materials research – Page 5 of 5 – Blog • by NanoWorld®

Topological objects and defects (e.g. skyrmions, domain walls, vortices,) in condensed matters have attracted a lot of interest as a field for exploring emerging exotic phenomena and functionalities.*

In materials with ferroic order, these topological objects can also be manipulated and controlled by external fields without disrupting their host lattice, making them promising elemental building blocks for potential configurable topological nanoelectronics. *

Ferroelectric topological objects provide a promising area for investigating emerging physical properties that could potentially be utilized in future nanoelectronic devices. *

In the article “Quasi-one-dimensional metallic conduction channels in exotic ferroelectric topological defects” Wenda Yang, Guo Tian, Yang Zhang, Fei Xue, Dongfeng Zheng, Luyong Zhang, Yadong Wang, Chao Chen, Zhen Fan, Zhipeng Hou, Deyang Chen, Jinwei Gao, Min Zeng, Minghui Qin, Long-Qing Chen, Xingsen Gao and Jun-Ming Liu demonstrate the existence of metallic conduction superfine (<3 nm) channels in two types of exotic topological defects, namely a quadrant vortex core or simply vortex core and a quadrant center domain core or simply center core, in an array of BiFeO3 (BFO) nanoislands.*

The authors discover via the phase-field simulation that the superfine metallic conduction channels along the center cores arise from the screening charge carriers confined at the core region, whereas the high conductance of vortex cores results from a field-induced twisted state. These conducting channels can be reversibly created and deleted by manipulating the two topological states via electric field, leading to an apparent electroresistance effect with an on/off ratio higher than 103.*

The findings by Wenda Yang et al. open up the possibility of using these functional one-dimensional topological objects in high-density nanoelectronic devices, e.g. nonvolatile memory.*

NanoWorld PlatinumIdridium5 coated Arrow-EFM AFM probes were used to examine the domain structures by vector piezoresponse force microscopy (PFM). By using vector PFM mode, the authors could simultaneously map the vertical and lateral piezoresponse signals from the nanoisland one by one.*

NanoWorld Conductive Diamond coated AFM probes CDT-NCHR were used for the conductive current distribution maps, current–voltage (I–V) measurements that were characterized by conductive atomic force microscopy (C-AFM).

Fig. 2 from “*Quasi-one-dimensional metallic conduction channels in exotic ferroelectric topological defects*” by Wenda Yang et al.:
**The domain structures and corresponding conductive properties for both a vortex and a center topological states confined in two nanoislands**.
a, b PFM and C-AFM images for both a vortex state (a) and a center state (b), the micrographs from the left to the right are PFM vertical phase images illustrating the uniform upward vertical polarization components for both nanoislands, the PFM lateral phase images recorded at sample rotation of 0o and 90o to evaluate the directions of lateral polarization components respectively along x axis ([100] axis) and y axis ([100] axis), the lateral polarization vector direction maps derived from the PFM data, and corresponding C-AFM maps. The thick arrows aside the PFM images mark the directions of the cantilever for each PFM scan, and the fine arrows inside the images mark the directions of polarization components perpendicular to the directions of the cantilever. c, d Extracted current spatial profiles from the C-AFM maps for both the vortex (c) and the center (d) cores, extracted from a and b, respectively. The inserts in c and d illustrate the C-AFM maps and schematic local polarization configurations for the two topological cores. e Temperature-dependent conductive current (I–V) curves for both topological cores and domain walls.*

*Wenda Yang, Guo Tian, Yang Zhang, Fei Xue, Dongfeng Zheng, Luyong Zhang, Yadong Wang, Chao Chen, Zhen Fan, Zhipeng Hou, Deyang Chen, Jinwei Gao, Min Zeng, Minghui Qin, Long-Qing Chen, Xingsen Gao and Jun-Ming Liu
Quasi-one-dimensional metallic conduction channels in exotic ferroelectric topological defects
Nature Communications volume 12, Article number: 1306 (2021)
DOI: https://doi.org/10.1038/s41467-021-21521-9

Please follow this external link to read the full article: https://rdcu.be/cg0JY

Open Access : The article “Quasi-one-dimensional metallic conduction channels in exotic ferroelectric topological defects” by Wenda Yang, Guo Tian, Yang Zhang, Fei Xue, Dongfeng Zheng, Luyong Zhang, Yadong Wang, Chao Chen, Zhen Fan, Zhipeng Hou, Deyang Chen, Jinwei Gao, Min Zeng, Minghui Qin, Long-Qing Chen, Xingsen Gao and Jun-Ming Liu is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Because of the global climate change, energy-saving and sustainable technologies are becoming more and more important. Therefore, the demands on technologies for the conversion, storage and use of renewable energies are constantly growing. *

The building sector plays an important role in terms of energy saving potential. *

In particular, the class of so-called smart windows offers an approach to save energy in the building sector by efficiently regulating incident light. *

Chromogenic thin films are crucial building blocks in smart windows to modulate the flux of visible light and heat radiation into buildings. *

Due to their diversity in composition and structure as well as their superior performance, electrochromism based on thin film transition metal oxides has become increasingly important in the last decade. *

Electrochromic materials such as tungsten oxide are well established in those devices. Sputter deposition offers a well-suited method for the production of such layers, which can also be used on an industrial scale. *

The EC properties of tungsten oxide layers depend on the composition, the crystal structure and the morphology. *

The film characteristics are strongly dependent on the growth technique. *

In the article “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity describe how Tungsten oxide thin films were grown by ion-beam sputter deposition (IBSD), a less common sputtering variant. *

They then show the possibility of influencing technologically relevant samples characteristics by using different preparation parameters (e.g., gas mixture or growth temperature). This allows to tune the elemental composition, optical properties or to influence the structure and the degree of crystallization in the resulting thin films. *

The high reproducibility as well as the high purity of IBSD-grown layers render ion-beam sputter deposition a suitable candidate for growth of tungsten oxide and, most likely, other chromogenic materials. *

Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were conducted to analyze the crystallite surface structure.

For the AFM investigations in air NanoWorld® Pointprobe® SEIHR AFM probes designed for soft non-contact mode imaging were used. (typical resonance frequency 130 kHz, typical force constant 15 N/m ). *

Figure 2 g, h and i from "Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition" by Miario Gies et al. In Fig. 2 g, the surface of a sample deposited at RT and a moderate O2 flux of 5.15 sccm is shown as analyzed by Atomic Force Microscopy ( AFM ). Individual grains of about 0.2 μm size appear interconnected without sharply defined grain boundaries. The root-mean-square surface roughness was determined to be around 9 nm. In comparison, Fig. 2h shows the morphology of a sample synthesized at RT under oxygen-poor conditions. Again, no sharply defined grains are recognizable. However, the grains seem to be a bit more extended. The determined roughness of the surface is approximately 7 nm. At an increased deposition temperature of 400 ∘C, larger round-shaped grains of about 0.5 μm lateral expansion were obtained, cf. Fig. 2i, leading to an increased roughness of around 20 nm, much higher than for the unheated samples. NanoWorld Pointprobe SEIHR AFM probes were used. — Figure 2 g, h and i from “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” by Mario Gies et al.:
AFM images of samples, deposited at room temperature under a moderate O2 flux of 5.15 sccm (g) and under oxygen-poor conditions (h). Compared to the surface of a sample grown at 400 ∘C (i), the surface roughness is significantly smoother. For the full figure please refer to the full article: https://link.springer.com/article/10.1007/s10853-020-05321-y

*Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity
Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition
Journal of Materials Science (2020)
DOI: https://doi.org/10.1007/s10853-020-05321-y

Please follow this external link to read the full article: https://link.springer.com/article/10.1007/s10853-020-05321-y

Open Access : The article “Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition” by Mario Gies, Fabian Michel, Christian Lupó, Derck Schlettwein, Martin Becker and Angelika Polity is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.