Electromechanics in MoS2 and WS2: nanotubes vs. monolayers

TL;DR

This paper investigates the electromechanical properties of MoS2 and WS2 in nanotube form, revealing their strain-induced electronic transitions and demonstrating Raman spectroscopy as a tool for in situ strain monitoring.

Contribution

It provides the first theoretical analysis of large-diameter TMD nanotubes' electromechanical behavior, showing similar properties to monolayers and bulk materials, and highlights their potential for nanoelectromechanical applications.

Findings

Semiconductor-metal transition at 16% strain in TMD nanotubes.

MWNTs exhibit twice the conductance of SWNTs, with each wall contributing proportionally.

Raman spectroscopy effectively monitors strain in TMD nanotubes.

Abstract

The transition-metal dichalcogenides (TMD) MoS2 and WS2 show remarkable electromechanical properties. Strain modifies the direct band gap into an indirect one, and substantial strain even induces an semiconductor-metal transition. Providing strain through mechanical contacts is difficult for TMD monolayers, but state-of-the-art for TMD nanotubes. We show using density-functional theory that similar electromechanical properties as in monolayer and bulk TMDs are found for large diameter TMD single- (SWNT) and multi-walled nanotubes (MWNTs). The semiconductor-metal transition occurs at elongations of 16 %. We show that Raman spectroscopy is an excellent tool to determine the strain of the nanotubes and hence monitor the progress of that nanoelectromechanical experiment in situ. TMD MWNTs show twice the electric conductance compared to SWNTs, and each wall of the MWNTs contributes to the conductance proportional to its diameter.