  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.
