Mechanical Reshaping of Inorganic Nanostructures with Weak Nanoscale Forces

Abstract

Inorganic nanomaterials are often depicted as rigid structures whose shape is permanent. However, forces that are ordinarily considered weak can exert sufficient stress at the nanoscale to drive mechanical deformation. Here, we leverage van der Waals (VdW) interactions to mechanically reshape inorganic nanostructures from planar to curvilinear. Modified plate deformation theory shows that high-aspect-ratio two-dimensional particles can be plastically deformed via VdW forces. Informed by this finding, silver nanoplates were deformed over spherical iron oxide template particles, resulting in distinctive bend contour patterns in bright-field (BF) transmission electron microscopy (TEM) images. High-resolution TEM images of deformed areas reveal the presence of highly strained bonds in the material. Finally, we show that the distance between two nearby template particles allows for the engineering of several distinct curvilinear morphologies. This work challenges the traditional view of nanoparticles as static objects and introduces methods for postsynthetic mechanical shape control.

Curvature and self-assembly of semi-conducting nanoplatelets

“…This is the same order of magnitude as surface stresses measured on a gold cantilever imposed by a thiol ML 56 . These estimates are also consistent with a recent report showing that Ag nanoplates are significantly deformed by weak van der Waal forces 60 .…”

Multilayer Graphene—A Promising Electrode Material in Liquid Cell Electrochemistry

“…The symmetric appearance in postgrowth images (Figure 4e,f) suggest regions of mechanical strain as it is consistent with the distinctive bend contours seen when 2D materials are deformed over particles and curve due to van der Waals interactions. [ 53 ] We observe similar bend contours in graphene electrodes (Figure S8, Supporting Information), mainly when the graphene layer is thick (>30 layers) but much less commonly when it is thin. We speculate that defects in the 2D materials serve to preferentially nucleate metal nanocrystals that grow in liquid that has penetrated to the 2D material/SiN x interface, deforming the 2D layer.…”

Surface Ligands Dictate the Mechanical Properties of Inorganic Nanomaterials

“…These results are to be expected due to the trivial influence of the changing Hamaker constant on the overall van der Waals interaction, and small interaction area between the template particle and the nanoplate, respectively. 48 Since a larger bend contour size indicates a nanoplate with greater mechanical strength, we can conclude from these data that some property of the surface chemistry couples to the mechanical behavior of the inorganic particle. This observation is corroborated by AFM characterization, which illustrates topographically that the lateral extent of the bend contour is directly related to the ligand binding strength (Figure S7).…”

“…To gain further insight into how the shell atoms modulate the effective mechanical behavior of the entire nanostructure, we modified an analytical model developed in our previous work that compares the strain energy of a plate against its van der Waals attraction to a substrate . More specifically, a radially symmetric solution to the Kirchhoff–Love equations for the deformation of a plate was modified to account for both plastic deformation and a core–shell geometry (see Supporting Information); the core is assigned the bulk properties of Ag, and the shell has mechanical constants that are allowed to vary in order to match the observed bend contour dimensions.…”