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

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 MoS2 nanoscrolls by dragging a deionized water droplet onto the chemical vapor deposition grown monolayer MoS2 nanosheets at 100 °C (referred to as MoS2 NS-W). The as-prepared MoS2 NS-W was well characterized by optical microscopy, atomic force microscopy, and ultralow frequency (ULF) Raman spectroscopy. After high temperature annealing, the height of MoS2 nanoscrolls prepared using an ethanol droplet (referred to as MoS2 NS-E) greatly decreased, indicating the loss of encapsulated ethanol in MoS2 NS-E. While the height of MoS2 NS-W was almost unchanged under the same conditions, implying that no water was embedded in the scroll. Compared to the MoS2 NS-E, the MoS2 NS-W shows more ULF breathing mode peaks, confirming the stronger interlayer interaction. In addition, the MoS2 NS-W shows a higher Young's modulus than MoS2 NS-E, which could arise from the closely packed scroll structure. Importantly, the MoS2 NS-W device showed a photosensitivity 1 order of magnitude higher than that of the MoS2 NS-E device under blue, green, and red lasers, respectively. The decreased photosensitivity of MoS2 NS-E was attributed to the larger dark current, which might be assigned to the adsorbed ethanol between the adjacent layers in MoS2 NS-E. Our work provides a solvent-free method to prepare closely packed MoS2 nanoscrolls at large scale and demonstrates their great potential for high-performance optoelectronic devices.