Informal DQMP Seminar

Carte non disponible

Day / Time
Date(s) - 20/11/2015
11 h 00 min - 12 h 30 min

Category


Salle MaNEP, Ecole de physique

20 November 2015 (Friday), 11h00

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Dr. Ducan Alexander

Interdisciplinary Centre for Electron Microscopy (CIME)

Ecole Polytechnique Fédérale de Lausanne (EPFL)

Illuminating materials physics and chemistry with aberration-corrected and monochromated transmission electron microscopy

Modern transmission electron microscopy (TEM) provides an incredibly versatile platform for interrogating the physical and chemical nature of matter, down to the atomic scale. In particular, the advent of aberration correctors, combined with faster, more sensitive spectrometers, has shifted paradigms for what can be achieved. In this talk I will present results taken with the double aberration-corrected, monochromated FEI Titan Themis recently installed at CIME, EPFL – currently the most powerful electron microscope in Switzerland. I will show how different techniques are used to gain pertinent information for a variety of questions in materials physics and chemistry. Firstly, as device structures shrink or are reduced in dimensionality, it is critical to understand the nature of their defects at the atomic level. To do so, we apply low-kV scanning TEM (STEM) with a sub-Å probe to characterize vacancies and topological defects in 2D monolayers of semiconducting MoS2 grown by CVD. As researchers functionalize inorganic materials with active organic molecules for biomedical applications, there is a challenge to understand the “soft/hard” interfaces so created. Here, I use low-kV high resolution TEM with a monochromated, highly coherent incident beam to image the morphology of ligands attached to iron oxide nanoparticles, towards the aim of linking observations to theoretical calculations of ligand bonding. For other technologies, understanding the chemistry across hard/hard interfaces is equally as important. The latest generation of energy-dispersive X-ray detectors, combined with aberration-corrected STEM, provides a powerful tool to do so, as demonstrated with the identification of chemical diffusion across atomic columns in the strain field of misfit dislocations at an epitaxial interface in perovskite ferroelectrics. Finally, for optimising devices based on plasmonic and photonic structures, it is important to map their optical excitations with a nano-scale spatial resolution. I do so using high-energy resolution electron energy-loss spectroscopy with a monochromated incident STEM probe. This technique rapidly reveals both the spatial distribution and peak energies of plasmon excitations between Au nano-rod assemblies. Comparison to simulations proves that we can precisely measure both bright and dark modes. Given this confirmation, in a next step this strategy will be applied to evaluate more complicated plasmonic structures.

 

Réalisation : Sur Mesure concept