*Pressemitteilung* ,,Mit winzigen Nanopartikeln zu besserem Ladungstransport (Nr. 75/2021)" Von Sepideh Izadi und Prof. Dr. Gabi Schierning Zur Pressemitteilung
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Dr. Lauritz Ule Schnatmann
ERC Consolidator Grant 2019
Funding period: 01.06.2020-31.05.2025
Ever since the discovery of topological surface states in three-dimensional (3D) topological insulators (TI), this fascinating physics has thrilled scientists. While arguable the transport properties of 3D TIs are of utmost importance for potential applications, they are extremely difficult to characterize, yet utilize for devices. The reason is that transport in those materials is always dominated by bulk carriers. Within this proposed research project, I will overcome the problem of bulk carrier domination conceptually by a nanoparticle-based materials’ design of interrupted early stage sintering. By this interrupted early stage sintering approach, I compact 3D TI nanoparticles at mild temperature and low pressure. The obtained highly porous macroscopic sample features a carrier density of the surface states in the order of 1018 cm-3, hence in a comparable order of magnitude as the bulk carrier density. Further, the interruptedly sintered nanoparticles impose energetic barriers for the transport of bulk carriers (hopping transport), while the connected surfaces of the nanoparticles provide a 3D percolation path for surface carriers. Within the preliminary work, my group tuned interruptedly sintered nanoparticles into a transport regime completely dominated by the surface states.
Within this project, nanoparticle-based macroscopic 3D TI materials will be developed towards test structures for devices. Their properties will be tailored by the nanoparticle synthesis (Objective 1) and the materials processing of interrupted early stage sintering (Objective 2). This is complemented by an in-depth characterization of the transport as well as spectroscopic properties and data modelling (Objective 3). My group will use this know-how for the fabrication of test devices (Objective 4). This combination will provide the first macroscopic quantum transport devices that utilize the unique electronic properties of surface states, overcoming the problem of bulk carrier domination.
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme. Grant agreement No. 863823.
Funding period: 10.2021 - 09.2024
For the internet of things (IoT) in general and medical sensors in particular, low power wireless data transmitters are required. Up to date, most of such transmitters require batteries or inefficient radio frequency (RF) harvesting.
In THAWIT, we want to investigate and demonstrate the first wireless data transmitter, which can be supplied by means of compact integrated thermoelectric harvesting. To allow supply-autarkic operation, we have to meet the following challenges. The power consumption of the transmitter must be massively reduced. Moreover, the power density of the thermoelectric devices must be increased. A major challenge is the capability for integration on silicon limiting the possible material compositions. We want to develop silicon-compatible harvesting elements with a power density beyond 10 μW/mm2 at a moderate temperature difference of 7 K. To meet this challenge, we rigorously optimise the geometry and material compositions. A high thermoelectric leg height is necessary for high output power density, affecting the choice of the photoresist and deposition parameters of the thermoelectric material. A new process for the p-type thermoelectric leg is researched to reduce the thermal conductivity. In addition, we develop a silicon-compatible micro-supercapacitor serving as energy buffer. To enable compatibility with the fabrication technology and equipment at IFW, we realize it by a high-performance all-solid-state interdigital in-plane micro-supercapacitor. It is based on photo-lithographically patterned sputtered electrodes and a solid electrolyte.
Considering energy saving losses and component areas of 2 mm2, the CMOS transmitter must operate with a dc power of around 10 μW. To enable such an ultra-low dc power, we study direct modulated oscillators with aggressive duty-cycling of around 0.1 %, fast ramp-up and miniaturized leakage in the sleep phases. In addition to impedance-matched antennas requiring buffer amplifiers, we consider also inductive antennas which can be directly incorporated in the LC-resonator of the oscillator. A textile-compatible woven or printed antenna is designed for the demonstrator. The demonstrator shall operate according to the medical implant communication service (MICS). The final goal is to show data transmission around 400 MHz with a data rate of 1-10 kb/s for distances of up to 1 meter. THAWIT combines the complementary competences of Gabi Schierning, IFW, in the area of thermoelectric devices, and Frank Ellinger, TUD regarding low power integrated RF circuits.
This project has received funding from the Deutsche Forschungsgemeinschaft (DFG) under grand number SCHI 1010/12-1.
Förderperiode: 04.2022 - 03.2024
Abfallprodukte der Silizium-Solarwafer- und Halbleiter-Fertigung bzw. -Anwendung werden verwendet, um diese durch nachgeschaltete Prozessschritte für den Einsatz in verschiedenen Anwendungen wie Lithium-Ionen-Batterien, Dioden, Thermoelektrik oder Hockleistungskeramiken zu ertüchtigen.
Der Fokus liegt auf dem Material- und Verfahrens-Aspekt:
Das Material muss im Hinblick auf die Weiterverarbeitung eingehend charakterisiert werden. Diese erfolgt in einem Gasphasenreaktor zur Nanomaterial-Herstellung. Die kontinuierliche Förderung von großen Pulvermengen stellt dabei eine verfahrenstechnische Herausforderung dar. Im Reaktor wird das Material z.T. von Verunreinigungen befreit und ggf. dotiert. Das entstandene Material wird mittels Laser-Strahlschmelzen (LBPF) zu Demonstratoren verarbeitet, die elektrisch charakterisiert werden, um ihre Verwendbarkeit für die o.g. Anwendungen zu verifizieren.
Neben dem volkswirtschaftlichen Gesamtnutzen können insbesondere Unternehmen aus den Bereichen PV-Recycling, Anlagenbau, Materialaufbereitung sowie LBPF-Endanwender unmittelbar profitieren, indem sie ihr bestehendes Fertigungs- und Produktportfolio um entsprechende Technologien und Komponenten erweitern. Typischerweise sind diese Segmente häufig durch KMU geprägt: Reaktoren zur Nanomaterialsynthese, wie sie in diesem Vorhaben zum Einsatz kommen, liegen im Aufgabenbereich von Anlagenbauern im KMU-Sektor, ebenso wie die Auslegung und Produktion eines Pulverförderers. LBPF-Prozesse ermöglichen die zeitnahe Bereitstellung von Funktionsprototypen und die endkonturnahe Herstellung komplexer Bauteile (mit entsprechender Funktionsintegration), die mittels konventioneller Fertigungstechnologien nur schwer oder nicht hergestellt werden können. Daraus ergibt sich insbesondere für KMU das Potenzial, dass Versorgungsketten flexibilisiert, Lagerkosten reduziert und Lieferengpässe bestimmter Produkte überbrückbar sind. Eine leistungsfähige On-Demand-Fertigung ist die Folge.
Die komplette Puplikationsliste finden Sie hier.
The role of electrons during the martensitic phase transformation in NiTi-based shape memory alloys Alexander Kunzmann, Jan Frenzel, Ulrike Wolff, Jeong Woo Han, Lars Giebeler, David Piorunek, Martin Mittendorff, Juliane Scheiter, Heiko Reith, Nicolas Perez, Kornelius Nielsch, Gunther Eggeler, Gabi Schierning Materialstoday Physics
"Nickel-titanium (Ni50Ti50)-based alloys are the most important representatives of the class of shape memory alloys. However, the role of electrons in this transformation leading to the shape memory effect is not yet overall understood. Here we show how the alloy composition affects resistivity, Hall coefficient and Seebeck coefficient as well as Terahertz reflectance during the martensitic phase transformation. Remarkably, the charge carrier density obtained by Hall measurements is reduced by almost one order of magnitude in the martensitic phase compared to the austenitic phase, and its reduction starts well before the actual transformation. This reduction of the charge carrier concentration is also seen in the obtained Terahertz spectra. Together with this reduction of the charge carrier density, the charge carrier mobility increases at the phase transformation. This means that neither additional scattering events nor altered electron-phonon coupling play a dominant role for the interpretation of the anomaly in the electrical resistivity. We further utilize these transport data to deduce the electronic entropy contribution to this phase transformation and compare it to the total entropy contribution obtained by heat capacity measurements. The electronic entropy contribution directly scales with the martensitic start temperature and reaches over 30 % of the total entropy contribution for compositions close to equiatomic Ni50Ti50. The experimental data points towards a partly transfer of electron density from the free electron gas (austenite) to the bonding (martensite). We interpret this in terms of a formation of a charge density wave phase that would fit to both findings, the strong reduction of charge carriers, as well as the high electronic entropy contribution to this phase transformation."
Towards tellurium-free thermoelectric modules for power generation from low-grade heat.
Ying P, He R, Mao J, Zhang Q, Reith H, Sui J, Ren Z, Nielsch K, Schierning G (2021)
Nature communications 12(1): 1121
"Thermoelectric technology converts heat into electricity directly and is a promising source of clean electricity. Commercial thermoelectric modules have relied on Bi2Te3-based compounds because of their unparalleled thermoelectric properties at temperatures associated with low-grade heat (<550 K). However, the scarcity of elemental Te greatly limits the applicability of such modules. Here we report the performance of thermoelectric modules assembled from Bi2Te3-substitute compounds, including p-type MgAgSb and n-type Mg3(Sb,Bi)2, by using a simple, versatile, and thus scalable processing routine. For a temperature difference of ~250 K, whereas a single-stage module displayed a conversion efficiency of ~6.5%, a module using segmented n-type legs displayed a record efficiency of ~7.0% that is comparable to the state-of-the-art Bi2Te3-based thermoelectric modules. Our work demonstrates the feasibility and scalability of high-performance thermoelectric modules based on sustainable elements for recovering low-grade heat."
Influence of Nanoparticle Processing on the Thermoelectric Properties of (BixSb1-X)(2)Te-3 Ternary Alloys
Salloum S, Bendt G, Heidelmann M, Loza K, Bayesteh S, Sepideh Izadi M, Kawulok P, He R, Schlorb H, Perez N, Reith H, et al. (2021)
ChemistryOpen 10(2): 189-198.
“The synthesis of phase-pure ternary solutions of tetradymite-type materials (BixSb1-x)(2)Te-3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated.“
Sepideh Izadi, Jeong Woo Han, Sarah Salloum, Ulrike Wolff, Lauritz Schnatmann, Aswin Asaithambi, Sebastian Matschy, Heike Schlörb, Heiko Reith, Nicolas Perez, Kornelius Nielsch, Stephan Schulz, Martin Mittendorff, Gabi Schierning: Interface-dominated topological transport in nanograined bulk Bi2Te3. Small (2021)
3D topological insulators (TI) host surface carriers with extremely high mobility. However, their transport properties are typically dominated by bulk carriers that outnumber the surface carriers by orders of magnitude. A strategy is herein presented to overcome the problem of bulk carrier domination by using 3D TI nanoparticles, which are compacted by hot pressing to macroscopic nanograined bulk samples. Bi2Te3 nanoparticles well known for their excellent thermoelectric and 3D TI properties serve as the model system. As key enabler for this approach, a specific synthesis is applied that creates nanoparticles with a low level of impurities and surface contamination. The compacted nanograined bulk contains a high number of interfaces and grain boundaries. Here it is shown that these samples exhibit metallic-like electrical transport properties and a distinct weak antilocalization. A downward trend in the electrical resistivity at temperatures below 5 K is attributed to an increase in the coherence length by applying the Hikami–Larkin–Nagaoka model. THz time-domain spectroscopy reveals a dominance of the surface transport at low frequencies with a mobility of above 103 cm2 V−1 s−1 even at room temperature. These findings clearly demonstrate that nanograined bulk Bi2Te3 features surface carrier properties that are of importance for technical applications.
|2002||Material Science and Engineering||University of Erlangen-Nürnberg||Dipl. Ing.|
|2005||Material Science and Engineering||University of Erlangen-Nürnberg||Dr.Ing.|
|2016||Materials for Electrical Engineering||University of Duisburg-Essen||Dr. Ing. habil.|
W2 TT W3 Professor for experimental physics, department of physics, University of Bielefeld, Germany
Head of group „Thermoelectric materials and devices“, in the Institute for Metallic Materials, Leibniz-Institute for solid state and materials science Dresden e.V. (IFW-Dresden), Germany, with director Prof. K. Nielsch
Leader of an independent young researcher group in the department of electrical engineering, University of Duisburg-Essen, Germany
Research assistant in the department of electrical engineering, University of Duisburg-Essen, Germany, with Prof. R. Schmechel
Research assistant in the Institute for Nanotechnology, Karlsruhe Institute of Technology (KIT), Germany, with director Prof. H. Hahn
|2005||Employee at Siemens Medical Solutions, Forchheim|
Research assistant in the department of materials science, Darmstadt Technical University, Germany, with Prof. H. von Seggern
Research internship in the school of chemical and physical sciences, Victoria University of Wellington, New Zealand, with Prof. A. Edgar
Research assistant in the department of materials science and engineering, University of Erlangen-Nürnberg, Germany, with Prof. A. Winnacker