Layer-by-layer thinning of MoS₂ via laser irradiation

Abstract

Layer-by-layer thinning of molybdenum disulfide (MoS 2) via laser irradiation was examined using Raman spectroscopy and atomic force microscopy. In particular, the effects of number of layers, laser conditions, and substrate were systematically identified. The results demonstrated the presence of nanoparticles on the MoS 2 at sufficient laser treatment conditions prior to layerby-layer thinning. The volume of nanoparticles was found to increase and then decrease as the number of MoS 2 layers increased; the non-monotonic trend was ascribed to changes in the thermal conductivity of the film and interfacial thermal conductance between the film and substrate with number of layers. Moreover, the volume of nanoparticles was found to increase as the magnification of the objective lens decreased and as laser power and exposure time increased, which was attributed to changes in the power density with laser conditions. The effect of substrate on nanoparticle formation and layer-by-layer thinning was investigated through a comparison of freestanding and substrate-supported MoS 2 subjected to laser irradiation; it was illustrated that freestanding films were thinned at lower laser powers than substrate-supported films, which highlighted the function of the substrate as a heat sink. For conditions that elicited thinning, it was shown that the thinned areas exhibited triangular shapes, which suggested anisotropic etching behavior where the lattice of the basal plane was preferentially thinned along the zigzag direction terminated by an Moor S-edge. High-resolution transmission electron microscopy of freestanding MoS 2 revealed the presence of a 2 nm thick amorphous region around the laser-treated region, which suggested that the crystalline structure of laser-treated MoS 2 remained largely intact after the thinning process. In all, the conclusions from this work provide useful insight into the progression of laser thinning of MoS 2 , thereby enabling more effective methods for the development of MoS 2 devices via laser irradiation.

Patterning GaSe by High-Powered Laser Beams

“…The DFM results show lower mobility of nanoparticles reflected by a decrease in image contrast (see Figure ). It is worth noticing that the nanoparticle formation after high-power laser processing could be a general observation in 2D semiconductors, like that reported for the laser thinning of the MoS 2 layers Figure b shows a new peak observed during the Raman line scan experiment that belongs to Ga 2 Se 3 .…”

“…Nanoparticle formation by laser irradiation was also previously reported for the case of laser-thinned MoS 2 films. The nanoparticles acted as nucleation sites, with size and distribution reported to depend on layer thickness and power density . Similar phenomena of nanoparticle formation were observed upon laser ablation of metallic layers, especially in liquid environments. , Raman spectroscopy, atomic force microscopy (AFM), dielectric force microscopy (DFM), and scanning electron microscopy (SEM) results showed that the nanoparticles formed remain to a large extent GaSe.…”

“…We hypothesize that melting and recrystallization of GaSe along the laser-irradiated edge occur as a consequence of photothermal heating. Meanwhile, photothermal effects from laser irradiation were also used for thinning 2D materials like MoS 2 . Laser-thinning multilayered graphene enabled single-layers without chemical transformation under ambient conditions thanks to optical interference and localized heat-dissipation mediated by the SiO 2 substrate showing the impact of photothermal heating in 2D materials .…”

Low‐Damaged Layer‐by‐Layer Etching of Large‐Area Molybdenum Disulfide Films via Mild Plasma Treatment

“…There have been various methodologies to control MoS 2 layer, such as laser irradiation, thermal annealing, and plasma etching treatment. [ 9–12 ] Castellanos‐Gomez et al. used laser irradiation to control the number of layers of mechanically exfoliated MoS 2 flakes.…”

“…[ 9 ] However, it is incompatible for patterned large‐scale MoS 2 or nanopatterned one, owing to its thermal ablation effect. [ 9,10 ] Alternatively, the plasma etching treatment is an efficient way to control MoS 2 layer because of its good selectivity, scalability, and relatively shorter processing time below 10 min. [ 12,13 ] Liu et al.…”