Shape control of size-selected naked platinum nanocrystals

Controlled growth of far-from-equilibrium-shaped nanoparticles with size selection is essential for the exploration of their unique physical and chemical properties. Shape control by wet-chemistry preparation methods produces surfactant-covered surfaces with limited understanding due to the complexity of the processes involved. Here, we report the controlled production and transformation of octahedra to tetrahedra of size-selected platinum nanocrystals with clean surfaces in an inert gas environment. Molecular dynamics simulations of the growth reveal the key symmetry-breaking atomic mechanism for this autocatalytic shape transformation, confirming the experimental conditions required. In-situ heating experiments demonstrate the relative stability of both octahedral and tetrahedral Pt nanocrystals at least up to 700 degrees C and that the extended surface diffusion at higher temperature transforms the nanocrystals into equilibrium shape. Tetrahedral nanocrystals are out-of-equilibrium structures whose growth mechanism is a long-standing open problem. Here, the authors show that pure Pt tetrahedral nanocrystals grow in the gas phase and single out the defect-mediated mechanism leading to the symmetry-breaking for tetrahedral growth.

Automated summary

This study reports the controlled production and transformation of platinum nanocrystals from octahedra to tetrahedra in an inert gas environment. Molecular dynamics simulations revealed the symmetry-breaking atomic mechanism for this shape transformation, and in-situ heating experiments demonstrated the relative stability of both structures at least up to 700 degrees C. Tetrahedral nanocrystals are out-of-equilibrium structures with a growth mechanism that is still an open problem, but the authors identified a defect-mediated mechanism for tetrahedral growth.