  Mechanical properties of transition metal dichalcogenides (TMDCs) are
relevant to their prospective applications in flexible electronics. So far, the
focus has been on the semiconducting TMDCs, mostly MoX2 and WX2 (X=S, Se) due
to their potential in optoelectronics. A comprehensive understanding of the
elastic properties of metallic TMDCs is needed to complement the semiconducting
TMDCs in flexible optoelectronics. Thus, mechanical testing of metallic TMDCs
is pertinent to the realization of the applications. Here, we report on the
atomic force microscopy-based nano-indentation measurements on ultra-thin
2H-TaS2 crystals to elucidate the stretching and breaking of the metallic
TMDCs. We explored the elastic properties of 2H-TaS2 at different thicknesses
ranging from 3.5 nm to 12.6 nm and find that the Young's modulus is independent
of the thickness at a value of 85.9 +- 10.6 GPa, which is lower than the
semiconducting TMDCs reported so far. We determined the breaking strength as
5.07 4- 0.10 GPa which is 6% of the Young's modulus. This value is comparable
to that of other TMDCs. We used ab initio calculations to provide an insight to
the high elasticity measured in 2H-TaS2. We also performed measurements on a
small number of 1T-TaTe2, 3R-NbS2 and 1T-NbTe2 samples and extended our ab
initio calculations to these materials to gain a deeper understanding on the
elastic and breaking properties of metallic TMDCs. This work illustrates that
the studied metallic TMDCs are suitable candidates to be used as additives in
composites as functional and structural elements and for flexible conductive
electronic devices.
