Mrs. Mor Levi - Ph.D. Candidate
02/01/2025
אודיטוריום ע"ש דויד וואנג, בניין מידן, קומה 3
14:30
Solid-state dewetting is an efficient fabrication method of equilibrated nanoparticles of pure metals and metal alloys. Due to their defect-free nature, these nanoparticles exhibit unique properties such as high mechanical strength and extraordinary phase stability. We have selected the Nickel-Platinum system for this study because of its high relevance for heterogeneous catalysis. We employed solid-state dewetting to fabricate the Nickel-Platinum nanoparticles of variable size, shape, composition, and degree of atomic long-range ordering. The effect of these parameters on the mechanical properties of Ni-Pt nanoparticles was studied.
We observed morphological differences with the change in composition leading to lower and wider nanoparticles with the increasing Platinum content. A strong “size effect” on compressive strength has been observed as smaller nanoparticles exhibited higher strength. No significant effect of atomic ordering on the mechanical properties of the nanoparticles could be observed.
We also studied the ordering mechanisms in nearly stoichiometric NiPt nanoparticles and uncovered oscillatory cyclic-type changes in the fraction of disordered (100)-oriented nanoparticles, which were correlated with particle rotation and re-orientation. We related this unusual behavior to an interplay between the chemical energy and the strain energy within the nanoparticles, resulting in a nucleation of twinning dislocations and out-of-plane particle rotation. The discovery of ordering-induced particle rotation and reorientation introduces a novel approach to engineering.