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Colloquium
Hierarchy of short-circuit diffusion paths on the nanoscale revisited
Wednesday, 04 June 2014, 16:30-18:00
Talk given by Prof. Eugen Rabkin
We studied the solid state dewetting of thin Au, Ni and Fe films, and
Au-Fe bilayers deposited on sapphire substrates. Both Au and Fe films
were nanocrystalline and exhibited strong fiber <111> texture, while
the Ni and Au-Fe films exhibited a strong heteroepitaxy to the
substrate. The single crystalline particles formed at the late stages of
dewetting exhibited stable faceted shapes that were far from those
predicted by equilibrium considerations. We discussed high stability of
faceted particles in terms of very slow mass transport along the
singular atomically flat facets. In the case of heteroepitaxial Ni films
and Au-Fe bilayers, the formation of highly faceted pinholes to the
substrate is accompanied by the nucleation and growth of twin
boundaries parallel to the substrate. These boundaries allow
nucleating of defects at the side facets of the pinhole, thus enabling its
growth.
We argue that the slow pace of diffusion on atomically flat facets
of nanoparticles and textured thin films brings to the forefront other
types of short-circuit diffusion, such as grain boundary diffusion and
metal self-diffusion along the interphase boundaries (i.e. along the
film-substrate interface). We propose a general framework for treating
the size and shape evolution in nanocrystalline and nano-particulate
solids controlled by diffusion along the interphase boundaries between
two immiscible, non-reactive phases. Like in the case of surface
diffusion, the atomic diffusion flux along the interphase boundary is
driven by the gradient of chemical potential of the atoms at the
interface. Yet while in the case of surface diffusion this chemical
potential is a local function of surface curvature and surface energy, in
the case of interphase boundary the chemical potentials of the
components depend on the overall geometry of the system and on
boundary conditions at the triple lines. We suggest a variational
method of calculating the chemical potentials at the interphase
boundary. This method relies on calculating the variations of the total
energy of the system caused by infinitesimal relative translations and
rotations of the two solid phases abutting the interface.
Our theoretical models are illustrated by the experimental data on
sintering of model Cu-W agglomerates, on phase transformations in
the nanoparticles of Au-Fe alloys, and on thermal grooving in thin Ni
films with “mazed bicrystal” microstructure.
This event is part of the eventgroup INT Talks
Homepage
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Speaker
Prof. Eugen Rabkin
Technion - Israel Institute of Technology
Materials Engineering
Prof. Eugen Rabkin
Technion - Israel Institute of Technology
Materials Engineering
Organizer
Prof. Dr.-Ing. Horst Hahn
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Mail: horst hahn ∂ kit edu
Prof. Dr.-Ing. Horst Hahn
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Mail: horst hahn ∂ kit edu
Targetgroup
Interested / Everyone
Interested / Everyone