Nanomechanical Characterisation of Two - Dimensional Layered Materials

Nanomechanical Characterisation of Two-Dimensional Layered Materials [2012]

 

 

We report the first example of a 2-D inorganic-organic (hybrid) framework material bonded by weak van der Waals interactions, which can be ultrasonically exfoliated into nanosheets.

The fully exfoliated nanosheets correspond to a unilamellar thickness of ~1 nm, while the partially exfoliated multilayer films exhibit a typical thickness on the order of 10 nm. It can be seen that such a colloidal suspension exhibits the Tyndall effect (Figure), whereby the finely dispersed nanosheets in solution are capable of scattering an incident laser light beam.

We used atomic force microscopy to characterize their surface topography and to map the variation of nano-mechanical properties across the surface of the delaminated nanosheets. The morphology and crystallographic orientation of the exfoliated layers were further studied by transmission electron microscopy. Additionally, we investigated the elastic anisotropy underlying the bulk host material by means of nanoindentation performed on single crystals, from which the critical resolved shear stress needed for micromechanical delamination of individual layers was determined to be relatively small (ca. 0.4 GPa).

Nanosheets generated by such a "top-down" approach are extremely promising because they can be used as precursors for creating continuous thin films, or to be further integrated with various polymer matrices to afford multi-functional composite materials.