Effects of Kr and Xe ion irradiation on the structure of Y2O3 nanoprecipitates in YBCO thin film conductors

The response of Y2O3 nanoprecipitates in a 1-mu m YBa2Cu3O7-x layer from a superconducting wire Ag/YBCO/buffer metal oxides/Hastelloy to 107 MeV Kr and 167 MeV Xe ion irradiation was investigated using a combination of transmission electron microscopy, diffraction and X-ray energy-dispersive spectrometry. The direct observation of the radiation-induced tracks in Y2O3 nanocrystals is reported for the first time to the authors' best knowledge. Structureless damaged regions of 5-9 nm (average 8 nm) in diameter were observed in Y2O3 nanocrystals when the electronic stopping power S-e was about or higher than 4.7 keV/nm. This value of S-e is the upper estimate of the minimum electronic stopping power to create damage in yttria nanocrystals. The electron diffraction patterns, high-resolution transmission electron microscopy, high-resolution scanning transmission electron microscopy, Fourier transform patterns from areas extending a few nanometres around the tracks show that yttria and YBCO keep their respective cubic and orthorhombic pristine structures.

Microstructure, properties and biocompatibility of the nitrided Ti-6Al-4V alloy for medical application

Philippe Buffat

Investigation of the microstructure, properties and biocompatibility of the Ti-6Al-4V alloy nitrided under glow discharge was performed. The microstructural analyses were carried out using light microscopy, X-ray diffraction, analytical scanning and transmission electron microscopy. Phase identifications and chemical composition of the layer and bulk material (substrate) were determined by electron diffraction and energy dispersive X-ray spectrometry. Atomic force microscopy was applied for layer surface topography measurements. Microhardness and Young's modulus measurements as well as frictional wear resistance and corrosion resistance tests were performed. The investigation revealed a clear correlation between the micro/nano structure and surface topography of the layer with its micromechanical, tribological and corrosion properties. In-vitro examinations of biofilm and cell behaviour show that the nitrided Ti-6Al-4V alloy exhibits good biocompatibility.

2006

Angular Resolved low loss EELS for Materials Characterization

Simon Schneider

Electron Energy Loss Spectrometry (EELS) in Transmission Electron Microscopy (TEM) is a powerful tool for the investigation of the electronic structure of materials. In the low loss regime, one can access the optical properties which are governed by the dielectric function ε(ω), which may be retrieved thanks to the so-called "loss function". The energy range covered by EELS goes from the infrared (less than 1 eV) to the hard X-rays (about 3 keV), each region having its own interest. The low loss region (0–100 eV) serves to investigate the valence electron structure and the inter-band transition behavior. Using angular resolved EELS gives further information about the dispersion behavior of the investigated material. This work is a part of a large project aiming a closer agreement between theory and experiment in angular resolved EELS by improving the state of the art in both fields. The purpose of this work is to set up a reliable experimental technique to retrieve the momentum transfer resolved single scattering distribution at very low energy with good accuracy and resolutions. One of the main challenges was to use the newly installed JEOL 2200 FS transmission electron microscope that is equipped with an in-column Ω filter for retrieval of the loss function in diffraction energy filtered TEM. Issues such as the angular resolution, contamination, image-coupling in diffraction mode and plural scattering have been solved. Several optical alignments and operational modes of the JEOL 2200 FS have been tested, and finally nano-beam diffraction was found to be the optimal running mode. This work provides for the first time a full 3D energy loss data cube in diffraction mode with energy and angular resolutions of 1 eV and 0.5 nm−1 respectively. After processing, the energy and angular relevant data span an energy loss range from 2.75 eV to 40.25 eV and the angular momentum transfer up to 12.5 nm−1. Although theoretically, without CCD camera binning and the maximum available camera length of the JEOL (250 cm), a momentum transfer resolution of 0.04 nm−1 would have been possible, the effective angular resolution was limited by the smallest obtainable beam convergence as well as by the remaining aberrations of the microscope. The presented technique can be reproduced on any transmission electron microscope equipped with an in-column energy filter. Furthermore, it is demonstrated that the proposed method provides working ranges in energy, spatial and angular resolutions limited only by the perfor- mance of the microscope. Previous techniques did not provide experimental results showing an energy resolution independent of the spatial and angular resolutions.

EPFL2013

Identification of nano-phases: relative merit of local analysis techniques (HRTEM, nanodiffraction, EDS/EELS)

Philippe Buffat

Information for phase identification may be gathered in the electron transmission microscope with spatial resolution down to the nanometre scale. Energy dispersive X-ray and electron energy loss spectrometries are based on inelastic electron/sample interaction. They have the advantage to give a direct knowledge of the chemical nature of the atoms under the electron probe, sometimes also with valence and bonding, but concentrations are mean values over all atoms in the excited volume that may be insufficient when composition is not uniform. Moreover, X-ray absorption, electron scattering and channeling may lead to errors hard to notice and correct. Elastic interaction is observed on diffraction patterns for crystalline phases with the advantage that superimposed patterns in the case of mixtures are easily most often differentiated . It leads to phase identification via crystallographic databases. When the scale of investigation goes down to a few nanometres or tens of nanometres, indexing diffractograms of high-resolution transmission electron microscopy images is attractive, but it is often forgotten that such diffractograms are not actual diffraction patterns of the crystal itself and that lattice spacings may even be shifted by several per-cents in spheroidal nanoparticles.

2004

Angular Resolved low loss EELS for Materials Characterization

Simon Schneider

EPFL2013