Article
Multidisciplinary Sciences
D-S Park, M. Hadad, L. M. Riemer, R. Ignatans, D. Spirito, V Esposito, V Tileli, N. Gauquelin, D. Chezganov, D. Jannis, J. Verbeeck, S. Gorfman, N. Pryds, P. Muralt, D. Damjanovic
Summary: This study breaks the crystallographic symmetry and induces large and sustainable piezoelectric effects in centrosymmetric materials. The experiment shows the generation of extraordinarily large piezoelectric responses in cubic fluorite gadolinium-doped CeO2-x films, which are two orders of magnitude larger than the responses observed in the presently best-known lead-based piezoelectric relaxor-ferroelectric oxide. This finding provides opportunities to design environmentally friendly piezoelectric materials.
Article
Microscopy
D. Jannis, C. Hofer, C. Gao, X. Xie, A. Beche, T. J. Pennycook, J. Verbeeck
Summary: Four dimensional scanning transmission electron microscopy (4D STEM) records electron scattering in materials in great detail, but the requirement for 2D image recording at each probe position has long limited its speed. Recent advances in camera technology, especially direct electron detectors, have reduced this bottleneck.
Article
Materials Science, Multidisciplinary
N. Lebedev, Y. Huang, A. Rana, D. Jannis, N. Gauquelin, J. Verbeeck, J. Aarts
Summary: In this paper, we studied the properties of LaAlO3/Eu1-xLaxTiO3/SrTiO3 structures and found that they have similar characteristics to previously studied LaAlO3/EuTiO3/SrTiO3 and other oxide interfaces. These include the formation of a two-dimensional electron liquid for the Eu1-xLaxTiO3 layer, a metal-insulator transition driven by the thickness of the Eu1-xLaxTiO3 layer, the presence of an anomalous Hall effect when driving the systems above the Lifshitz point with a back-gate voltage, and a minimum in the temperature dependence of the sheet resistance below the Lifshitz point in the one-band regime. However, the observed minimum in sheet resistance is not attributed to the Kondo effect, but rather to the properties of the SrTiO3 crystal and the effects of charge trapping when using back gates.
PHYSICAL REVIEW MATERIALS
(2022)
Article
Microscopy
D. Jannis, A. Velazco, A. Beche, J. Verbeeck
Summary: The study aimed to construct an empirical model to mimic the impact of alternative scan patterns on beam damage in a specific zeolite sample. By adjusting dwell time and probe position distance, the model qualitatively described various aspects of experimental data and provided guidance for optimizing beam damage without reducing electron dose.
Article
Multidisciplinary Sciences
Jaianth Vijayakumar, Tatiana M. Savchenko, David M. Bracher, Gunnar Lumbeeck, Armand Beche, Jo Verbeeck, Stefan Vajda, Frithjof Nolting, C. A. F. Vaz, Armin Kleibert
Summary: This paper provides a detailed understanding of the oxidation process of cobalt nanoparticles and evaluates the development of models for metal oxidation and magnetic phenomena at the nanoscale. Understanding the chemical reactivity and magnetism of 3d transition metal nanoparticles is essential for applications in spintronics and catalysis.
NATURE COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Christoph Hofer, Kimmo Mustonen, Viera Skakalova, Timothy J. Pennycook
Summary: This article presents a new method for precise local 3D atomic structure analysis of 2D materials. By combining few tilt tomography with highly dose efficient ptychography, it becomes possible to analyze fragile 2D materials, particularly for the analysis of local defects.
Article
Nanoscience & Nanotechnology
G. Verdierre, N. Gauquelin, D. Jannis, Y. A. Birkholzer, S. Mallik, J. Verbeeck, M. Bibes, G. Koster
Summary: This study reports the growth of SrBiO3 films on SrTiO3 and NdScO3 substrates. It was found through high-resolution transmission electron microscopy that SrBiO3 exhibits slight tensile strain on SrTiO3, contrary to the expected compressive strain due to lattice mismatch, which is caused by structural domain matching. This work provides a framework for the synthesis of high-quality perovskite bismuthates films and the understanding of their interface interactions with homostructural substrates.
Article
Microscopy
C. Gao, C. Hofer, T. J. Pennycook
Summary: Ptychography provides high dose efficiency images that can reveal light elements next to heavy atoms. However, contrast reversals can occur when the projected potential becomes strong. Recent research has shown that these reversals can be counteracted by adapting the focus. This study explains why the best contrast is often found with the probe focused to the middle of the sample and highlights the importance of convergence angle in thin samples to remove contrast reversals.
Article
Microscopy
Christoph Hofer, Timothy J. Pennycook
Summary: Electron ptychography is an effective and sensitive technique for phase imaging. However, quantifying the ptychographic phases of atomic sites remains a challenge. This article presents a new method that overcomes this challenge, especially for 2D materials, and is robust to experimental parameters such as noise and sample tilt.
