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- ItemHow to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation(Bristol : IOP Publishing, 2023) Lünser, Klara; Undisz, Andreas; Nielsch, Kornelius; Fähler, SebastianUnderstanding the martensitic microstructure in nickel-titanium (NiTi) thin films helps to optimize their properties for applications in microsystems. Epitaxial and single-crystalline films can serve as model systems to understand the microstructure, as well as to exploit the anisotropic mechanical properties of NiTi. Here, we analyze the growth of NiTi on single-crystalline MgO(100) and Al2O3(0001) substrates and optimize film and buffer deposition conditions to achieve epitaxial films in (100)- and (111)-orientation. On MgO(100), we compare the transformation behavior and crystal quality of (100)-oriented NiTi films on different buffer layers. We demonstrate that a vanadium buffer layer helps to decrease the low-angle grain boundary density in the NiTi film, which inhibits undesired growth twins and leads to higher transformation temperatures. On Al2O3(0001), we analyze the orientation of a chromium buffer layer and find that it grows (111)-oriented only in a narrow temperature range around 500 ∘C. By depositing the Cr buffer below the NiTi film, we can prepare (111)-oriented, epitaxial films with transformation temperatures above room temperature. Transmission electron microscopy confirms a martensitic microstructure with Guinier Preston-zone precipitates at room temperature. We identify the deposition conditions to approach the ideal single crystalline state, which is beneficial for the analysis of the martensitic microstructure and anisotropic mechanical properties in different film orientations.
- ItemMXenes and the progress of Li–S battery development - a perspective(Bristol : IOP Publishing, 2021) Balach, Juan; Giebeler, LarsLithium–sulfur (Li–S) battery has attracted tremendous interest owing to its high energy density at affordable costs. However, the irreversible active material loss and subsequent capacity fading caused by the uncontrollable shuttling of polysulfides have greatly hampered its commercial viability. MXenes, a novel class of 2D materials derived from nano-layered MAX phases, have been shown the potential to push the development of sulfur-based batteries to a next level owing to their high conductivity, strong polysulfide affinity and electrocatalytic properties. This perspective article focuses on the possible implications that MXene-based materials will have in the development of advanced sulfur-based batteries and their potential application in different upcoming technologies. In four sections possible developments are outlined which can be reached in the next 10 years, that enable a highly reliable, minimized Li–S battery finally combined with energy harvesters to fabricate autonomous power supplies for the next generation of microscaled devices like meteorological or geotechnical probes, wearable (medical) sensors or other suitable mobile devices. Finally, a flowchart illustrates the possible way to realize some important milestones for the certain possible steps with significant contributions of MXenes.
- ItemRoadmap on commercialization of metal halide perovskite photovoltaics(Bristol : IOP Publishing, 2023) Feng, Shien-Ping; Cheng, Yuanhang; Yip, Hin-Lap; Zhong, Yufei; Fong, Patrick W. K.; Li, Gang; Ng, Annie; Chen, Cong; Castriotta, Luigi Angelo; Matteocci, Fabio; Vesce, Luigi; Saranin, Danila; Carlo, Aldo Di; Wang, Puqun; Wei Ho, Jian; Hou, Yi; Lin, Fen; Aberle, Armin G; Song, Zhaoning; Yan, Yanfa; Chen, Xu; Yang, Yang (Michael); Syed, Ali Asgher; Ahmad, Ishaq; Leung, Tiklun; Wang, Yantao; Lin, JingYang; Ng, Alan Man Ching; Li, Yin; Ebadi, Firouzeh; Tress, Wolfgang; Richardson, Giles; Ge, Chuangye; Hu, Hanlin; Karimipour, Masoud; Baumann, Fanny; Tabah, Kenedy; Pereyra, Carlos; Raga, Sonia R.; Xie, Haibing; Lira-Cantu, Monica; Khenkin, Mark V.; Visoly-Fisher, Iris; Katz, Eugene A.; Vaynzof, Yana; Vidal, Rosario; Yu, Guicheng; Lin, Haoran; Weng, Shuchen; Wang, Shifeng; Djurišić, Aleksandra B.Perovskite solar cells (PSCs) represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of the relevant physics of the devices and issues which affect their efficiency and stability, there are still unresolved problems and obstacles on the path toward commercialization of this promising technology. In this roadmap, we aim to provide a concise and up to date summary of outstanding issues and challenges, and the progress made toward addressing these issues. While the format of this article is not meant to be a comprehensive review of the topic, it provides a collection of the viewpoints of the experts in the field, which covers a broad range of topics related to PSC commercialization, including those relevant for manufacturing (scaling up, different types of devices), operation and stability (various factors), and environmental issues (in particular the use of lead). We hope that the article will provide a useful resource for researchers in the field and that it will facilitate discussions and move forward toward addressing the outstanding challenges in this fast-developing field.
- ItemImpact of atomic defects in the electronic states of FeSe1-x Sx superconducting crystals(Bristol : IOP Publishing, 2022) Aragón Sánchez, Jazmín; Amigó, María Lourdes; Belussi, Cristian Horacio; Ale Crivillero, María Victoria; Suárez, Sergio; Guimpel, Julio; Nieva, Gladys; Gayone, Julio Esteban; Fasano, YaninaThe electronic properties of Fe-based superconductors are drastically affected by deformations on their crystal structure introduced by doping and pressure. Here we study single crystals of FeSe 1 − x Sx and reveal that local crystal deformations such as atomic-scale defects impact the spectral shape of the electronic core level states of the material. By means of scanning tunneling microscopy we image S-doping induced defects as well as diluted dumbbell defects associated with Fe vacancies. We have access to the electronic structure of the samples by means of x-ray photoemission spectroscopy (XPS) and show that the spectral shape of the Se core levels can only be adequately described by considering a principal plus a minor component of the electronic states. We find this result for both pure and S-doped samples, irrespective that in the latter case the material presents extra crystal defects associated to doping with S atoms. We argue that the second component in our XPS spectra is associated with the ubiquitous dumbbell defects in FeSe that are known to entail a significant modification of the electronic clouds of surrounding atoms.
- ItemOrigin and avoidance of double peaks in the induced voltage of a thermomagnetic generator for harvesting low-grade waste heat(Bristol : IOP Publishing, 2022) Dzekan, Daniel; Kischnik, Tim D.; Diestel, Anett; Nielsch, Kornelius; Fähler, SebastianThermomagnetic harvesting is an emerging approach used to convert low-grade waste heat to electricity, which recently obtained a boost due to the development of both more efficient functional materials and innovative device concepts. Here, we examine a thermomagnetic generator which utilizes gadolinium as the thermomagnetic material and report on the double peaks of the induced voltage. Using a combination of experiments and theory we show that these double peaks originate from the interaction between an asymmetric magnetization curve and a pretzel-like magnetic field topology. Double peaks are detrimental for the output power and can be avoided by matching the magnetization change by adjusting the cold and hot fluid flow.
- ItemSpin Nernst effect in a p-band semimetal InBi(Bristol : IOP Publishing, 2020) Zhang, Yang; Xu, Qiunan; Koepernik, Klaus; Fu, Chenguang; Gooth, Johannes; van den Brink, Jeroen; Felser, Claudia; Sun, YanSince spin currents can be generated, detected, and manipulated via the spin Hall effect (SHE), the design of strong SHE materials has become a focus in the field of spintronics. Because of the recent experimental progress also the spin Nernst effect (SNE), the thermoelectrical counterpart of the SHE, has attracted much interest. Empirically strong SHEs and SNEs are associated with d-band compounds, such as transition metals and their alloys—the largest spin Hall conductivity (SHC) in a p-band material is $\sim 450\left(\hslash /e\right){\left({\Omega}\enspace \mathrm{c}\mathrm{m}\right)}^{-1}$ for a Bi–Sb alloy, which is only about a fifth of platinum. This raises the question whether either the SHE and SNE are naturally suppressed in p-bands compounds, or favourable p-band systems were just not identified yet. Here we consider the p-band semimetal InBi, and predict it has a record SHC ${\sigma }_{xy}^{z}\approx 1100\enspace \left(\hslash /e\right){\left({\Omega}\enspace \mathrm{c}\mathrm{m}\right)}^{-1}$ which is due to the presence of nodal lines in its band structure. Also the spin-Nernst conductivity ${\alpha }_{zx}^{y}\approx 1.2\enspace \left(\hslash /e\right)\left(A/m\cdot K\right)$ is very large, but our analysis shows its origin is different as the maximum appears in a different tensor element compared to that in SHC. This insight gained on InBi provides guiding principles to obtain a strong SHE and SNE in p-band materials and establishes a more comprehensive understanding of the relationship between the SHE and SNE.