  Semiconducting monolayer of 2D material are able to concatenate multiple
interesting properties into a single component. Here, by combining
opto-mechanical and electronic measurements, we demonstrate the presence of a
partial 2H-1T phase transition in a suspended 2D monolayer membrane of MoS2.
Electronic transport shows unexpected memristive properties in the MoS2
membrane, in the absence of any external dopants. A strong mechanical softening
of the membrane is measured concurrently and may only be related to the phase
2H-1T phase transition which imposes a 3percent directional elongation of the
topological 1T phase with respect to the semiconducting 2H. We note that only a
few percent 2H- 1T phase switching is sufficient to observe measurable
memristive effects. Our experimental results combined with First-principles
total energy calculations indicate that sulfur vacancy diffusion plays a key
role in the initial nucleation of the phase transition. Our study clearly shows
that nanomechanics represents an ultrasensitive technique to probe the crystal
phase transition in 2D materials or thin membranes. Finally, a better control
of the microscopic mechanisms responsible for the observed memristive effect in
MoS2 is important for the implementation of future devices.
