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SnS Anodes with High Volumetric Capacity for Na‐ion Batteries and Their Characterization in Ether and Ester Electrolytes
No full textA current limitation to improving the volumetric energy density of Na‐ion batteries is the low density of the hard carbon(HC) anode. This problem can be solved by using high‐density, high‐capacity materials like SnS, which reacts with Na over a combined conversion and alloying reaction that theoretically provides 1022 mAh g −1 and 5335 mAh cc −1 (materials level). Here, composites containing SnS and thermally activated graphite(t‐G) are prepared by ball‐milling and tested with different electrolyte solutions. Adding 5 wt.% of t‐G is sufficient to obtain significant improvements in capacity and cycle life, reaching 608 mAh g −1 initially and 439 mAh g −1 after 100 cycles. Even without calendaring, the obtained volumetric capacity of 283 mAh cc −1 (electrode level) is already on‐par with commercial HC electrodes. Moreover, ether‐based electrolytes are found to be superior to ester‐based electrolytes, enabling high storage capacity and cycle life. The reaction is investigated by operando X‐ray diffraction and operando dilatometry. The inferior performance in ester‐based electrolytes is found to be due to a larger polarization that largely prevents the alloying reaction that occurs close to 0 V. Over cycling, the conversion reaction becomes gradually inactive while the alloying reaction shows a much better degree of reversibility.China Scholarship Council 10.13039/501100004543Helmholtz Association HGFChinese Government Scholarship 10.13039/501100010890Peer Reviewe
Unveiling the Impact of C60–O2 Interaction on the Performance and Characterization of Perovskite Solar Cells
No full textC60 is the prevalent electron‐transport layer (ETL) in high‐efficiency p‐i‐n perovskite single‐junction and multi‐junction solar cells. Here, it is demonstrated that the exposure of the C60 ETL to ambient O2 results in significantly increased non‐radiative recombination, influencing results from commonly applied characterization techniques such as steady‐state and transient photoluminescence (PL), transient surface photovoltage, as well as current density‐voltage measurements. Based on PL and He‐I UV photoemission spectroscopy measurements and supported by density functional theory calculations and drift‐diffusion simulations, it is proposed that O2 rapidly intercalates into the C60 ETL, causing the formation of deep trap states and an altered charge carrier balance at the perovskite/C60 interface. The findings reveal that the effect is reversible but can mislead experimental interpretations if disregarded, emphasizing the importance of O2 management during device fabrication and characterization. Furthermore, it is demonstrated that this interaction enables simple PL measurements in air to serve as a novel sensing method for evaluating the barrier layer quality of the SnOx buffer layer atop C60. This study thereby not only highlights a critical deterioration mechanism in perovskite solar cells and provides a deeper understanding of the underlying interaction between the C60 ETL and O2 but also offers practical avenues for future selective contact optimizations.“SHAPE” funded by the Federal Ministry of Economy and Climate Action (BMWK)“Supertandem” funded by the European Union's Horizon Europe research and innovation programPeer Reviewe
Semiconductor quantum dots as light sources in hybrid quantum networks
No full textQuantennetzwerke stellen die grundlegende Architektur zur Übertragung von Quantenzuständen dar. Photonen werden darin als Quanteninformationsträger im Freistrahl- oder Glasfaserkanal übersendet. Mögliche Lichtquellen und Quantenspeicher, wie zum Beispiel atomare Ensembles, Fehlstellen-Zentren in Diamant, epitaktische Quantenpunkte (QPe), Seltenerd-Ionen im Wirtskristall oder einzelne Ionen, bergen individuelle Vorteile und Herausforderungen.
Diese Arbeit verfolgt den Ansatz eines hybriden Quantennetzwerks aus verschiedenen Komponenten, die bestimmte Grundfunktionen optimal erfüllen. Epitaktische QPe haben sich als herausragende Quellen für einzelne und verschränkte Photonen erwiesen. Alkali-Atome können einzelne Photonen an ihren Übergängen im nahen Infrarot für Zeiten bis in den Sekundenbereich speichern und bieten Netzwerkknoten eine reproduzierbare Frequenzreferenz. Jedoch erfordert die Übertragung in Glasfasern bei geringen Verlusten eine Lichtwellenlänge im Telekommunikationsbereich von 1300 bis 1600 nm.
Das Ziel der Arbeit ist es, einen QP für den Einsatz in einem hybriden Netzwerk an ein Alkali-Atom-Ensemble anzubinden und mittels Frequenzumwandlung die Übertragung in Glasfaser zu ermöglichen. Dazu wurde die Emissionsfrequenz eines QPs auf den D1-Übergang von Cäsium-Atomen gestimmt und deren Wechselwirkung anhand der frequenzabhängigen Dispersion und Verzögerung durch Einzelphotonen-Spektroskopie und zeitkorrelierte Einzelphotonenzählung untersucht. Quantenfrequenzkonversion von QP-Einzel- und Paarphotonen wandelt ihre Wellenlänge von 894 nm des D1-Übergangs von Cäsium nach 1557 nm um. Darüber hinaus wurden erste Untersuchungen am ‚Lichtkäfig‘, einem neuartigen, durchlässigen Lichtleiter, im Hinblick auf die Anwendung als chipbasierten Quantenspeicher durchgeführt. Die erzielten Ergebnisse bilden die Grundlage für ein hybrides Quantennetzwerk aus QPen und Alkali-Atomen, die über Quantenfrequenzkonversion ihre Anbindung an Glasfasernetze finden.Quantum networks represent the foundational architecture for exchanging quantum states. Photons are transmitted through fiber-based or free-space channels as carriers of quantum information. Various sources of quantum light and platforms for quantum memory, such as atomic ensembles, defect centers in diamond, epitaxial quantum dots (QDs), rare-earth ions in host crystals, or single ions, entail individual advantages and challenges.
This thesis pursues the approach of a hybrid quantum network consisting of distinct components with optimal characteristics for their respective purpose. Epitaxial QDs have proven to be excellent sources of single and entangled pairs of photons. Alkali atoms may store a single photon for up to one second at transitions in the near infrared that present reproducible frequency references for each node of the network. However, the long-distance transmission of photons in fiber networks requires wavelengths in the telecommunication bands of 1300 to 1600 nm for minimal loss rates.
The goal of this work is to interface a QD with atoms of an alkali ensemble for their deployment in a hybrid quantum network and to facilitate the transfer in the fiber channel by frequency conversion. Therefore, the emission frequency of a single QD was tuned to the D1 transition of cesium atoms, and their interaction, in terms of the frequency-dependent dispersion and delay, was investigated by single-photon spectroscopy and time-correlated single-photon counting. The wavelength of QD single and pair photons was transformed from 894 nm of the D1 transition of cesium to 1557 nm by quantum frequency conversion. In addition, initial studies were carried out on the ‘light cage’, a novel permeable light-guiding structure, to assess its potential for chip-based quantum storage. The results lay the foundation for a hybrid quantum-network architecture built from QDs and alkali atoms that are connected through optical fibers via quantum frequency conversion
Quantum light detection in high-temperature superconducting nanowires
No full textDetection of light quanta in superconducting nano- and microwires is the key enabling technology for fields ranging from quantum optics and quantum photonics to emerging applications like dark matter searches. However, recent progress in accessing lower photon energies or utilizing high-temperature superconductors reveals substantial gaps in understanding quantum detection physics and calibrating photonic quantum systems. To bridge these gaps, we develop a universal model that incorporates spatially and energy-resolved detection physics, essential for photonic quantum sensors. We validate our approach using modern MgB2 nanowire detectors, retrieving their detection threshold and its intrinsic energy blur, by disentangling the complex statistics of single- and multi-photon detection. Our model can augment quantum detector tomography by embedding physical constraints, and it offers a practical tool for modeling and engineering a broad class of detectors under diverse operating conditions.Singapore’s Quantum Engineering Programmethe Swedish Research Council and the Swedish Space AgencyPeer Reviewe
Electromagnetic dynamic stability analysis of power electronics-dominated systems using eigenstructure-preserved LTP Theory
No full textSecure operation of power systems, one of the largest man-made systems, is crucial for economic development and societal well-being. Over the past century, initiatives like Europe’s Super Grid and China’s Dual Carbon plan have driven significant changes in power systems, leading to the widespread integration of diverse power electronic equipment. This has resulted in the emergence of power electronics-dominated power systems. However, they have experienced multiple electromagnetic oscillation accidents, causing large-scale renewable energy disconnections and even power equipment damage. To address these critical stability issues, now a global concern, the prevalent method relies on linear time-invariant approximate modeling, i.e., the eigenstructure-reconfiguration framework. While effective, it is limited by the curse of dimensionality in large-scale systems. Recently, the linear time-periodic theory has shown potential in accelerating calculations, but its analysis methods remain underdeveloped. In response to these challenges, we propose here a generalized linear time-periodic participation factor and sensitivity theory within the eigenstructure-preserved framework. This proposed participation factor significantly improves computational efficiency, outperforming eigenstructure-reconfiguration methods by orders of magnitude. Additionally, the proposed sensitivity analysis overcomes the lack of its analyticity. The potential of our methods is demonstrated through real-world power systems of China.National Outstanding Youth Foundation of Chinahttps://doi.org/10.13039/501100010225National Science Foundation of China | Young Scientists Fundhttps://doi.org/10.13039/501100010909National Science Foundation of China | Key Programmehttps://doi.org/10.13039/501100010903supported in part by Theme-based Research Scheme from the Research Grants Council, Hong Kong SAR under Grant T23-713/22-R, and in part by Collaborative Research Fund from the Research Grants Council, Hong Kong SAR under Grant C1052-21GFPeer Reviewe
Impact of Silicon Doping on High‐Temperature Annealed AlN/Sapphire Templates
No full textThe threading dislocation density (TDD) of epitaxially grown AlN layers on sapphire substrates can be significantly decreased by high‐temperature annealing (HTA). This study employs a process to improve the material quality of such AlN layers that comprises two AlN growth steps and two HTA steps. While the first AlN growth and subsequent annealing ensure an initial base TDD of 6 × 10 8 cm −2 for all samples, the subsequent AlN growth on these low TDD layers is varied in terms of silicon doping and layer thickness. Annealing of the doped and undoped samples reveals that both the silicon doping and an increase in AlN layer thickness lead to a further decrease in TDD down to 1.6 × 10 8 cm −2 without impairing the ultraviolet transparency. The impact of such improved AlN templates on the performance of ultraviolet‐C (UVC) light‐emitting diodes (LEDs) emitting around 234 nm is examined. It is found that a decrease in TDD from 4.9 × 10 8 cm −2 down to 2.9 × 10 8 cm −2 leads to an increase in optical power by a factor of 1.4. For AlN templates with even lower TDD, no further increase in optical power of the far‐UVC LEDs is observed, which can be related to dislocation half‐loop formation close to the active region.Bundesministerium für Bildung und Forschung 10.13039/501100002347Leibniz‐GemeinschaftPeer Reviewe
Fachspezifische Studien- und Prüfungsordnung für das lehramtsbezogene Masterstudium im Fach Französisch (Ein-Fach) (für das Lehramt an Integrierten Sekundarschulen und Gymnasien)
No full textStructural elucidation of the interaction of apicoplast resident ferredoxin and its interacting proteins
No full textPhD dissertation submitted for the award of PhD in BiochemistryDer Apicoplast ist ein essentielles, plastidenähnliches Organell, das aus der sekundären Endosymbiose roter Algen hervorgegangen ist und in den meisten Apicomplexa vorkommt. Er enthält mehrere für den Parasiten unverzichtbare Stoffwechselwege, die im Wirt fehlen, weshalb er ein geeignetes Ziel für neue Therapeutika gegen Malaria und Toxoplasmose darstellt. Ein zentrales System im Apicoplast ist das Ferredoxin‐Redoxsystem aus der Ferredoxin‐NADP⁺‐Reduktase pflanzlichen Typs (ptFNR) und ihrem Redoxpartner, dem Ferredoxin pflanzlichen Typs (ptFd), das Elektronen für verschiedene enzymatische Reaktionen bereitstellt. Die genauen Aminosäurereste an der Interaktionsschnittstelle zwischen ptFd und seinen Partnerenzymen waren jedoch bislang unbekannt. In dieser Studie wurde die Interaktionsoberfläche zwischen ptFd und dem IspH‐Enzym des MEP‐Wegs mithilfe eines E. coli‐Modells und computergestützter Methoden identifiziert, wodurch Herausforderungen bei der Analyse labiler Fe‐S‐Proteine überwunden wurden. Die Ergebnisse bestätigen die Bedeutung elektrostatischer Wechselwirkungen für die Erkennung zwischen den Proteinen und liefern wichtige Hinweise für die Entwicklung möglicher Hemmstoffe. Die Resultate des E. coli‐Modells konnten im Apicoplast von Toxoplasma gondii bestätigt werden, was dessen Eignung als erste Screening‐Plattform unterstreicht. Zudem zeigte eine Flavodoxin‐Komplementationsstudie evolutionäre Zusammenhänge zwischen Cyanobakterien, Chromera velia und Apicomplexa und deutet auf die Rolle von ptFd im SUF‐Weg der Fe‐S‐Biogenese hin. Insgesamt vertieft diese Arbeit das Verständnis der Funktion von ptFd als zentrale Elektronenverteilungsstelle in Apicomplexa.The apicoplast is an essential plastid-like organelle derived from red algae through secondary endosymbiosis and present in most Apicomplexa. It contains several metabolic pathways absent from the host and therefore represents a promising target for drugs against malaria and toxoplasmosis. A key system in the organelle is the ferredoxin redox system, composed of plant-type ferredoxin-NADP⁺ reductase (ptFNR) and plant-type ferredoxin (ptFd), which supplies electrons to multiple enzymes. Although protein-protein interaction is known to mediate electron transfer, the precise amino acid residues involved have remained unclear. In this study, the interaction interface between ptFd and the IspH enzyme of the MEP pathway was identified using an E. coli model combined with computational analysis, enabling the investigation of labile Fe-S proteins and protein complexes. The findings highlight the importance of electrostatic forces in the interaction and provide insights useful for inhibitor development. The E. coli results were reproduced in the apicoplast of Toxoplasma gondii, supporting the model as an efficient first screening system for functional mutations or drug effects before more demanding assays in parasites. Additional flavodoxin complementation experiments reveal evolutionary links between cyanobacteria, Chromera velia and Apicomplexa and suggest that the parasitic lifestyle may shape redox flexibility. The inability of flavodoxins to replace TgFd further indicates the involvement of ptFd in the SUF pathway for Fe-S biogenesis. Overall, this work advances understanding of the PfFd–PfIspH interface, the evolutionary context of ptFd and its role as a central electron hub in T. gondii and P. falciparum, reinforcing its relevance as a drug target
Toward understanding the scaling out of sustainable land use systems in Colombia: integrating case study insights and national pathways design for cacao farming
No full textThe unplanned expansion of conventional agriculture resulted in biodiversity loss and ecosystem degradation. Agroforestry systems (AFS) have emerged as a promising alternative to promote sustainable land use systems (SLUS) in tropical regions. This study explores the potential for scaling out SLUS from localized interventions to broader landscape-level applications in Colombian cacao agroforestry systems (CAFS). We employ a multi-level framework, integrating qualitative and quantitative data from primary and secondary sources. We apply text mining, cluster analysis, and principal component analysis. First, we identify the interconnections among agro-ecological, biophysical, economic, social, institutional, and political factors influencing the scaling out of SLUS in cacao farming in two municipalities located in conflict-affected Colombian departments. Secondly, we conduct a national quantitative exploratory analysis, grouping similar departments based on socioeconomic and biophysical data from official sources. This analysis provides the foundation for the design of regional typologies and an adaptive pathway for the scaling out of SLUS in cacao farming. This pathway encompasses five distinct departmental groups. Our findings highlight the need for a landscape-based approach that is sensitive to regional socio-cultural and institutional nuances. The analysis reveals that key variables, including land availability for agricultural use, water use risk level, deforestation, social conflict, land tenure informality, and agricultural productivity, influence the successful scaling out process across diverse regions. This study advocates for a collaborative approach that links scientific insights with practical initiatives co-created at the regional level, thereby empowering communities to design pathways for scaling out SLUS across Colombia.Open Access funding enabled and organized by Projekt DEAL.Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e.V. (3493)Peer Reviewe
Understanding Farmers' Policy Preferences for Solar‐Powered Irrigation Systems in Karnataka, India: A Choice Experiment Approach
No full textSolar‐Powered Irrigation Systems (SPIS) are an important component of India's effort towards sustainable energy transition and are promoted with financial support under the PM‐KUSUM program. In spite of the promise and the policy push, adoption of SPIS has been low. In this paper, we use a Discrete Choice Experiment (DCE) to evaluate the policy attributes in the promotion of SPIS. We selected five attributes of SPIS: cost of the pump; terms of the loan; grid connection; service provision (repair services); and multiple uses of energy (generated from solar panels) with different levels for each attribute. D‐efficient, non‐zero prior design was used to design the choice combinations used in the study. The data was collected from 500 farmers randomly chosen from 31 villages across Mysore district, Karnataka, India, and analysed using the random parameter logit model. For a nuanced interpretation and contextualisation of the results, we conducted follow‐up qualitative interviews. The results highlight that farmer preferences, indicated by the highest part worth, are for a loan with a longer repayment period (WTP of US 1498). Given that SPIS is a new technology with high initial investment, easing liquidity constraints and assuring farmers of guaranteed repair services are strong incentives to adopt it. These findings can be incorporated into existing policies so that they align well with farmers' preferences.Indian Council of Agricultural Research 10.13039/501100001503Peer Reviewe