Mechanical Properties of Amorphous Silicon Nanoparticles

Abstract

The compression of amorphous silicon nanoparticles is investigated by means of molecular dynamics simulations, at two temperatures and for diameters equal to 16 nm and 34 nm. The nanoparticles deform plastically, with maximum contact stresses in the range 8.5-11 GPa, corresponding to strains between 12% and 24%. No clear size effect is observed. Despite large contact stress values, the formation of high density crystalline or amorphous phases is not observed, presumably due to the presence of lateral free surfaces allowing for plasticity deconfinement. Atomic displacements analysis confirms that during plastic deformation, atoms close to indenters are first pushed towards the nanoparticle center, before migrating laterally towards free surfaces. Plastic deformation leads to an increase of fivefold coordinated atoms, which are spatially correlated with the largest atomic displacements.

Modeling the mechanical properties of nanoparticles: a review

“…They also show that the deformation becomes more homogeneous as the NP size decreases (Figure 11). A seemingly opposite behavior is observed for a-Si NPs [159]. The compression yields an increase of 5-fold coordinated atoms, which are the main carriers for plastic deformation in amorphous silicon [165].…”

“…The influence of cross-linking between the hydrocarbonated molecules constituting the soot was also recently put forward [163]. Conversely, for an already dense material like amorphous silicon, only a 2% density increase at a compression strain of 0.3 is observed [159]. In the latter case, the matter pushed by the flat-punch indenter tends to flow and escape from the sides.…”

“…The compression yields an increase of 5-fold coordinated atoms, which are the main carriers for plastic deformation in amorphous silicon [165]. However, those appear to be homogeneously distributed in the NP, with no influence of the NP size [159]. Furthermore, plastic deformation proceeds without the formation of localized shear bands, unlike in bulk amorphous silicon [166].…”

“…These studies revealed several interesting and sometimes apparently contradictory features. For instance, Kilymis and co-workers investigated the mechanical properties of amorphous silicon NPs with two different diameters, 16 nm and 34 nm, averaged over 5 configurations for each size [159]. They found a maximum stress reduction of about 5-6% from large to small NPs, for two different temperatures i.e., smaller is softer, unlike for crystalline materials.…”