Periodic Reporting for period 4 - CLUSTER (Birth of solids: atomic-scale processes in crystal nucleation)
Reporting period: 2020-12-01 to 2021-05-31
The importance of this project lies in the fact that we are continuously confronted with solid matter, but we still know very little about what triggers the crystallization of solid matter. Moreover, controlled crystallization reactions are important in various industrial areas, such as pharmaceutical, metallurgic, and, e.g. energy storage sectors. In this respect, shedding light on nucleation reactions might eventually enable engineering of nanomaterials, and potentially creating new materials of uncommon atomic order.
Within another approach aiming at shedding light on particle nucleation and growth, we investigate the formation of gold and silver particles in a liquid cell in (scanning) transmission electron microscopy (S/TEM). We employ the electron beam to trigger the reaction and are able to control growth mode and particle morphology by adjusting the electron dose. Moreover, exploring more complex reactions, we use silver nanoparticles as precursors for the growth of silver-gold core-shell particles. By carefully tuning electron dose and the local chemistry using surfactants and solvents, we succeeded to nucleate a continuous atomic layer of gold atoms on the surface of the Ag particles and thus extend liquid-cell reactions to form well defined core-shell Ag-Au nanoparticles. Being able to observe the actual nucleation process of the shell and maintain a controlled growth of the shell in an in-situ experiment in a liquid cell in the transmission electron microscope is new and reveals unprecedented control of such in-situ wet-chemical reactions.
Although atomic-resolution information is difficult to access with a conventional liquid cell in transmission electron microscopy, in another branch of research we explore the possibility of using window-free suspended ionic liquids to study reactions, particle nucleation and growth in liquid phase in S/TEM. Within this area of research we study the structure of tiniest Au and Pt clusters in ionic liquids and the formation and growth of nanoparticles at different temperatures.