Compositional study of defects in microcrystalline silicon solar cells using spectral decomposition in the scanning transmission electron microscope

The chemical compositions of defective regions in microcrystalline thin film Si solar cells are studied using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope. Nanometer-resolved chemical analysis reveals the presence of ZnO in micrometer-long defective regions. Due to the recent application of unmixing algorithm to EELS, the chemical compositions of the defective regions are determined objectively, without introducing artefacts from the fitting procedures. It is shown that the defective regions in the Si layer are filled by ZnO, which diffuses along voids that propagate from the bottom up to the top ZnO contacts. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4800569]

Multi-modal and multi-scale non-local means method to analyze spectroscopic datasets

Martial Duchamp, Vasiliki Tileli

A multi-modal and multi-scale non-local means (M3S-NLM) method is proposed to extract atomically resolved spectroscopic maps from low signal-to-noise (SNR) datasets recorded with a transmission electron microscope. This method improves upon previously tested denoising techniques as it takes into account the correlation between the dark-field signal recorded simultaneously with the spectroscopic dataset without compromising on the spatial resolution. The M3S-NLM method was applied to electron energy dispersive X-ray and electron-energy-loss spectroscopy (EELS) datasets. We illustrate the retrieval of the atomic scale diffusion process in an Al1-xInxN alloy grown on GaN and the surface oxidation state of perovskite nanocatalysts. The improved SNR of the EELS dataset also allows the retrieval of atomically resolved oxidation maps considering the fine structure absorption edge of LaMnO3 nanoparticles.

ELSEVIER2019

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

Preparation of homogeneous titania coatings on the surface of MWNTs

Duncan Alexander, László Forró, Klara Hernadi, Jin Won Seo

The aim of this work was to develop a controllable route to produce a stable and inorganic layer on the surface of multi-wall carbon nanotubes. Precursor compounds such as TiBr4, TiCl4, Ti(OiPr)(4), and Ti(OEt)(4) were used to cover the surface of carbon nanotubes (CNTs) under either solvent free or solution conditions. Various titania precursors were compared in the formation of homogeneous layers on the surface of CNTs. As-prepared titania coverages were characterized by transmission electron microscopy (TEM), high resolution TEM, scanning electron microscopy, electron energy loss spectroscopy, and Xray diffraction techniques. Results revealed that homogeneous coverage can be achieved in a controllable way. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2010

Angular Resolved low loss EELS for Materials Characterization

Simon Schneider

EPFL2013