Compressive behavior of crystalline nanoparticles with atomic-scale surface steps

Atomic-scale surface steps play an important role in the mechanical behaviors of nanoparticles. Both molecular dynamics and finite element simulations are performed to investigate the elastic compression of copper nanoparticles. When surface steps are taken into account, the finite element calculation predicts the same compressive load-depth relation as the atomistic simulation. It is revealed that the compression of crystalline nanoparticles on facets should be characterized by a flat punch indenting an elastic half space, instead of the widely adopted Hertzian model with smooth spherical surface. As the particle size increases from nanometers to microns, the influence of atomic-scale surface steps becomes insignificant and the compressive load-depth relation transmits from the flat punch model to the Hertzian model. This study bridges the contact of an individual particle from nanoscale to microscale, and is helpful for using the indentation technique to measure the mechanical properties of particles.