Surface Properties of Laser-Treated Molybdenum Disulfide Nanosheets for Optoelectronic Applications

Abstract

Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS in both ambient and vacuum conditions via confocal μ-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS, which leads to etching and redeposition of amorphous MoS on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS nanosheets exhibit under high incident laser power for future optoelectronic applications.

Layer-by-layer thinning of MoS2 via laser irradiation

“…The systematic investigation of MoS 2 laser thinning presented herein enables a mechanistic understanding of the etching process. The results demonstrate the presence of nanoparticles on the MoS 2 at sufficient laser treatment conditions prior to layer-by-layer thinning; previous work submits that the nanoparticles are due to the oxidation, etching, and redeposition of the MoS 2 [39,40]. It is hypothesized here that the nanoparticles act as nucleation sites for the subsequent layer-by-layer thinning.…”

Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers

“…Alrasheed et al [146] used a 532 nm laser to irradiate mechanically exfoliated MoS 2 few-layers (less than 5 layers) on SiO 2 /Si substrates. The power ranged between 0.93 and 8.3 mW and the treatment time was 0.01-180 s. In ambient conditions, MoS 2 nanosheets were etched and amorphous MoS 2 redeposited on the nanosheets at low laser powers while the few-layers were oxidized and MoS 2 nanoparticles formed at high laser powers.…”

“…Interfaces 2018, 10, 18104−1811218108 Raman intensity and linewidth (FWHM) of (a) mono-layer-ed (1L), (b) tri-layer-ed (3L), and (c) 5-layer-ed (5L) MoS 2 nanosheets laser-treated in ambient conditions. Reprinted with permission from Reference[146]. Copyright c 2018 American Chemical Society.…”

Room temperature wideband tunable photoluminescence of pulsed thermally annealed layered black phosphorus

“…For each different emission wavelength, there is a corresponding P (2p) processed image representative of the black phosphorus feature centered at ≈129 eV (center column). A set of masks was created in a manner consistent with previous work [5] to define the edge of each nanosheet as illustrated in Figure S9, and spectra associated with pixels inside these regions of interest were assembled from the raw image stack, as shown in the right column. We observe from the extracted P (2p) spectrum that the native black phosphorus (P BP ) was characterized by a broad feature at ≈129 eV for the 2p 3/2 component, consisting of >97% of the total phosphorus species on the surface.…”

“…New emerging two-dimensional (2D) materials have attracted significant attention in recent years due to their extraordinary mechanical, electrical, and optical properties at the nanoscale [1][2][3][4][5]. Among these materials, layered black phosphorus has played a key role in several applications.…”