from those of pure WS 2 monolayers as observed previously. 14) Through a statistical analysis of the ADF-STEM images obtained at six different positions of the same grain, the ratio of dark spots is estimated to be 0.55 ± 0.03%.…”

“…21) For structural characterization, we conducted annular dark field (ADF)-STEM observations of a monolayer sample 13,14,23) It should be noted that the STEM images of the doped samples are different from those of pure WS 2 monolayers as observed previously. 14) Through a statistical analysis of the ADF-STEM images obtained at six different positions of the same grain, the ratio of dark spots is estimated to be 0.55 ± 0.03%. It should be noted that it is quite difficult to conduct an elemental analysis on the present samples by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDX) because of the very weak signals from the Nb atoms.…”

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2

“…[52][53][54][55] Figure 2 (inset) shows the eight chalcogen sites that substitutional sulfur may occupy in the ReSe 2 unit cell. The number of arrangements of r sulfur atoms on the n chalcogen sites of the primitive unit cell (considered as non-equivalent) is given by n C r with n = 8.…”

DFT study of structural and electronic properties of MoS2(1−x)Se2x alloy (x = 0.25)

“…Photoluminescence (PL) characterization of the Mo (1-x) W x S 2 monolayer alloys has shown the continuously tuned emission from 1.82 eV (reached at x ¼ 0.20) to 1.99 eV (reached at x ¼ 1). 8,9 Moreover, centimeter-scale and highquality Mo 0.5 W 0.5 Se 2 alloy films were obtained on both a rigid SiO 2 /Si substrate and a flexible polyimide (PI) substrate. 10 For the second type of alloy, two different chalcogen atoms present in the alloy [MoS 2(1-x) Se 2x (Refs.…”