Nanoscrolls of Janus Monolayer Transition Metal Dichalcogenides

Abstract

Tubular structures of transition metal dichalcogenides (TMDCs) have attracted attention in recent years due to their emergent physical properties, such as the giant bulk photovoltaic effect and chirality-dependent superconductivity. To understand and control these properties, it is highly desirable to develop a sophisticated method to fabricate TMDC tubular structures with smaller diameters and a more uniform crystalline orientation. For this purpose, the rolling up of TMDC monolayers into nanoscrolls is an attractive approach to fabricating such a tubular structure. However, the symmetric atomic arrangement of a monolayer TMDC generally makes its tubular structure energetically unstable due to considerable lattice strain in curved monolayers. Here, we report the fabrication of narrow nanoscrolls by using Janus TMDC monolayers, which have an out-of-plane asymmetric structure. Janus WSSe and MoSSe monolayers were prepared by the plasma-assisted surface atom substitution of WSe2 and MoSe2 monolayers, respectively, and then were rolled by solution treatment. The multilayer tubular structures of Janus nanoscrolls were revealed by scanning transmission electron microscopy observations. Atomic resolution elemental analysis confirmed that the Janus monolayers were rolled up with the Se-side surface on the outside. We found that the present nanoscrolls have the smallest diameter of about 5 nm, which is almost the same as the value predicted by the DFT calculation. The difference in work functions between the S- and Se-side surfaces was measured by Kelvin probe force microscopy, which is in good agreement with the theoretical prediction. Strong interlayer interactions and anisotropic optical responses of the Janus nanoscrolls were also revealed by Raman and photoluminescence spectroscopy.

Bending Direction-Related Anisotropic Transport Characteristics of Two-Dimensional Janus MoSSe Devices

“…Its unique three-layer atomic structure provides a platform for the stacking of different atoms, which results in a variety of polymorphic structural phases with different properties, including the 2H phase for semiconductors, the 1T phase for metals, and the lattice-distorted 1T′ phase . MoSSe exhibits a longer exciton lifetime, greater basal hydrogen evolution reaction catalytic activity, a piezoelectric coefficient that can be compared with conventional TMDs semiconductors, and higher carrier mobility. − The carrier mobility of electrons and holes in the armchair direction of the 2D Janus MoSSe can reach 52.72 and 210.95 cm 2 V –1 s –1 . Janus MoSSe has a curl rate of 0.178 nm –1 .…”

Centrifugal Force-Assisted Preparation of Closely Packed Transition Metal Dichalcogenide Nanoscrolls for Enhanced Optoelectronic Performance

“…A number of methods have been developed for fabricating TMDC nanoscrolls, such as volatile organic solvent evaporation, ,,,− etching the supported substrate by alkali solution, ,,, dragging a water droplet across a heated TMDC nanosheet, self-assembly of amine-functional amphiphilic molecules, , supercritical fluid processing, and shear flow-assisted scrolling in a microfluidic platform. , How to curl the edge of a nanosheet and then form a nanoscroll spontaneously with the aid of an external stimulus is the driving force for rolling up the TMDC nanosheet. During the evaporation process of a volatile organic solvent, the surface tension gradient near the contact line can induce fluid flow, which rolls up the edge of the TMDC nanosheet until a nanoscroll is formed.…”