Showing 1–6 of 6 results for author: Hsiao, H

Chemical Short-Range Ordering in a CrCoNi Medium-Entropy Alloy

Authors: H. W. Hsiao, R. Feng, H. Ni, K. An, J. D. Poplawsky, P. K. Liaw, J. M. Zuo

Abstract: The exceptional mechanical strengths of medium and high-entropy alloys have been attributed to hardening in random solid solutions. Here, we evidence non-random chemical mixings in CrCoNi alloys, resulting from short range ordering. A novel data-mining approach of electron nanodiffraction patterns enabled the study, which is assisted by neutron scattering, atom probe tomography, and diffraction si… ▽ More The exceptional mechanical strengths of medium and high-entropy alloys have been attributed to hardening in random solid solutions. Here, we evidence non-random chemical mixings in CrCoNi alloys, resulting from short range ordering. A novel data-mining approach of electron nanodiffraction patterns enabled the study, which is assisted by neutron scattering, atom probe tomography, and diffraction simulation using first principles theory models. Results reveal two critical types of short range orders in nanoclusters that minimize the Cr and Cr nearest neighbors (L11) or segregate Cr on alternating close-packed planes (L12). The makeup of ordering-strengthened nanoclusters can be tuned by heat treatments to affect deformation mechanisms. These findings uncover a mixture of bonding preferences and their control at the nanoscopic scale in CrCoNi and provide general opportunities for an atomistic-structure study in concentrated alloys for the design of strong and ductile materials. △ Less

Submitted 4 June, 2022; originally announced June 2022.

Data-Driven Electron Microscopy: Electron Diffraction Imaging of Materials Structural Properties

Authors: Jian-Min Zuo, Renliang Yuan, Yu-Tsun Shao, Haw-Wen Hsiao, Saran Pidaparthy, Yang Hu, Qun Yang, Jiong Zhang

Abstract: Transmission electron diffraction is a powerful and versatile structural probe for the characterization of a broad range of materials, from nanocrystalline thin films to single crystals. With recent developments in fast electron detectors and efficient computer algorithms, it now becomes possible to collect unprecedently large datasets of diffraction patterns (DPs) and process DPs to extract cryst… ▽ More Transmission electron diffraction is a powerful and versatile structural probe for the characterization of a broad range of materials, from nanocrystalline thin films to single crystals. With recent developments in fast electron detectors and efficient computer algorithms, it now becomes possible to collect unprecedently large datasets of diffraction patterns (DPs) and process DPs to extract crystallographic information to form images or tomograms based on crystal structural properties, giving rise to data-driven electron microscopy. Critical to this kind of imaging is the type of crystallographic information being collected, which can be achieved with a judicious choice of electron diffraction techniques, and the efficiency and accuracy of DP processing, which requires the development of new algorithms. Here, we review recent progress made in data collection, new algorithms, and automated electron DP analysis. These progresses will be highlighted using application examples in materials research. Future opportunities based on smart sampling and machine learning are also discussed. △ Less

Submitted 5 October, 2021; originally announced October 2021.

Comments: 28 pages, 14 Figures and 135 references, accepted for a special issue of Microscopy (Oxford)

Cepstral Scanning Transmission Electron Microscopy Imaging of Severe Lattice Distortions

Authors: Yu-Tsun Shao, Renliang Yuan, Haw-Wen Hsiao, Qun Yang, Yang Hu, Jian-Min Zuo

Abstract: The development of four-dimensional (4D) scanning transmission electron microscopy (STEM) using fast detectors has opened-up new avenues for addressing some of long-standing challenges in electron imaging. One of these challenges is how to image severely distorted crystal lattices, such as at a dislocation core. Here we introduce a new 4D-STEM technique, called Cepstral STEM, for imaging disordere… ▽ More The development of four-dimensional (4D) scanning transmission electron microscopy (STEM) using fast detectors has opened-up new avenues for addressing some of long-standing challenges in electron imaging. One of these challenges is how to image severely distorted crystal lattices, such as at a dislocation core. Here we introduce a new 4D-STEM technique, called Cepstral STEM, for imaging disordered crystals using electron diffuse scattering. Local fluctuations of diffuse scattering are captured by scanning electron nanodiffraction (SEND) using a coherent probe. The harmonic signals in electron diffuse scattering are detected through Cepstral analysis and used for imaging. By integrating Cepstral analysis with 4D-STEM, we demonstrate that information about the distortive part of electron scattering potential can be separated and imaged at nm spatial resolution. We apply our technique to the analysis of a dislocation core in SiGe and lattice distortions in high entropy alloy. △ Less

Submitted 16 January, 2021; originally announced January 2021.

Comments: 21 pages, 8 figures

Discovery of two-dimensional anisotropic superconductivity at KTaO$_3$ (111) interfaces

Authors: Changjiang Liu, Xi Yan, Dafei Jin, Yang Ma, Haw-Wen Hsiao, Yulin Lin, Terence M. Bretz-Sullivan, Xianjing Zhou, John Pearson, Brandon Fisher, J. Samuel Jiang, Wei Han, Jian-Min Zuo, Jianguo Wen, Dillon D. Fong, Jirong Sun, Hua Zhou, Anand Bhattacharya

Abstract: The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. Here we observe superconductivity in electron gases formed at interfaces between (111) oriented KTaO$_3$ and insulating overlayers of either EuO or LaAlO$_3$. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the L… ▽ More The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. Here we observe superconductivity in electron gases formed at interfaces between (111) oriented KTaO$_3$ and insulating overlayers of either EuO or LaAlO$_3$. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the LaAlO$_3$/SrTiO$_3$ system. Strikingly, similar electron gases at (001) KTaO$_3$ interfaces remain normal down to 25 mK. The critical field and current-voltage measurements indicate that the superconductivity is two dimensional. Higher mobility EuO/KTaO$_3$ (111) samples show a large in-plane anisotropy in transport properties at low temperatures prior to onset of superconductivity, suggesting the emergence of a stripe like phase where the superconductivity is nearly homogeneous in one direction, but strongly modulated in the other. △ Less

Submitted 15 April, 2020; originally announced April 2020.

Journal ref: Science 371, Issue 6530, pp. 716-721 (2021)

Doped NiO: the Mottness of a charge transfer insulator

Authors: Friederike Wrobel, Hyowon Park, Changhee Sohn, Haw-Wen Hsia, Jian-Min Zuo, Hyeondeok Shin, Ho Nyung Lee, P. Ganesh, Anouar Benali, Paul R. C. Kent, Olle Heinonen, Anand Bhattacharya

Abstract: The evolution of the electronic structures of strongly correlated insulators with doping has long been a central fundamental question in condensed matter physics; it is also of great practical relevance for applications. We have studied the evolution of NiO under hole {\em and} electron doping using high-quality thin film and a wide range of experimental and theoretical methods. The evolution is i… ▽ More The evolution of the electronic structures of strongly correlated insulators with doping has long been a central fundamental question in condensed matter physics; it is also of great practical relevance for applications. We have studied the evolution of NiO under hole {\em and} electron doping using high-quality thin film and a wide range of experimental and theoretical methods. The evolution is in both cases very smooth with dopant concentration. The band gap is asymmetric under electron and hole doping, consistent with a charge-transfer insulator picture, and is reduced faster under hole than electron doping. For both electron and hole doping, occupied states are introduced at the top of the valence band. The formation of deep donor levels under electron doping and the inability to pin otherwise empty states near the conduction band edge is indicative that local electron addition and removal energies are dominated by a Mott-like Hubbard $U$-interaction even though the global bandgap is predominantly a charge-transfer type gap. △ Less

Submitted 11 May, 2020; v1 submitted 30 January, 2020; originally announced January 2020.

Comments: Revised version

Journal ref: Phys. Rev. B 101, 195128 (2020)

Molecular beam epitaxy of the magnetic kagome metal FeSn on LaAlO3 (111)

Authors: Deshun Hong, Changjiang Liu, Haw-Wen Hsiao, Dafei Jin, John E. Pearson, Jian-Min Zuo, Anand Bhattacharya

Abstract: Materials with a layered Kagome lattice are expected to give rise to novel physics arising from band structures with topological properties, spin liquid behavior and the formation of skyrmions. Until now, most work on Kagome materials has been performed on bulk samples due to difficulties in thin film synthesis. Here, by using molecular beam epitaxy, layered Kagome-structured FeSn films are synthe… ▽ More Materials with a layered Kagome lattice are expected to give rise to novel physics arising from band structures with topological properties, spin liquid behavior and the formation of skyrmions. Until now, most work on Kagome materials has been performed on bulk samples due to difficulties in thin film synthesis. Here, by using molecular beam epitaxy, layered Kagome-structured FeSn films are synthesized on (111) oriented LaAlO3 substrate. Both in-situ and ex-situ characterizations indicate these films are highly crystalline and c-axis oriented, with atomically smooth surfaces. However, the films grow as disconnected islands, with lateral dimensions on the micron scale. By patterning Pt electrodes using a focused electron beam, longitudinal and transverse resistance of single islands have been measured in magnetic fields. Our work opens a pathway for exploring mesoscale transport properties in thin films of Kagome materials and related devices. △ Less

Submitted 15 November, 2020; v1 submitted 6 January, 2020; originally announced January 2020.

Journal ref: AIP Advances 10, 105017 (2020)