Long-Term Exposure of MoS2 to Oxygen and Water Promoted Armchair-to-Zigzag-Directional Line Unzippings

Abstract

Understanding the long-term stability of MoS2 is important for various optoelectronic applications. Herein, we show that the long-term exposure to an oxygen atmosphere for up to a few months results in zigzag (zz)-directional line unzipping of the MoS2 basal plane. In contrast to exposure to dry or humid N2 atmospheres, dry O2 treatment promotes the initial formation of line defects, mainly along the armchair (ac) direction, and humid O2 treatment further promotes ac line unzipping near edges. Further incubation of MoS2 for a few months in an O2 atmosphere results in massive zz-directional line unzipping. The photoluminescence and the strain-doping plot based on two prominent bands in the Raman spectrum show that, in contrast to dry-N2-treated MoS2, the O2-treated MoS2 primarily exhibits hole doping, whereas humid-O2-treated MoS2 mainly exists in a neutral charge state with tension. This study provides a guideline for MoS2 preservation and a further method for generating controlled defects.

Scattering Properties of MoS2 Edges and Folds Using Darkfield Hyperspectral Microscopy

“…The scattering image, illuminated at each excitation wavelength (λ), is captured by a CCD camera through a dark-field lens that selectively collects scattering light while rejecting reflected light. Figure B presents a schematic representation of an image stack that features a triangular MoS 2 grain on a quartz substrate, obtained by dry transfer of the synthesized grain using the conventional chemical vapor deposition (CVD) method as outlined in our previous reports , (Methods). The image stack (see the movie), which combines images excited at each λ ranging from 430 to 800 nm, contains both spatial and spectral information.…”

“…After the furnace temperature reached 750 °C, the crucible was kept at 750 °C for 20 min and then cooled under the argon flow until the temperature reached 100 °C (20 min). The growth of MoS 2 was achieved using the previously developed method , involving the CVD method with spin-coated MoO 3 and S as precursors [Figure S1A and S1B for the CVD apparatus and the schematic of CVD growth, respectively]. Optical images (Figure S1C–S1D) reveal that most of the MoS 2 formed has a triangular shape, showing an average size of 12 μm 2 (Figure S1E).…”

“…Additionally, the scattering spectra of folds, which are The growth of MoS 2 was carried out with two precursors (e.g., MoO 3 and S) using an atmospheric hot-walled CVD setup according to the previous reports. 29,34,35 The surface of the SC-MoO 3 coated piece was placed face-up in a hot zone of a quartz tube in a hot-wall furnace (Lindberg Blue-M, Thermo Scientific). The alumina crucible containing 200 mg of sulfur was placed 16 cm upstream of the hot zone to maintain a temperature of 250 °C during growth temperature.…”

Hierarchical van der Waals Heterostructure Strategy to Form Stable Transition Metal Dichalcogenide Dispersions

“…Micro Raman measurements were conducted using a custom-made instrument equipped with a 532 nm laser (Cobolt 08-DPL, Hubner Photonics) via a backscattering geometry according to the previous literature. − Briefly, inelastic scattering signals from the focused laser spot on the sample were collected via an objective lens (50× or 100×, Plan, Olympus, Japan) in an upright microscope (BX51, Olympus, Japan). The collected scattering was focused via a tube lens in a trinocular of the microscope and dispersed and recorded with a spectrometer (Triax320, Horiba, Japan) with 1800 g/mm (resolution < 1 cm –1 ) and a charge-coupled device detector (Synergy, Horiba, Japan).…”