Fracturing of polycrystalline MoS$_2$ nanofilms

TL;DR

This study investigates the fracture behavior of polycrystalline MoS2 nanofilms, revealing how electron beam irradiation can enhance their strain tolerance and providing insights for flexible electronics fabrication.

Contribution

It introduces a method to increase the critical strain of MoS2 films via electron beam irradiation and analyzes crack propagation along grain boundaries at the nanoscale.

Findings

Critical uniaxial strain is approximately 5%.

Electron beam irradiation increases critical strain beyond 10%.

Cracks propagate along grain boundaries and through grains.

Abstract

The possibility of tailoring the critical strain of 2D materials will be crucial for the fabrication of flexible devices. In this paper, the fracture in polycrystalline MoS2 films with two different grain orientations is studied at the micro- and nanoscale using electron microscopy. The critical uniaxial strain is determined to be approximately 5% and independent of the sample morphology. However, electron beam irradiation is found to enhance the interaction between the MoS2 and the PDMS substrates, leading to an increased critical strain that can exceed 10%. This enhancement of strain resistance was used to fabricate a mechanically robust array of lines 1 mm in length. Finally, nanoscale crack propagation studied by transmission electron microscopy showed that cracks propagate along the grain boundaries as well as through the grains, preferentially along van der Waals bonding. These results provide insight regarding the fracture of polycrystalline 2D materials and a new method to tailor the critical strain and nanofabrication of ultra-thin MoS2 devices using well-developed tools, which will be of great interest to the flexible electronics industry.