Kovalenko, PhD candidate.
Department of Material Science and Engineering, Technion – Israeli institute of Technology, 32000 Haifa, Israel
The Winterbottom analysis  of the equilibrated particles on substrate provides direct experimental access to the determining of the interface and anisotropic surface energies of solids. Yet, the kinetic limitation on the shape-changing surface diffusion on the singular flat facets results in stability of non-equilibrium crystal shapes even for high homologous temperatures and small crystal sizes . To overcome this limitation, we developed a new technique for equilibration of faceted sub-micrometer sized particles on sapphire substrate obtained by solid state agglomeration (dewetting). The method relies on crystalline defects introduced in the particles. We employed the atomic force microscopy (AFM)-based indentation/tapping by hard diamond tip, and the scratching of the sample surface to introduce the plastic strain in the particles. The shape of deformed particles evolved towards equilibrium after subsequent heat treatments, whereas the pristine anisotropic particles preserved their original non-equilibrium shape. Tracking the shape changes of the deformed particles with the aid of AFM and scanning electron microscopy (SEM) allowed identifying the statistically-significant population of fully equilibrated particles suitable for the surface/interface energies measurements. We also identified the window of annealing parameters for which the deformed anisotropic gold particles exhibited the shape memory effect.
The application of the developed method to the molybdenum particles opened the route for the production of the equilibrated crystals suitable for the nanomechanical compression testing. The elastic deformation up to the stress levels comparable to the theoretical strength of Mo was followed by the catastrophic plastic collapse. We found that the deformation size effect strongly depends on the crystal shape and the test geometry.
Supervisor: Prof. E. Rabkin