Michael Asoro is a Ph.D. candidate in his fifth year working under the co-supervision of Dr. Paulo Ferreira and Dr. Desiderio Kovar. Michael’s research focuses on coalescence and sintering in metallic nanoparticles.
Nanoparticles possess unique physical, chemical, optical and electronic properties stemming from their nanoscale dimensions and are currently used in catalysis, microelectronics, drug delivery etc. However, during processing or usage, nanoparticles have a strong tendency to agglomerate and coalesce over short time scales, even at room temperature, which lead to significant changes in behavior and performance. In some applications, such as catalysis, coalescence is detrimental as it leads to a reduction in catalytic activity. In other situations, as for example in the fabrication of thick film conductors, the ability to enhance sintering is critical to producing high conductivity lines at low temperatures and would, therefore open the door to the development of many novel devices.
The primary objective of Michael’s research is to determine how particle size, temperature and surfactants influence sintering in FCC metallic nanoparticles, using in-situ transmission electron microscopy (TEM) heating. With his group, Michael is, for the first time, making direct, real-time measurements of nanoparticle size, neck growth, dihedral angle and grain boundary motion during sintering. These values are then used to calculate fundamental material transport parameters, such as surface diffusivity and grain boundary mobility, which are important for understanding sintering at the nanoscale. In-situ TEM experiments provide critical and valuable real time dynamic information for direct investigation of the link between the evolution of sintering and controlling mechanisms, which conventional experiments such as post-mortem TEM observations are not capable of conveying.
Fig. 1: A sequence of aberration-corrected HAADF STEM images showing the coalescence of platinum nanoparticles under the influence of the electron beam at ambient temperature. In addition to the platinum nanoparticles, individual platinum atoms and platinum clusters can also be observed on the carbon support.
[M. A. Asoro, D. Kovar, Y. Shao-Horn, L. F. Allard, P. J. Ferreira, Nanotechnology 21 (2010) 025701]