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Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem
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Phone: +49 211 6792 722
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Scientific Events

Scientific Events

Month:

18024 1552645836

International Workshop on Advanced and In-situ Microscopies of Functional Nanomaterials and Devices, IAMNano 2019

The workshop aims to provide a forum for researchers who are interested in applying advanced imaging and spectroscopy methods of electron microscopy, including aberration-corrected, in situ, environmental and low-voltage electron microscopy, to topical issues in materials science and engineering, in nanoscience, in soft matter research, in interface and surface science, and in biomaterials research. As these methods are of fundamental importance in virtually all technological fields, contributions are invited that address the broad spectrum of current materials research. Novel methodological developments will be discussed as well as topical areas of research on thin films, bulk materials, surfaces, materials at the nanoscale and at the interface between the physical and life sciences, for understanding structure‐property relationships of materials, as well as for metrology. Selected topics will be introduced by invited keynote speakers during the plenary sessions. A poster session provides room for the presentation and discussion of current research. [more]

MPIE Colloquium

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Exploring the Solar System: From the Nano to Astronomical Scale

Microscopy, by definition, is the science of using a microscope to observe objects that are unseen by the naked eye. However, astronomical objects such as planets, moons and comets or asteroids are easily identifiable in the night sky, yet scientists are increasingly relying on microscopic methods to investigate their composition, structure, and determine their origins. Whether this is via extra-terrestrial exploration with satellites, landers or rovers, or by studying returned astromaterials in the laboratory itself, the use of microscopy within the diverse field of planetary science is quickly becoming the norm. Correlating multiple microscopic and spectroscopic methods within the scanning electron microscope (SEM) when studying meteorites allows us to extend the spectrum from nano or micro-scale imaging at one end, all the way up to the astronomical scale at the other. For example, the Mars Science Laboratory (MSL) rover, Curiosity, landed in Gale Crater; a region that had been heavily investigated using satellite data from previous mission Mars Odyssey. Using similar infrared microscopic methods in the laboratory, we can distinguish the same compositions within Martian meteorites as those directly observed on the Martian surface.Recent studies (e.g. Stephen et al. 2014; King et al. 2018) have combined traditional SEM imaging and analysis (energy-dispersive spectroscopy - EDS, electron-backscatter diffraction – EBSD, wavelength-dispersive spectroscopy – WDS) with micro Fourier transform infrared (μFT-IR) to inform the varied geological histories of meteorite parent bodies, including aqueous alteration on both asteroids and planets. Further studies combine SEM & TEM imaging with other X-ray techniques at varying scales, i.e. X-ray microscopy (XRM) or X-ray tomography (XRT), to help classify new meteorites and examine potential parent bodies throughout the Solar System (MacArthur et al. 2019).Non-destructive, microscopic methods allow for detailed investigation through multiple volumes that would otherwise be inaccessible without damaging the specimens themselves; a crucial consideration when working with limited material from an extra-terrestrial source. Correlating microscopy techniques across instruments, scales and disciplines is perhaps one of the best approaches to studying these astromaterials, and fully unravelling their geological history, as well as their journey to Earth.References:King et al. (2018) Investigating the history of volatiles in the solar system using synchrotron infrared micro-spectroscopy' Infrared Physics and Technology 94, 244-249.MacArthur et al. (2019) Mineralogical constraints on the thermal history of Martian regolith breccia Northwest Africa 8114, Geochimica et Cosmochimica Acta 246, 267-298.Stephen et al. (2014) Mid-IR mapping of Martian meteorites with 8-micron spatial resolution, Meteoritics and Planetary Science, pp A381. [more]

18630 1557316852

Deformation mechanisms in metals under a tribological load

In 1950, Bowden and Tabor pointed out that in metallic tribological contacts the majority of the dissipated energy is spend to change the contacting materials’ microstructures. This – in part – explains why most metals show a highly dynamic subsurface microstructure under the shear load imposed by a sliding contact. In order to understand these processes, the elementary mechanisms accommodating the shear strain and acting in the material need to be revealed and understood. In this presentation, three examples of research avenues following this hypothesis will be given. During the very early stages of sliding, dislocations show an interesting self-organization phenomenon. How these structures interfere with twin boundaries and what might be learned about the dislocation motion under the slider will be the first part of the talk. Second, we will address how the high entropy alloy (HEA) CoCrFeMnNi reacts to a tribological load and whether there is evidence for mechanisms specific to HEAs. Third, we will focus our attention at tribo-chemically activated oxidation process studied for high-purity copper. [more]

Aberration-corrected STEM and ultra-high energy resolution EELS

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Aberration-corrected STEM and ultra-high energy resolution EELS

Electron microscopy has advanced very significantly in the last two decades. Electron-optical correction of aberrations, which we introduced for the scanning transmission electron microscope (STEM) in 1997, has allowed STEMs to reach sub-Å resolution from 2002 on. It has led to new STEM capabilities, such as atomic-resolution elemental mapping, and determining the type of single atoms by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS). More recently, we have focused on Ultra-High Energy Resolution EELS (UHERE). We have developed a monochromator and a spectrometer that use multipolar optics similar to the optics of aberration correctors, plus several stabilization methods, and we have reached <5 meV energy resolution at 30 keV primary energy. This has opened up a new field: vibrational spectroscopy in the electron microscope. When collecting large-angle scattering events, vibrational spectroscopy can lead to sub-nm spatial resolution, and when collecting small-angle scattering angle events, it can produce EEL spectra with the electron beam positioned tens of nm away from the probed area. The second geometry has led to a powerful new technique: aloof vibrational analysis of materials, which avoids significant radiation damage. Even more recently, we have focused on combining the analytical techniques with in-situ sample treatment. Our progress includes cooling the sample to liquid N2 temperature in a side-entry holder capable of reaching better than 1 Å resolution. My talk will review these developments, and illustrate them by application examples. [more]

18319 1555331518

Making quantum transport visible in thermoelectric Bi2Te3 nanoparticles

Bi2Te3, Sb2Te3, and Bi2Se3, well established thermoelectric materials, are also three-dimensional (3D) topological insulators (TI) exhibiting a bulk bandgap and highly conductive, robust, gapless surface states. While the transport properties of 3D TIs are of utmost importance for potential applications, they are difficult to characterize. The reason is that transport in those materials is always dominated by bulk carriers. Still, the signature of the nontrivial electronic band structure on the thermoelectric transport properties can be evidenced in transport experiments using nanostructures with a high surface-to-volume ratio. Using a nanoparticle-based materials’ design, the highly porous macroscopic sample features a carrier density of the surface states in a comparable order of magnitude as the bulk carrier density. Further, the sintered nanoparticles impose energetic barriers for the transport of bulk carriers (hopping transport), while the connected surfaces of the nanoparticles provide a 3D percolation path for surface carriers. Within this work, I will discuss the nanoparticle processing as well as the transport properties of these combined thermoelectric and 3D TI samples. [more]

Nanoindentation based investigations of PLC-type plastic instability

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Nanoindentation based investigations of PLC-type plastic instability

Portevin Le-Chatelier (PLC) effect is a type of plastic instability that results in severe strain localization, reduction in ductility and formation of surface striations during forming operations. Understanding the underlying microscopic mechanism(s) that govern it requires detailed experimental investigations of the relationships between the phenomenon and local microstructural constituents. Most current models of PLC, both phenomenological and theoretical, are based on descriptions of mesoscopic observations and global responses observed in stress-strain curves. More predictive (or physically based) models will require investigations at the microstructural length-scales. In this talk, it will be shown that the gap in understanding of the microscopic origins and macroscopic manifestations of PLC can be bridged by nanoindentation testing. Specifically, it will be shown that by exploiting the high resolution of force and displacement measurements and the site-specific capabilities of the nanoindenter, coupled with complimentary microstructural characterization techniques, we are able to gain new insight into critical aspects of the PLC effect, including its anisotropy, underlying governing mechanisms and associated activation parameters. [more]

The Heusler System (For Thermoelectric Application): How You Can Use the periodic table As A Lego Box To Build The States You Are Interested In

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The Heusler System (For Thermoelectric Application): How You Can Use the periodic table As A Lego Box To Build The States You Are Interested In

The periodic table becomes one hundred years old just this year. The family of Heusler compounds uses nearly all the elements in the Periodic Table to allow for the design of materials with all sorts of properties. These include: hard and soft magnets, shape memory and magnetocaloric metals, thermoelectric semiconductors, topological insulators, and Weyl semimetals. These are just a few examples of more than 1000 known members of this remarkable class of materials that can display such a wide range of extraordinary multifunctional and tunable properties. Many more remain to be discovered! Just like a box of Lego bricks we can put together certain atoms (valence electrons), arranged in a particular symmetry, to achieve a desired electronic energy band structure. A necessary precondition for such a straightforward approach is a single particle picture: this allows for the prediction of many properties in this versatile class of materials, and equally enables “inverse design”. In my talk I will discuss the simple rules that we have learned to date and what the future might portend for further additions to the large and ever-growing Heusler family. [more]

 
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