Talk given by Dr. Di Wang Nowadays new nanomaterials often involve complex structures of interfaces and surfaces, doped and alloyed elements in nanometer sized domains, which are crucial for the performance of the material. Therefore it is an absolute prerequisite to characterize and understand these structures at the nanometer and even at the atomic scale in order to precisely design new nanomaterials. Modern TEM techniques are one of the few approaches that offer versatile capabilities to comprehensively characterize material structures up to the atomic scale and to directly correlate the structure with the physical and chemical properties of the nanomaterials. With the development of aberration correction, sub-Ångstrom resolution has been achieved, enabling direct observation of atomic configurations. EDX and EELS spectra from very local areas offer methods to study e.g. elemental distributions and interfacial phenomena with sub-nanometer resolution. In addition, electron tomography overcomes the limitations of 2D projections and reconstructs the 3D structure from a tilt series of images to resolve nanometer-sized objects or voids distribution. Within POF and KNMF projects currently being carried out in INT, TEM has been applied to various material systems. In this presentation the study of interfacial structures in nanoglasses and nanocatalysts will be highlighted particularly. In both systems, interfacial structures become highly important with decreasing size of nanoparticles. These structures are expected to lead to special physical or chemical properties that conventional materials do not have. With the high resolution imaging and analytic techniques available in the Titan 80- 300 electron microscope, structures of the FeSc primary particles synthesized by inert gas condensation (IGC) and of the pellets after HPT processing have been identified to illustrate the effect of HPT on the inter-particle structure. In addition, sputtered Ti-Ni-Cu nanoglasses are shown to form aggregated primary particles with Ti oxide between particles and a gap between aggregates. In the future efforts will be concentrated on preparing thin TEM nanoglass specimens, either from IGC or from sputtering, and using high resolution imaging and spectroscopic methods to clarify the interface structures, whether they are due to solute segregation or to changed atomic configurations close to the triple junctions between particles or whether there is a new phase formed at the interface. Combining electron tomography and atom probe will offer information about the composition and density variations at the interface. The results are expected to provide a direct evidence to explain the observed special properties, e.g., the ferromagnetic behavior in consolidated FeSc nanoglasses. Recent studies in some selected liquid phase and gas phase catalytic reactions have shown clearly that not only the size but also the shape of supported metal nanoparticles plays an essential role in activity and selectivity of a catalytic reaction. It will be shown in this presentation that the shape of Au particles is highly dependent on the surface structure of the carbon support. Furthermore, by choosing impregnation or colloidal synthetic methods, particles were deposited both inside and outside or exclusively outside tubular CNFs, as revealed by electron tomography. The shape and the anchoring site of the Au particles were directly correlated to the selectivity of the catalysts in alcohol oxidations. In order to further investigate the size, support and synergistic bimetallic effects, model catalyst systems such as size selected clusters, metal catalysts supported on mesoporous supports and bimetallic nanocatalysts will be studied by TEM imaging and EDX/EELS spectroscopy to unravel the particle morphology, elemental distribution as well as to quantify the percentage of different types of particle.

This event is part of the eventgroup INT Talks

Homepage
https://www.int.kit.edu/events.php

Speaker
Dr. Di Wang

Karlsruhe Institute of Technology (KIT)
Institute of Nanotechnology (INT)

Organizer
Prof. Dr.-Ing. Horst Hahn
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Mail: horst hahn ∂does-not-exist.kit edu

Targetgroup
Interested / Everyone