Bandgap modulation in the two-dimensional core-shell-structured monolayers of WS2

Abstract

Tungsten disulfide (WS 2 ) has tunable bandgaps, which are required for diverse optoelectronic device applications. Here, we report the bandgap modulation in WS 2 monolayers with two-dimensional core-shell structures formed by unique growth mode in chemical vapor deposition (CVD). The core-shell structures in our CVD-grown WS 2 monolayers exhibit contrasts in optical images, Raman, and photoluminescence spectroscopy. The strain and doping effects in the WS 2 , introduced by two different growth processes, generate PL peaks at 1.83 eV (at the core domain) and 1.98 eV (at the shell domain), which is distinct from conventional WS 2 with a primary PL peak at 2.02 eV. Our density functional theory (DFT) calculations explain the modulation of the optical bandgap in our coreshell-structured WS 2 monolayers by the strain, accompanying a direct-to-indirect bandgap transition. Thus, the core-shell-structured WS 2 monolayers provide a practical method to fabricate lateral heterostructures with different optical bandgaps, which are required for optoelectronic applications.

The Hidden Flower in WS2 Flakes: A Combined Nanomechanical and Tip-Enhanced Raman Exploration

“…The growth mechanism changes to a more sulfur-defect (sulfur vacancy) dominated growth with a change in the sulfur concentration with time. This may be accompanied by a core–shell growth of the flake . Therefore, the WS 2 flake consists of defect domains indicated by the flat topography and the change in PL- and Raman-intensity as well as the peak position shift of the vibrational modes. − , Hence, the defects determine the optical and electronic properties of the flake, and a lattice mismatch induced strain appears between these domains …”

“…Increasing the exposure time of the flake to the sulfur leads to larger flakes. In general, the formation of the WS 2 crystals is quite complex and depends additionally on the generation of defects and lattice mismatches, which results in a core–shell growth , and screw dislocation. , In addition, hexagonally shaped flakes with a heterostructure of sulfur- and tungsten vacancies were reported. − Those vacancies were revealed by PL and Raman spectroscopy or labeling with a fluorophore . The understanding of the formation of such peculiar structures is therefore critical for the future application of these materials.…”

“…32 Increasing the exposure time of the flake to the sulfur leads to larger flakes. In general, the formation of the WS 2 crystals is quite complex and depends additionally on the generation of defects and lattice mismatches, which results in a core−shell growth 25,33 and screw dislocation. 34,35 In addition, hexagonally shaped flakes with a heterostructure of sulfur-and tungsten vacancies were reported.…”

Hybrid Metasurfaces of Plasmonic Lattices and 2D Materials

“…[143] 2D materials exhibit highly tunable optical properties achieved via the control of layers number, strain, chemical doping, alloying, intercalation, heterostructure, substrate engineering, and external electric field. [144][145][146][147][148][149][150] For example, 2D materials show large (several orders of magnitude larger than the conventional semiconductors) and ultrafast nonlinear optical (NLO) response, broadband and tunable optical absorption, ultrafast recovery time, and large optical and thermal damage threshold. [151][152][153][154] These nonlinear properties have been successfully employed in demonstrations of all-optical modulators, saturable absorbers for passive mode locking lasing, Q-switching, wavelength converters, and optical limiters.…”

Enhanced visible-light-driven photocatalytic activity in SiPGaS/arsenene-based van der Waals heterostructures

“… 6 Additionally, to bolster water splitting efficiency, a high absorption coefficient (preferably within the visible range), high charge carrier mobility, and effective conversion of solar energy are crucial parameters to be met. 7 Two-dimensional (2D) layered materials have garnered extensive research attention due to their wide-ranging applications, including photocatalysis, 8 , 9 optoelectronics, 10 , 11 , 12 , 13 and spintronics. 14 , 15 , 16 , 17 However, these materials encounter inherent limitations, such as pronounced excitonic effects and large effective mass, which contribute to the rapid recombination of photoexcited charge carriers.…”