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204 results on '"Du, Hongchu"'

1. Structure of $180^\circ$ ferroelectric domain walls in $\mathrm{HfO_2}$ and $\mathrm{ZrO_2}$

Author

Du, Hongchu

Subjects
Condensed Matter - Materials Science
Abstract

We report two series of structures representing two types of $180^\circ$ ferroelectric domain walls in $\mathrm{HfO_2}$ and $\mathrm{ZrO_2}$. We model the domain structures with different width by density functional theory calculations. The results reveal the dependency of domain wall energy and polarization on domain width. We show how the directions of polarization of ferroelectric domains can be determined from experimentally observed Hf atoms, despite the fact that the knowledge about the positions of O atoms is missing. The two series of structures thus provide more thorough interpretation and hence deeper understanding of experimental observations by transmission electron microscopy.

Published
2022

2. Atomic-Scale Insights into Nickel Exsolution on LaNiO3 Catalysts via In Situ Electron Microscopy

Author

Cao, Pengfei, Tang, Pengyi, Bekheet, Maged F, Du, Hongchu, Yang, Luyan, Haug, Leander, Gili, Albert, Bischoff, Benjamin, Gurlo, Aleksander, Kunz, Martin, Dunin-Borkowski, Rafal E, Penner, Simon, and Heggen, Marc

Subjects
Macromolecular and Materials Chemistry, Chemical Sciences, Physical Chemistry, Engineering, Materials Engineering, Technology, Chemical sciences
Abstract

Using a combination of in situ bulk and surface characterization techniques, we provide atomic-scale insight into the complex surface and bulk dynamics of a LaNiO3 perovskite material during heating in vacuo. Driven by the outstanding activity LaNiO3 in the methane dry reforming reaction (DRM), attributable to the decomposition of LaNiO3 during DRM operation into a Ni//La2O3 composite, we reveal the Ni exsolution dynamics both on a local and global scale by in situ electron microscopy, in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy. To reduce the complexity and disentangle thermal from self-activation and reaction-induced effects, we embarked on a heating experiment in vacuo under comparable experimental conditions in all methods. Associated with the Ni exsolution, the remaining perovskite grains suffer a drastic shrinkage of the grain volume and compression of the structure. Ni particles mainly evolve at grain boundaries and stacking faults. Sophisticated structure analysis of the elemental composition by electron-energy loss mapping allows us to disentangle the distribution of the different structures resulting from LaNiO3 decomposition on a local scale. Important for explaining the DRM activity, our results indicate that most of the Ni moieties are oxidized and that the formation of NiO occurs preferentially at grain edges, resulting from the reaction of the exsolved Ni particles with oxygen released from the perovskite lattice during decomposition via a spillover process from the perovskite to the Ni particles. Correlating electron microscopy and X-ray diffraction data allows us to establish a sequential two-step process in the decomposition of LaNiO3 via a Ruddlesden-Popper La2NiO4 intermediate structure. Exemplified for the archetypical LaNiO3 perovskite material, our results underscore the importance of focusing on both surface and bulk characterization for a thorough understanding of the catalyst dynamics and set the stage for a generalized concept in the understanding of state-of-the art catalyst materials on an atomic level.

Published
2022

3. Highly Complex Magnetic Structures Resulting From Hierarchical Phase Separation in AlCo(Cr)FeNi High Entropy Alloys

Author

Lan, Qianqian, Kovács, András, Caron, Jan, Du, Hongchu, Song, Dongsheng, Dasari, Sriswaroop, Gwalani, Bharat, Chaudhary, Varun, Ramanujan, Raju V., Banerjee, Rajarshi, and Dunin-Borkowski, Rafal E.

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Magnetic high entropy alloys (HEAs) are a new category of high-performance magnetic materials, with multi-component concentrated compositions and complex multi-phase structures. Although there have been numerous reports of their interesting magnetic properties, there is very limited understanding about the interplay between their hierarchical multi-phase structures and their local magnetic structures. By employing high spatial resolution correlative magnetic, structural and chemical studies, we reveal the influence of a hierarchically decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of magnetic vortex states within individual A2 (disordered BCC) precipitates, which are distributed in an ordered B2 matrix that is weakly ferromagnetic. Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are also observed. These results provide important insight into the origin of coercivity in this HEA, which can be attributed to a complex magnetization process that includes the successive reversal of magnetic vortices.

Published
2021

4. Multiple polarization orders in individual twinned colloidal nanocrystals of centrosymmetric HfO2

Author

Du, Hongchu, Groh, Christoph, Jia, Chun-Lin, Ohlerth, Thorsten, Urban, Knut W., Dunin-Borkowski, Rafal E., Simon, Ulrich, and Mayer, Joachim

Subjects
Condensed Matter - Materials Science
Abstract

Spontaneous polarization is essential for ferroelectric functionality in non-centrosymmetric crystals. High-integration-density ferroelectric devices require the stabilization of ferroelectric polarization in small volumes. Here, atomic-resolution transmission electron microscopy imaging reveals that twinning-induced symmetry breaking in colloidal nanocrystals of centrosymmetric HfO2 leads to the formation of multiple polarization orders, which are associated with sub-nanometer ferroelectric and antiferroelectric phases. The minimum size limit of the ferroelectric phase is found to be ~4 nm3. Density functional theory calculations indicate that transformations between the ferroelectric and antiferroelectric phases can be modulated by lattice strain and are energetically possible in either direction. The results of this work provide a route towards applications of HfO2 nanocrystals in information storage at densities that are more than an order of magnitude higher than the scaling limit defined by the nanocrystal size.

Published
2020
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5. Changing the Phosphorus Allotrope from a Square Columnar Structure to a Planar Zigzag Nanoribbon by Increasing the Diameter of Carbon Nanotube Nanoreactors

Author

Zhang, Jinying, Fu, Chengcheng, Song, Shixin, Du, Hongchu, Zhao, Dan, Huang, Hongyang, Zhang, Lihui, Guan, Jie, Zhang, Yifan, Zhao, Xinluo, Ma, Chuansheng, Jia, Chun-Lin, and Tomanek, David

Subjects
Condensed Matter - Materials Science
Abstract

Elemental phosphorus nanostructures are notorious for a large number of allotropes, which limits their usefulness as semiconductors. To limit this structural diversity, we synthesize selectively quasi-1D phosphorus nanostructures inside carbon nanotubes (CNTs) that act both as stable templates and nanoreactors. Whereas zigzag phosphorus nanoribbons form preferably in CNTs with an inner diameter exceeding 1.4 nm, a previously unknown square columnar structure of phosphorus is observed to form inside narrower nanotubes. Our findings are supported by electron microscopy and Raman spectroscopy observations as well as ab initio density functional theory calculations. Our computational results suggest that square columnar structures form preferably in CNTs with inner diameter around 1.0 nm, whereas black phosphorus nanoribbons form preferably inside CNTs with 4.1 nm inner diameter, with zigzag nanoribbons energetically favored over armchair nanoribbons. Our theoretical predictions agree with the experimental findings.

Published
2020
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8. Direct growth of single-metal-atom chains

Author

Guo, Shasha, Fu, Jiecai, Zhang, Peikun, Zhu, Chao, Yao, Heming, Xu, Manzhang, An, Boxing, Wang, Xingli, Tang, Bijun, Deng, Ya, Salim, Teddy, Du, Hongchu, Dunin-Borkowski, Rafal E., Xu, Mingquan, Zhou, Wu, Tay, Beng Kang, Zhu, Chao, He, Yanchao, Hofmann, Mario, Hsieh, Ya-Ping, Guo, Wanlin, Ng, Michael, Jia, Chunlin, Zhang, Zhuhua, He, Yongmin, and Liu, Zheng

Published
2022
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10. List of contributors

Author

Birkhölzer, Yorick, primary, Bowen, M., additional, Cao, Yanwei, additional, Cheng, Guanglei, additional, Choi, Woo Seok, additional, Combs, Nicholas G., additional, Dawber, M., additional, Dittmann, Regina, additional, Do, Minh T., additional, Du, Hongchu, additional, Esposito, Vincenzo, additional, Fong, D.D., additional, Guo, Hangwen, additional, Houwman, Evert P., additional, Huijben, Mark, additional, Jia, Chun-Lin, additional, Kajdos, Adam P., additional, Kornblum, Lior, additional, Koster, Gertjan, additional, Krockenberger, Yoshiharu, additional, Lee, Ho Nyung, additional, Leon, Carlos, additional, Liao, Zhaoliang, additional, Naito, Michio, additional, Okkerman, Luuk, additional, Pryds, Nini, additional, Rijnders, Guus, additional, Sambri, Alessia, additional, Santamaria, Jacobo, additional, Santucci, Simone, additional, Seo, Ambrose, additional, Smink, Sander, additional, Sohn, Changhee, additional, Spreitzer, Matjaž, additional, Stemmer, Susanne, additional, ten Elshof, Johan E., additional, Vailionis, Arturas, additional, Wang, LingFei, additional, Yamamoto, Hideki, additional, Zhang, Haiwu, additional, Zhang, Jiandi, additional, and Zhou, H., additional

Published
2022
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13. Tailoring of Colloidal HfO2 Nanocrystals with Unique Morphologies and New Self‐Assembly Features.

Author

Ohlerth, Thorsten, Du, Hongchu, Hammoor, Thomas, Mayer, Joachim, and Simon, Ulrich

Abstract

Advancing the synthesis of HfO2 nanocrystals, a refined anhydrous protocol that enables kinetic trapping of the metastable tetragonal phase and modulates twinning defects in anisotropically grown monoclinic nanoprisms is presented. This evolved sol–gel approach examines the role of the capping agent tri‐n‐octylphosphine oxide (TOPO) and introduces a novel heating strategy with sequential growth stages. Replacement of TOPO with triphenylphosphine oxide (TPPO) leads to the formation of prismatic hafnia nanocrystals exhibiting pristine {011}‐facets of the monoclinic phase. Furthermore, a hot‐injection inspired heating approach yields sub‐4 nm isotropic HfO2 nanocrystals in the tetragonal phase, bypassing the need for aliovalent cation species. In contrast, a heat‐up approach culminates in the generation of well‐characterized HfO2 nanorods. With sophisticated transmission electron microscopy analysis and the Wulff construction method, insights into the structural nucleation of nanoparticle growth are provided. This synthesis offers exceptional control and facilitates the formation of self‐assemblies akin to liquid crystals, opening the door for new applications with nanocolloidal HfO2. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Towards Three-dimensional Mapping of Skyrmionic Spin Textures in an FeGe Nanodisk Using Off-axis Electron Holography

Author

Zheng, Fengshan, primary, Caron, Jan, additional, Savchenko, Andrii S, additional, Wang, Shasha, additional, Wang, Weiwei, additional, Denneulin, Thibaud, additional, Kovács, András, additional, Du, Hongchu, additional, Du, Haifeng, additional, Kiselev, Nikolai S, additional, Blügel, Stefan, additional, and Dunin-Borkowski, Rafal E, additional

Published
2023
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21. Atomic-Scale Insights into Nickel Exsolution on LaNiO3 Catalysts via In Situ Electron Microscopy

Author

Cao, Pengfei, primary, Tang, Pengyi, additional, Bekheet, Maged F., additional, Du, Hongchu, additional, Yang, Luyan, additional, Haug, Leander, additional, Gili, Albert, additional, Bischoff, Benjamin, additional, Gurlo, Aleksander, additional, Kunz, Martin, additional, Dunin-Borkowski, Rafal E., additional, Penner, Simon, additional, and Heggen, Marc, additional

Published
2021
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27. Antiphase Boundaries Constitute Fast Cation Diffusion Paths in SrTiO3 Memristive Devices

Author

Heisig, Thomas, primary, Kler, Joe, additional, Du, Hongchu, additional, Baeumer, Christoph, additional, Hensling, Felix, additional, Glöß, Maria, additional, Moors, Marco, additional, Locatelli, Andrea, additional, Menteş, Tevfik Onur, additional, Genuzio, Francesca, additional, Mayer, Joachim, additional, De Souza, Roger A., additional, and Dittmann, Regina, additional

Published
2020
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30. Changing the Phosphorus Allotrope from a Square Columnar Structure to a Planar Zigzag Nanoribbon by Increasing the Diameter of Carbon Nanotube Nanoreactors

Author

Zhang, Jinying, primary, Fu, Chengcheng, additional, Song, Shixin, additional, Du, Hongchu, additional, Zhao, Dan, additional, Huang, Hongyang, additional, Zhang, Lihui, additional, Guan, Jie, additional, Zhang, Yifan, additional, Zhao, Xinluo, additional, Ma, Chuansheng, additional, Jia, Chun-Lin, additional, and Tománek, David, additional

Published
2020
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33. Local crystallographic shear structures in a [201] extended mixed dislocations of SrTiO₃ unraveled by atomic-scale imaging using transmission electron microscopy and spectroscopy

Author

Du, Hongchu, Jia, Chunlin, and Mayer, Joachim

Subjects
ddc:540
Abstract

Recently, extended mixed dislocations were observed at a [001]/(100) low-angle tilt grain boundary of a SrTiO3 bicrystal because of a slight twist between the two crystal parts. The b = a[201]/(100) mixed dislocations at the grain boundary dissociate into three dislocations with Burgers vector b of a/2[101], a[100], and a/2[101], respectively. A structure model has been proposed in particular for the dislocation cores of the two partials with b = a/2[101] based on the high-angle annular dark-field (HAADF) images acquired by scanning transmission electron microscopy (STEM). However, the details of the atomic structure and the chemical composition of the dislocation cores remain unexplored, especially for the b = a[100] dislocation that is evidently disassociated into two b = a/2[101] partial dislocations. In this work, we study the further atomic details of the extended mixed dislocations, in particular the local chemistry, in a SrTiO3 bicrystal using STEM, electron energy loss spectroscopy (EELS), and energy dispersive X-ray (EDX) spectroscopy techniques. By these atomic-scale imaging techniques, we reveal a unique feature for the atomic structure of the b = a[201]/(100) extended mixed dislocation, which we named as local crystallographic shear (LCS) structures. In addition, we identify a rock salt FCC-type TiOx (x = 0.66–1.24) phase at the locations of the extended mixed dislocations. In contrast to the insulating TiO2 phases, the TiOx phase is known to exhibit very low electrical resistivity of only several μΩ cm. In this regard, the extended mixed dislocations of SrTiO3 comprising the FCC TiOx phase may function as the conducting filament in resistive switching processes by completion and disruption of the TiOx phase along the dislocation cores through electrically stimulated redox reactions.

Published
2019

34. On Oxidation Resistance Mechanisms at 1273 K of Tungsten-Based Alloys Containing Chromium and Yttria

Author

Klein, Felix, Wegener, Tobias, Breuer, Uwe, Litnovsky, Andrey, Rasinski, Marcin, Tan, Xiaoyue, Schmitz, Janina, Linsmeier, Christian, Coenen, Jan Willem, Du, Hongchu, and Mayer, Joachim

Subjects
oxidation resistance, lcsh:TN1-997, diffusion, technology, industry, and agriculture, magnetron thin films, equipment and supplies, yttria, yttrium, ddc:530, isotope tracer, W-based alloys, DEMO, lcsh:Mining engineering. Metallurgy, W-Cr-Y alloys
Abstract

Tungsten (W) is currently deemed the main candidate for the plasma-facing armor material of the first wall of future fusion reactors, such as DEMO. Advantages of W include a high melting point, high thermal conductivity, low tritium retention, and low erosion yield. However, was an accident to occur, air ingress into the vacuum vessel could occur and the temperature of the first wall could reach 1200K to 1450K due to nuclear decay heat. In the absence of cooling, the temperature remains in that range for several weeks. At these temperatures, the radioactive tungsten oxidizes and then volatilizes. Smart W alloys are therefore being developed. Smart alloys are supposed to preserve properties of W during plasma operation while suppressing tungsten oxide formation in case of an accident. This study focuses on investigations of thin film smart alloys produced by magnetron sputtering. These alloys provide an idealistic system with a homogeneous distribution of the elements W, chromium (Cr), and yttrium (Y) on an atomic scale. The recommended composition is W with 12 weight % of Cr and 0.5 weight % of Y. Passivation and a suppression of WO3 sublimation is shown. For the first time, the mechanisms yielding the improved oxidation resistance are analyzed in detail. A protective Cr2O3 layer forms at the surface. The different stages of the oxidation processes up to the failure of the protective function are analyzed for the first time. Using 18O as a tracer, it is shown for the first time that the oxide growth occurs at the surface of the protective oxide. The Cr is continuously replenished from the bulk of the sample, including the Cr-rich phase which forms during exposure at 1273K. A homogenous distribution of yttria within the W-matrix, which is preserved during oxidation, is a peculiarity of the analyzed alloy. Further, an Y-enriched nucleation site is found at the interface between metal and oxide. This nucleation sites are deemed to be crucial for the improved oxidation resistance.

Published
2018

35. Au Nanoparticles as Template for Defect Formation in Memristive SrTiO3 Thin Films

Author

Raab, Nicolas, Schmidt, Dirk Oliver, Du, Hongchu, Kruth, Maximilian, Simon, Ulrich, and Dittmann, Regina

Subjects
lcsh:Chemistry, TheoryofComputation_MATHEMATICALLOGICANDFORMALLANGUAGES, lcsh:QD1-999, resistive switching, memristive devices, ddc:540, SrTiO3, Au nanoparticles, memristor
Abstract

Nanomaterials 8(11), 869 (2018). doi:10.18154/RWTH-2019-00092 special issue: "Special Issue "Nanoscale Surface Engineering" / Guest Editor Dr. Stéphane Mornet, Dr. Glenna Drisko", Published by MDPI, Basel

Published
2018

39. Layer‐Switching Mechanisms in Sb 2 Te 3

Author

Wang, Jiang-Jing, primary, Wang, Jun, additional, Xu, Yazhi, additional, Xin, Tianjiao, additional, Song, Zhitang, additional, Pohlmann, Marc, additional, Kaminski, Marvin, additional, Lu, Lu, additional, Du, Hongchu, additional, Jia, Chun-Lin, additional, Mazzarello, Riccardo, additional, Wuttig, Matthias, additional, and Zhang, Wei, additional

Published
2019
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43. Valence change ReRAMs (VCM) - Experiments and modelling: general discussion

Author

Aono, Mazakazu, primary, Baeumer, Christoph, additional, Bartlett, Philip, additional, Brivio, Stefano, additional, Burr, Geoffrey, additional, Burriel, Monica, additional, Carlos, Emanuel, additional, Deswal, Sweety, additional, Deuermeier, Jonas, additional, Dittmann, Regina, additional, Du, Hongchu, additional, Gale, Ella, additional, Hambsch, Sebastian, additional, Hilgenkamp, Hans, additional, Ielmini, Daniele, additional, Kenyon, Anthony J., additional, Kiazadeh, Asal, additional, Kindsmüller, Andreas, additional, Kissling, Gabriela, additional, Köymen, Itir, additional, Menzel, Stephan, additional, Pla Asesio, Dolors, additional, Prodromakis, Themis, additional, Santamaria, Monica, additional, Shluger, Alexander, additional, Thompson, Damien, additional, Valov, Ilia, additional, Wang, Wei, additional, Waser, Rainer, additional, Williams, R. Stanley, additional, Wrana, Dominik, additional, Wouters, Dirk, additional, Yang, Yuchao, additional, and Zaffora, Andrea, additional

Published
2019
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46. Antiphase Boundaries Constitute Fast Cation Diffusion Paths in SrTiO3 Memristive Devices.

Author

Heisig, Thomas, Kler, Joe, Du, Hongchu, Baeumer, Christoph, Hensling, Felix, Glöß, Maria, Moors, Marco, Locatelli, Andrea, Menteş, Tevfik Onur, Genuzio, Francesca, Mayer, Joachim, De Souza, Roger A., and Dittmann, Regina

Subjects
ANTIPHASE boundaries, METAL-insulator-metal structures, DIFFUSION, ELECTRICAL conductivity transitions, TRANSMISSION electron microscopy
Abstract

Resistive switching in transition metal oxide‐based metal‐insulator‐metal structures relies on the reversible drift of ions under an applied electric field on the nanoscale. In such structures, the formation of conductive filaments is believed to be induced by the electric‐field driven migration of oxygen anions, while the cation sublattice is often considered to be inactive. This simple mechanistic picture of the switching process is incomplete as both oxygen anions and metal cations have been previously identified as mobile species under device operation. Here, spectromicroscopic techniques combined with atomistic simulations to elucidate the diffusion and drift processes that take place in the resistive switching model material SrTiO3 are used. It is demonstrated that the conductive filament in epitaxial SrTiO3 devices is not homogenous but exhibits a complex microstructure. Specifically, the filament consists of a conductive Ti3+‐rich region and insulating Sr‐rich islands. Transmission electron microscopy shows that the Sr‐rich islands emerge above Ruddlesden–Popper type antiphase boundaries. The role of these extended defects is clarified by molecular static and molecular dynamic simulations, which reveal that the Ruddlesden–Popper antiphase boundaries constitute diffusion fast‐paths for Sr cations in the perovskites structure. [ABSTRACT FROM AUTHOR]

Published
2020
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48. Genesis and Effects of Swapping Bilayers in Hexagonal GeSb2Te4

Author

Wang, Jiang-Jing, primary, Wang, Jun, additional, Du, Hongchu, additional, Lu, Lu, additional, Schmitz, Peter C., additional, Reindl, Johannes, additional, Mio, Antonio M., additional, Jia, Chun-Lin, additional, Ma, Evan, additional, Mazzarello, Riccardo, additional, Wuttig, Matthias, additional, and Zhang, Wei, additional

Published
2018
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49. Oxygen Exchange Processes between Oxide Memristive Devices and Water Molecules

Author

Heisig, Thomas, primary, Baeumer, Christoph, additional, Gries, Ute N., additional, Mueller, Michael P., additional, La Torre, Camilla, additional, Luebben, Michael, additional, Raab, Nicolas, additional, Du, Hongchu, additional, Menzel, Stephan, additional, Mueller, David N., additional, Jia, Chun-Lin, additional, Mayer, Joachim, additional, Waser, Rainer, additional, Valov, Ilia, additional, De Souza, Roger A., additional, and Dittmann, Regina, additional

Published
2018
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