Wrapping Plasmonic Silver Nanoparticles inside One-Dimensional Nanoscrolls of Transition-Metal Dichalcogenides for Enhanced Photoresponse.

The low light absorption of transition-metal dichalcogenide (TMDC) nanosheets hinders their application as high-performance optoelectronic devices. Rolling them up into one-dimensional (1D) nanoscrolls and decorating them with plasmonic nanoparticles (NPs) are both effective strategies for enhancing their performance. When these two approaches are combined, in this work, the light-matter interaction in TMDC nanosheets is greatly improved by encapsulating silver nanoparticles (Ag NPs) in TMDC nanoscrolls. After the silver nitrate (AgNO3) solution was spin-coated on monolayer (1L) MoS2 and WS2 nanosheets grown by chemical vapor deposition, Ag NPs were homogeneously formed to obtain MoS2-Ag and WS2-Ag nanosheets due to the TMDC-assisted spontaneous reduction, and their size and density can be well controlled by tuning the concentration of the AgNO3 solution. By the simple placement of alkaline droplets on MoS2-Ag or WS2-Ag hybrid nanosheets, MoS2-Ag or WS2-Ag nanoscrolls with large sizes were obtained in large area. The obtained hybrid nanoscrolls exhibited up to 500 times increased photosensitivities compared with 1L MoS2 nanosheets, arising from the localized surface plasmon resonance effect of Ag NPs and the scrolled-nanosheet structure. Our work provides a reliable method for the facile and large-area preparation of NP/nanosheet hybrid nanoscrolls and demonstrates their great potential for high-performance optoelectronic devices.

Transforming Monolayer Transition-Metal Dichalcogenide Nanosheets into One-Dimensional Nanoscrolls with High Photosensitivity.

One-dimensional (1D) nanoscrolls derived from two-dimensional (2D) nanosheets own unusual physical and chemical properties that arise from the spiraled 1D morphology and the atomic thin 2D building blocks. Unfortunately, preparation of large-sized nanoscrolls of transition-metal dichalcogenides (TMDCs) remains a big challenge, which greatly restricts the fabrication of single-scroll devices for their fundamental studies and further applications. In this work, we report a universal and facile method, by making use of the evaporation process of volatile organic solvent, to prepare TMDC (e.g., MoS2 and WS2) nanoscrolls with lengths of several tens to one hundred micrometers from their 2D precursors presynthesized by chemical vapor deposition on Si/SiO2. Both atomic force microscopy and electron microscopy characterizations confirmed the spirally rolledup structure in the resulting nanoscrolls. An interlayer spacing of as small as ∼0.65 nm was observed, suggesting the strong coupling between adjacent layers, which was further evidenced by the emergence of new breathing mode peaks in the ultralow frequency Raman spectrum. Importantly, compared with the photodetector fabricated from a monolayer MoS2 or WS2 nanosheet, the device based on an MoS2 or WS2 nanoscroll showed the much enhanced performance, respectively, with the photosensitivity greatly increased up to 2 orders of magnitude. Our work suggests that turning 2D TMDCs into 1D scrolls is promising in achieving high performances in various electronic/optoelectronic applications, and our general method can be extended to the preparation of large-sized nanoscrolls of other kinds of 2D materials that may bring about new properties and phenomena.