  Two-dimensional Indium Selenide (InSe) has attracted extensive attention
recently due to its record-high charge carrier mobility and photoresponsivity
in the fields of electronics and optoelectronics. Nevertheless, the mechanical
properties of this material in the ultra-thin regime have not been investigated
yet. Here, we present our efforts to determine the Young's modulus of thin InSe
(~1-2 layers to ~40 layers) flakes experimentally by using buckling-based
methodology. We find that the Young's modulus has a value of 23.1 +- 5.2 GPa,
one of the lowest values reported up to date for crystalline two-dimensional
materials. This superior flexibility can be very attractive for different
applications, such as strain engineering and flexible electronics.
