Solvent-Free Preparation of Closely Packed MoS₂ Nanoscrolls for Improved Photosensitivity

Abstract

Due to their enhanced light absorption efficiency, one-dimensional (1D) transition metal dichalcogenide (TMDC) nanoscrolls derived from two-dimensional (2D) TMDC nanosheets have shown excellent optoelectronic properties. Currently, organic solvent and alkaline droplet-assisted scrolling methods are popular for preparing TMDC nanoscrolls. Unfortunately, the adsorption of organic solvent or alkaline impurities on TMDC is inevitable during the preparation, which affects the optoelectronic properties of TMDC. In this work, we report a solvent-free method to prepare closely packed MoS 2 nanoscrolls by dragging a deionized water droplet onto the chemical vapor deposition grown monolayer MoS 2 nanosheets at 100 °C (referred to as MoS 2 NS-W). The as-prepared MoS 2 NS-W was well characterized by optical microscopy, atomic force microscopy, and ultralow frequency (ULF) Raman spectroscopy. After high temperature annealing, the height of MoS 2 nanoscrolls prepared using an ethanol droplet (referred to as MoS 2 NS-E) greatly decreased, indicating the loss of encapsulated ethanol in MoS 2 NS-E. While the height of MoS 2 NS-W was almost unchanged under the same conditions, implying that no water was embedded in the scroll. Compared to the MoS 2 NS-E, the MoS 2 NS-W shows more ULF breathing mode peaks, confirming the stronger interlayer interaction. In addition, the MoS 2 NS-W shows a higher Young's modulus than MoS 2 NS-E, which could arise from the closely packed scroll structure. Importantly, the MoS 2 NS-W device showed a photosensitivity 1 order of magnitude higher than that of the MoS 2 NS-E device under blue, green, and red lasers, respectively. The decreased photosensitivity of MoS 2 NS-E was attributed to the larger dark current, which might be assigned to the adsorbed ethanol between the adjacent layers in MoS 2 NS-E. Our work provides a solvent-free method to prepare closely packed MoS 2 nanoscrolls at large scale and demonstrates their great potential for high-performance optoelectronic devices.

Recent Advances in Rolling 2D TMDs Nanosheets into 1D TMDs Nanotubes/Nanoscrolls

“…Organic solvents or alkaline contaminants unfortunately adsorb on TMD during manufacturing, which affects its optoelectronic properties. A solvent-free method for producing densely packed MoS 2 NSs at 100 °C was presented, which involved dragging a deionized water droplet atop 1L-MoS 2 nanosheets generated by CVD, which are referred to as MoS 2 NS-W. [125] The as-prepared MoS 2 NS-W was examined using optical microscopy, atomic force microscopy (AFM), and Raman spectroscopy with ultralow frequency. The height of MoS 2 NSs generated with an ethanol droplet, which is referred to as MoS 2 NS-E, decreased dramatically, which revealed the loss of encapsulated ethanol in MoS 2 NS-E after high-temperature annealing.…”

“…h) Graphs of the photocurrentto-dark-current ratio of an MoS 2 nanosheet and NS photodetectors. Panels (a-h) were reproduced with permission [125]. Copyright 2022, American Chemical Society.…”

Emerging Nonplanar van der Waals Nanoarchitectures from 2D Allotropes for Optoelectronics

“…[ 26,37 ] A heating process would effectively weaken the adhesion between substrate and vdWLs. [ 17,38 ] At the same time, the vdWLs are curled and rolled up by the released built‐in strain induced by thermal mismatch (Figure 2b) [ 17 ] during the continued liquid penetration until the nanoscrolls are fully formed (Figure 2a). In the whole process of self‐assembly, solid–liquid interfacial energy γ sl , a dependent variable with the ratio of organics to water, is a crucial factor affecting the difficulty of liquid intercalation that could be written as Young's equation $$\[ \begin{array}{*{20}{c}}{{\gamma _{sl}} = {\gamma _{sg}} - {\gamma _{\lg }}\cos {\theta _{\rm{c}}}}\end{array} \]$$where γ sg and γ lg are the solid–gas and liquid–gas interfacial energies, respectively, and θ c is equilibrium contact angle.…”

“…Therefore, the cosolvent concentration needs to be selected within a moderate range to create cleaner vdW interfaces for better device performance. [ 38 ]…”

Decorating MoS2 Nanoscrolls with Solution-Processed PbI2 Nanocrystals for Improved Photosensitivity

“…In recent years, it has been reported that the optoelectronic performance of TMDC nanosheets can also be greatly enhanced by transforming the monolayer TMDC nanosheet into a one-dimensional (1D) spiral scroll. − The TMDC nanoscroll not only retains the excellent properties of monolayer TMDC nanosheets but also exhibits unique properties because of its helical 1D structure. For instance, the photosensitivity of a MoS 2 nanoscroll is around 2 orders of magnitude higher than that of a monolayer MoS 2 nanosheet .…”