| AVS 54th International Symposium | |
| In-situ Electron Microscopy Topical Conference | Monday Sessions |
| Session IE-MoM |
| Session: | Structure-Property Characterization |
| Presenter: | J.M. Howe, University of Virginia |
| Authors: | J.M. Howe, University of Virginia A.R.S. Gautam, University of Virginia S.K. Eswaramoorthy, University of Virginia |
| Correspondent: | Click to Email |
In-situ transmission electron microscopy (TEM) is an indispensable tool for determining the behavior of materials and interfaces under actual experimental conditions. This paper focuses on the results from in-situ heating experiments performed on nanoparticles in the TEM, using either high-resolution TEM (HRTEM) imaging or energy-dispersive X-ray spectroscopy (EDXS). Three different types of transformations and the fundamental processes associated with them are discussed. These include the atomic-level dynamics of an order-disorder interface near equilibrium in a Au-Cu alloy nanoparticle, the mechanisms of migration and coalescence of Au-Cu alloy nanoparticles supported on an amorphous-C thin-film, and the nucleation and growth behavior of phases and how elements partition between them in partially molten Al-Cu-Mg-Si nanoparticles in near-equilibrium and highly undercooled conditions. Some of the major results from these studies are summarized as follows. For the order-disorder interface near equilibrium in a Au-Cu alloy nanoparticle, it was found that both the interphase boundary position and thickness fluctuate with time and that the behavior of the disordered side of the interphase boundary differs from that of the ordered side. These features can be explained in terms of the physical properties of the different phases and the energetics of the interphase boundary. In the case of two Au-Cu alloy nanoparticles supported on an amorphous-C thin-film, it was found that Ostwald ripening and particle motion occur simultaneously, through collective surface fluctuations and a directed diffusional flux between the two particles. This flux becomes directly visible during coalescence, where redistribution of mass on the large particle is also revealed. In the partially molten Al-Si-Cu-Mg alloy nanoparticle, it was found that the solid Al phase is completely wet by the liquid and therefore cannot nucleate heterogeneously on the Si phase or oxide surface. Because heterogeneous nucleation is eliminated, it was possible to directly determine the metastable liquidus and solidus phase boundaries in the undercooled liquid by EDXS, in addition to the compositions across the solid Si-liquid interface. This research was supported by NSF under Grants DMR-9908855 and DMR-0554792.