160 results on '"Markus Döblinger"'
Search Results
2. Building Blocks and COFs Formed in Concert – Three Component Synthesis of Pyrene‐Fused Azaacene Covalent Organic Framework in the Bulk and as Films
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Laura Frey, Orlando Oliveira, Ashish Sharma, Roman Guntermann, Soraia P. S. Fernandes, Krystal M. Cid-Seara, Hosanna Abbay, Herny Thornes, Joao Rocha, Markus Döblinger, Tim Kowalczyk, Akshay Rao, Laura M. Salonen, and Dana D. Medina
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General Chemistry ,General Medicine ,Catalysis - Published
- 2023
3. Heterogeneous III-V nanowire quantum emitters on silicon photonic circuits
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Hyowon Jeong, Akhil Ajay, Nitin Mukhundhan, Markus Döblinger, Jonathan J. Finley, and Gregor Koblmüller
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- 2023
4. Sb‐Mediated Tuning of Growth‐ and Exciton Dynamics in Entirely Catalyst‐Free GaAsSb Nanowires
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Hyowon W. Jeong, Akhil Ajay, Haiting Yu, Markus Döblinger, Nitin Mukhundhan, Jonathan J. Finley, and Gregor Koblmüller
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Biomaterials ,General Materials Science ,General Chemistry ,Biotechnology - Published
- 2023
5. 1,10-Phenanthroline as an Efficient Bifunctional Passivating Agent for MAPbI3 Perovskite Solar Cells
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Peter Müller-Buschbaum, Marcella Günther, Ali Buyruk, Markus Döblinger, Andreas Weis, Dominic Blätte, Manuel A. Scheel, Nicolai F. Hartmann, Tayebeh Ameri, Thomas Bein, and Achim Hartschuh
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Photocurrent ,1,10-phenanthroline ,Materials science ,multiple ligands ,Passivation ,computer.internet_protocol ,lead iodide ,perovskite solar cells ,defects passivation ,FTPS ,Light intensity ,Chemical engineering ,Scanning transmission electron microscopy ,General Materials Science ,Grain boundary ,Thin film ,computer ,Perovskite (structure) - Abstract
Passivation is one of the most promising concepts to heal defects created at the surface and grain boundaries of polycrystalline perovskite thin films, which significantly deteriorate the photovoltaic performance and stability of corresponding devices. Here, 1,10-phenanthroline, known as a bidentate chelating ligand, is implemented between the methylammonium lead iodide (MAPbI3) film and the hole-transport layer for both passivating the lead-based surface defects (undercoordinated lead ions) and converting the excess/unreacted lead iodide (PbI2) buried at interfaces, which is problematic for the long-term stability, into "neutralized"and beneficial species (PbI2(1,10-phen)x, x = 1, 2) for efficient hole transfer at the modified interface. The defect healing ability of 1,10-phenanthroline is verified with a set of complementary techniques including photoluminescence (steady-state and time-resolved), space-charge-limited current (SCLC) measurements, light intensity dependent JV measurements, and Fourier-transform photocurrent spectroscopy (FTPS). In addition to these analytical methods, we employ advanced X-ray scattering techniques, nano-Fourier transform infrared (nano-FTIR) spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to further analyze the structure and chemical composition at the perovskite surface after treatment at nanoscale spatial resolution. On the basis of our experimental results, we conclude that 1,10-phenanthroline treatment induces the formation of different morphologies with distinct chemical compositions on the surface of the perovskite film such that surface defects are effectively passivated, and excess/unreacted PbI2 is converted into beneficial complex species at the modified interface. As a result, an improved power conversion efficiency (20.16%) and significantly more stable unencapsulated perovskite solar cells are obtained with the 1,10-phenanthroline treatment compared to the MAPbI3 reference device (18.03%).
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- 2021
6. An Electrically Conducting Three‐Dimensional Iron–Catecholate Porous Framework
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Timothy Clark, Julian M. Rotter, Pouya Hosseini, Patricia I. Scheurle, Markus Döblinger, Irina Santourian, Gunther Wittstock, Thomas Bein, Dominik Fehn, Karsten Meyer, Matthias Hennemann, Alfred Schirmacher, Dana D. Medina, Andre Mähringer, and Christoph Gruber
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porosity ,Materials science ,electrical conductivity ,three-dimensional framework ,Sorption ,General Chemistry ,Electron ,General Medicine ,Catalysis ,Ion ,metal–organic frameworks ,Chemical engineering ,Electrical resistivity and conductivity ,ddc:540 ,Metal–Organic Frameworks | Hot Paper ,Metal-organic framework ,Crystallite ,iron-catecholate ,Absorption (chemistry) ,Porosity ,Research Articles ,Research Article - Abstract
We report the synthesis of a unique cubic metal–organic framework (MOF), Fe‐HHTP‐MOF, comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions, arranged in a diamond topology. The MOF is synthesized under solvothermal conditions, yielding a highly crystalline, deep black powder, with crystallites of 300–500 nm size and tetrahedral morphology. Nitrogen sorption analysis indicates a highly porous material with a surface area exceeding 1400 m2 g−1. Furthermore, Fe‐HHTP‐MOF shows broadband absorption from 475 up to 1900 nm with excellent absorption capability of 98.5 % of the incoming light over the visible spectral region. Electrical conductivity measurements of pressed pellets reveal a high intrinsic electrical conductivity of up to 10−3 S cm−1. Quantum mechanical calculations predict Fe‐HHTP‐MOF to be an efficient electron conductor, exhibiting continuous charge‐carrier pathways throughout the structure., Fe‐HHTP‐MOF, a unique cubic metal–organic framework (MOF) comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions arranged in a diamond topology is reported. Fe‐HHTP‐MOF is a highly crystalline, porous and deep black material featuring high electrical conductivity.
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- 2021
7. Epitaxial type-I and type-II InAs-AlAsSb core–shell nanowires on silicon
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Steffen Meder, Paul Schmiedeke, Fabio del Giudice, Markus Döblinger, Gregor Koblmüller, Sergej Fust, H. Riedl, Johannes Pantle, Jonathan J. Finley, and Akhil Ajay
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010302 applied physics ,Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,Nanowire ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,7. Clean energy ,01 natural sciences ,Band offset ,ddc ,symbols.namesake ,Semiconductor ,chemistry ,0103 physical sciences ,symbols ,Optoelectronics ,Photonics ,0210 nano-technology ,business ,Spectroscopy ,Raman scattering - Abstract
Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core–shell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs–AlAsSb core–shell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III–V materials family. We develop direct monolithic growth of high-uniformity InAs–AlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.
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- 2022
8. Interfacial Manganese‐Doping in CsPbBr 3 Nanoplatelets by Employing a Molecular Shuttle
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Linzhong Wu, Yiou Wang, Mariam Kurashvili, Amrita Dey, Muhan Cao, Markus Döblinger, Qiao Zhang, Jochen Feldmann, He Huang, and Tushar Debnath
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General Medicine ,General Chemistry ,Catalysis - Published
- 2022
9. Growth of Perovskite CsPbBr3 Nanocrystals and Their Formed Superstructures Revealed by In Situ Spectroscopy
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He Huang, Alexander F. Richter, Bert Nickel, Maximilian W. Feil, Yiou Wang, Tushar Debnath, Linzhong Wu, Markus Döblinger, Simon Fuchs, and Yu Tong
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Materials science ,Field (physics) ,General Chemical Engineering ,Halide ,Nanotechnology ,02 engineering and technology ,General Chemistry ,In situ spectroscopy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Metal ,Nanocrystal ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,0210 nano-technology ,Perovskite (structure) - Abstract
Metal halide perovskites have attracted substantial interest because of their promising properties for optoelectronic applications. Despite much progress made in the field, the exact growth mechani...
- Published
- 2020
10. Template‐basierte Herstellung von 2D‐photonischen Superkristallen mit verstärkter spontaner Emission aus CsPbBr 3 ‐Perowskit‐Nanokristallen
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Agustín Mihi, He Huang, Aurora Manzi, Lakshminarayana Polavarapu, Maximilian W. Feil, Jochen Feldmann, David Vila-Liarte, Markus Döblinger, Juan Luis Garcia-Pomar, and Luis M. Liz-Marzán
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02 engineering and technology ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Published
- 2020
11. Mangan‐Dotierung von Perowskit‐Nanokristallen: Quanteneinschränkung Aufgrund von Ruddlesden‐Popper‐Defekten
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Lakshminarayana Polavarapu, Alexander F. Richter, Markus Döblinger, Yu Tong, Amrita Dey, Tushar Debnath, Sara Bals, Eva Bladt, He Huang, Jochen Feldmann, and Sharmistha Paul
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Materials science ,02 engineering and technology ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Published
- 2020
12. Nanocellulose‐Mediated Transition of Lithium‐Rich Pseudo‐Quaternary Metal Oxide Nanoparticles into Lithium Nickel Cobalt Manganese Oxide (NCM) Nanostructures
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Michael Beetz, Bernhard Böller, Sebastian Häringer, Maximilian A. Plaß, Florian Zoller, Markus Döblinger, Peter M. Zehetmaier, Dina Fattakhova-Rohlfing, and Thomas Bein
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Materials science ,Nanostructure ,Renewable Energy, Sustainability and the Environment ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Nanoparticle ,Metal oxide nanoparticles ,Manganese oxide ,Nanocellulose ,Biomaterials ,Nickel ,chemistry ,Chemical engineering ,ddc:540 ,Materials Chemistry ,Lithium ,Cobalt ,Elektrotechnik - Abstract
We report the syntheses of various compounds within the pseudo-quaternary system of the type LiwNiₓCoyMnzOδ (δ≤1) (pre-NCMs). Four different compositions of this compound were realized as ultrasmall crystalline nanoparticles of 1–4 nm diameter using low-temperature solvothermal reaction conditions in tert-butanol at only 170 °C. All of the pre-NCMs crystallize in the rock-salt structure and their lithium content is between 20% and 30% with respect to the complete metal content. By adjusting the lithium content to 105% stoichiometry in the solvothermal reaction, the pre-NCMs can easily react to the respective Li(NiₓCoyMnz)O₂ (NCM) nanoparticles. Furthermore, nanosized desert-rose structured NCMs were obtained after addition of nanocellulose during the synthesis. By using the mixed metal monoxides as precursor for the NCMs, cation mixing between lithium and nickel is favored and gets more pronounced with increasing nickel content. The cation mixing effect compromises good electrochemical capacity retention, but the desert-rose structure nevertheless enables enhanced stability at high power conditions, especially for NCM333.
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- 2020
13. Nonvolatile Memristive Switching in Self-assembled Nanoparticle Dimers
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Marc Tornow, Maximilian Speckbacher, Matthias Jakob, Ueli Heiz, Markus Döblinger, Aras Kartouzian, and Jonathan G. C. Veinot
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Materials science ,Agglomerate ,Materials Chemistry ,Electrochemistry ,Nanoparticle ,Nanotechnology ,Self-assembly ,Suspension (vehicle) ,Electronic, Optical and Magnetic Materials ,Self assembled - Abstract
The selective formation of heterogeneous nanoparticle (NP) agglomerates and their memristive switching properties are reported. Following surfactant-mediated self-assembly in suspension, agglomerat...
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- 2020
14. Manganese‐Doping‐Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden–Popper Defects
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Tushar Debnath, Markus Döblinger, He Huang, Lakshminarayana Polavarapu, Amrita Dey, Sharmistha Paul, Yu Tong, Sara Bals, Alexander F. Richter, Eva Bladt, and Jochen Feldmann
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Materials science ,Energy transfer ,CsPbX3 nanocrystals ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,quantum confinement ,Catalysis ,Ion ,exciton properties ,Photoluminescence ,Manganese doping ,manganese-doped perovskite nanocrystals ,Dopant ,010405 organic chemistry ,Communication ,Doping ,Ruddlesden–Popper defects ,General Chemistry ,Communications ,0104 chemical sciences ,3. Good health ,Blueshift ,Chemistry ,Nanocrystal ,Chemical physics ,Quantum dot - Abstract
The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively., The doping of Mn2+ ions into CsPbCl3 nanocrystals (NCs) strongly influences the excitonic properties of the host NCs. Manganese doping leads to the formation of Ruddlesden–Popper defects and thus induces quantum confinement within individual crystals. This results in a blue shift of the excitonic emission.
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- 2020
15. Porphyrinic Mof Derived Single-Atom Electrocatalyst Enables Methanol Oxidation
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Zhenyu Zhou, Jing Zhang, Soumya Mukherjee, Shujin Hou, Rachit Khare, Markus Döblinger, Ondřej Tomanec, Michal Otyepka, Max Koch, Liujiang Zhou, Weijin Li, and Roland A. Fischer
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History ,Polymers and Plastics ,Business and International Management ,Industrial and Manufacturing Engineering - Published
- 2022
16. Interfacial Manganese-Doping in CsPbBr
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Linzhong, Wu, Yiou, Wang, Mariam, Kurashvili, Amrita, Dey, Muhan, Cao, Markus, Döblinger, Qiao, Zhang, Jochen, Feldmann, He, Huang, and Tushar, Debnath
- Abstract
Mn-doping in cesium lead halide perovskite nanoplatelets (NPls) is of particular importance where strong quantum confinement plays a significant role towards the exciton-dopant coupling. In this work, we report an immiscible bi-phasic strategy for post-synthetic Mn-doping of CsPbX
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- 2021
17. Porphyrinic MOF derived Single-atom electrocatalyst enables methanol oxidation
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Zhenyu Zhou, Jing Zhang, Soumya Mukherjee, Shujin Hou, Rachit Khare, Markus Döblinger, Ondřej Tomanec, Michal Otyepka, Max Koch, Pan Gao, Liujiang Zhou, Weijin Li, and Roland A. Fischer
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General Chemical Engineering ,Environmental Chemistry ,General Chemistry ,Industrial and Manufacturing Engineering - Published
- 2022
18. Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy
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Daniel Ruhstorfer, Markus Döblinger, Hubert Riedl, Jonathan J. Finley, and Gregor Koblmüller
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General Physics and Astronomy - Abstract
We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.
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- 2022
19. Dark and Bright Excitons in Halide Perovskite Nanoplatelets
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Moritz Gramlich, Michael W. Swift, Carola Lampe, John L. Lyons, Markus Döblinger, Alexander L. Efros, Peter C. Sercel, and Alexander S. Urban
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Condensed Matter - Materials Science ,optoelectronics ,Science ,General Chemical Engineering ,nanoplatelets ,General Engineering ,General Physics and Astronomy ,Medicine (miscellaneous) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,exciton fine structure ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry, Genetics and Molecular Biology (miscellaneous) ,effective mass model ,0104 chemical sciences ,Condensed Matter::Materials Science ,photoluminescence spectroscopy ,halide perovskites ,General Materials Science ,0210 nano-technology - Abstract
Semiconductor nanoplatelets (NPLs), with their large exciton binding energy, narrow photoluminescence (PL), and absence of dielectric screening for photons emitted normal to the NPL surface, could be expected to become the fastest luminophores amongst all colloidal nanostructures. However, super‐fast emission is suppressed by a dark (optically passive) exciton ground state, substantially split from a higher‐lying bright (optically active) state. Here, the exciton fine structure in 2–8 monolayer (ML) thick Csn − 1PbnBr3n + 1 NPLs is revealed by merging temperature‐resolved PL spectra and time‐resolved PL decay with an effective mass model taking quantum confinement and dielectric confinement anisotropy into account. This approach exposes a thickness‐dependent bright–dark exciton splitting reaching 32.3 meV for the 2 ML NPLs. The model also reveals a 5–16 meV splitting of the bright exciton states with transition dipoles polarized parallel and perpendicular to the NPL surfaces, the order of which is reversed for the thinnest NPLs, as confirmed by TR‐PL measurements. Accordingly, the individual bright states must be taken into account, while the dark exciton state strongly affects the optical properties of the thinnest NPLs even at room temperature. Significantly, the derived model can be generalized for any isotropically or anisotropically confined nanostructure.
- Published
- 2021
20. 1,10-Phenanthroline as an Efficient Bifunctional Passivating Agent for MAPbI
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Ali, Buyruk, Dominic, Blätte, Marcella, Günther, Manuel A, Scheel, Nicolai F, Hartmann, Markus, Döblinger, Andreas, Weis, Achim, Hartschuh, Peter, Müller-Buschbaum, Thomas, Bein, and Tayebeh, Ameri
- Abstract
Passivation is one of the most promising concepts to heal defects created at the surface and grain boundaries of polycrystalline perovskite thin films, which significantly deteriorate the photovoltaic performance and stability of corresponding devices. Here, 1,10-phenanthroline, known as a bidentate chelating ligand, is implemented between the methylammonium lead iodide (MAPbI
- Published
- 2021
21. Spontane Kristallisation von Perowskit‐Nanokristallen in unpolaren organischen Lösungsmitteln: Ein vielseitiges Konzept für deren morphologiekontrollierende Synthese
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He Huang, Yu Tong, Lakshminarayana Polavarapu, Yanxiu Li, En-Ping Yao, Maximilian W. Feil, Jochen Feldmann, Alexander F. Richter, Andrey L. Rogach, and Markus Döblinger
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Materials science ,010405 organic chemistry ,General Medicine ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences - Published
- 2019
22. Breakdown of Corner States and Carrier Localization by Monolayer Fluctuations in Radial Nanowire Quantum Wells
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Anna Sitek, Gerhard Abstreiter, Hubert J. Krenner, Daniel Ruhstorfer, Markus Döblinger, D. Rudolph, Lisa Janker, Maximilian M. Sonner, Jonathan J. Finley, Gregor Koblmüller, Andrei Manolescu, and Achim Wixforth
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3D optical data storage ,Materials science ,Mechanical Engineering ,Surface acoustic wave ,Nanowire ,Bioengineering ,Heterojunction ,02 engineering and technology ,General Chemistry ,Electron ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Molecular physics ,Monolayer ,ddc:530 ,General Materials Science ,Charge carrier ,0210 nano-technology ,Quantum well - Abstract
We report a comprehensive study of the impact of the structural properties in radial GaAs-Al0.3Ga0.7As nanowire-quantum well heterostructures on the optical recombination dynamics and electrical transport properties, emphasizing particularly the role of the commonly observed variations of the quantum well thickness at different facets. Typical thickness fluctuations of the radial quantum well observed by transmission electron microscopy lead to pronounced localization. Our optical data exhibit clear spectral shifts and a multipeak structure of the emission for such asymmetric ring structures resulting from spatially separated, yet interconnected quantum well systems. Charge carrier dynamics induced by a surface acoustic wave are resolved and prove efficient carrier exchange on native, subnanosecond time scales within the heterostructure. Experimental findings are corroborated by theoretical modeling, which unambiguously show that electrons and holes localize on facets where the quantum well is the thickes...
- Published
- 2019
23. DNA‐Origami‐Templated Silica Growth by Sol–Gel Chemistry
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Tim Liedl, Linh Nguyen, Markus Döblinger, and Amelie Heuer-Jungemann
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Lattice deformation ,Materials science ,010405 organic chemistry ,Structural integrity ,Nanotechnology ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Sol gel chemistry ,DNA nanotechnology ,DNA origami ,Silica coating - Abstract
Improving the stability of DNA origami structures with respect to thermal, chemical, and mechanical demands will be essential to fully explore the real-life applicability of DNA nanotechnology. Here we present a strategy to increase the mechanical resilience of individual DNA origami objects and 3D DNA origami crystals in solution as well as in the dry state. By encapsulating DNA origami in a protective silica shell using sol-gel chemistry, all the objects maintain their structural integrity. This allowed for a detailed structural analysis of the crystals in a dry state, thereby revealing their true 3D shape without lattice deformation and drying-induced collapse. Analysis by energy-dispersive X-ray spectroscopy showed a uniform silica coating whose thickness could be controlled through the precursor concentrations and reaction time. This strategy thus facilitates shape-controlled bottom-up synthesis of designable biomimetic silica structures through transcription from DNA origami.
- Published
- 2019
24. Tailoring Plasmonic Bimetallic Nanocatalysts Toward Sunlight‐Driven H 2 Production
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Matias Herran, Ana Sousa‐Castillo, Chenghao Fan, Seunghoon Lee, Wei Xie, Markus Döblinger, Baptiste Auguié, and Emiliano Cortés
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Biomaterials ,Electrochemistry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2022
25. Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties
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L. Suomenniemi, J. Treu, Daniel Ruhstorfer, Markus Döblinger, J. Becker, F. del Giudice, C. de Rose, Jonathan J. Finley, Gregor Koblmüller, and H. Riedl
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010302 applied physics ,Materials science ,Silicon ,business.industry ,Annealing (metallurgy) ,Transistor ,Degenerate energy levels ,Nanowire ,Conductance ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,law.invention ,Catalysis ,chemistry ,law ,0103 physical sciences ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor–solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
- Published
- 2020
26. Growth and Formation of Perovskite Nanocrystals and Their Superstructures Revealed by In-situ Spectroscopy
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He Huang, Maximilian W. Feil, Simon Fuchs, Tushar Debnath, Alexander F. Richter, Yu Tong, Linzhong Wu, Yiou Wang, Markus Döblinger, and Bert Nickel
- Subjects
perovskite - Abstract
Metal halide perovskites have attracted substantial interest because of their promising properties for optoelectronic applications. Despite much progress made in the field, the exact growth mechanism of perovskite nanocrystals (e.g., CsPbBr3) remains elusive and further improvement of their controllable synthesis is challenging. Herein, we point out different phenomena during the processes of growth, cooling, and purification of high-quality CsPbBr3 nanocrystals using in situ photoluminescence spectroscopy. The as-synthesized materials have been further characterized by timeresolved transient differential transmission and photoluminescence spectroscopies. Using X-ray scattering, we confirm that nanocrystals form superstructures during the process of cooling already in dispersion, which is frequently ignored. The purification process is explained using a proposed model based on the self-size-selection. On the one hand, such superstructures pave a potential pathway to the fabrication of highquality devices such as light-emitting devices. On the other hand, the approach to reveal their formation process benefits the comparison and understanding of the difference between nanocrystals and supercrystals. The fact that superstructures form already during synthesis may also apply to the different perovskite systems and thus help to improve the quality of the as-prepared nanocrystals.
- Published
- 2020
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27. Excitons and narrow bands determine the optical properties of cesium bismuth halides
- Author
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Alexander F. Richter, Jacek K. Stolarczyk, Peter Müller-Buschbaum, Linn Leppert, Jochen Feldmann, Markus Döblinger, Lakshminarayana Polavarapu, Yu Tong, Kun Wang, Bernhard J. Bohn, and Sebastian Rieger
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Physics ,Photoluminescence ,Absorption spectroscopy ,Band gap ,Binding energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Reciprocal lattice ,0103 physical sciences ,Direct and indirect band gaps ,Density functional theory ,Atomic physics ,010306 general physics ,0210 nano-technology ,Bohr radius - Abstract
We study the optical properties of ${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{I}}_{9}$ nanoplatelets using a combination of first-principles density functional theory, $\mathit{GW}$ plus Bethe-Salpeter equation calculations, and spectroscopic experiments. We show that the material exhibits flat bands and hence high effective masses. This manifests itself in the lowest-energy transition in the absorption spectrum arising from excitons with a high binding energy of 300 meV and a Bohr radius smaller than 6 nm. Due to the indirect band gap, electrons and holes are efficiently separated in reciprocal space and recombine slowly across the band gap, leading to very weak photoluminescence. Our results resolve inconsistencies in previous studies on ${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{I}}_{9}$ and lay the groundwork for further applications of this material, reliant on charge separation.
- Published
- 2019
28. Connecting Composition-Driven Faceting with Facet-Driven Composition Modulation in GaAs–AlGaAs Core–Shell Nanowires
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Gregor Koblmüller, Daniel Ruhstorfer, Markus Döblinger, Lincoln J. Lauhon, Bernhard Loitsch, Sonja Matich, and Nari Jeon
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Materials science ,business.industry ,Band gap ,Mechanical Engineering ,Nanowire ,Bioengineering ,Heterojunction ,Context (language use) ,02 engineering and technology ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Faceting ,Condensed Matter::Materials Science ,0103 physical sciences ,Scanning transmission electron microscopy ,Optoelectronics ,General Materials Science ,Facet ,010306 general physics ,0210 nano-technology ,business ,Quantum well - Abstract
Ternary III-V alloys of tunable bandgap are a foundation for engineering advanced optoelectronic devices based on quantum-confined structures including quantum wells, nanowires, and dots. In this context, core-shell nanowires provide useful geometric degrees of freedom in heterostructure design, but alloy segregation is frequently observed in epitaxial shells even in the absence of interface strain. High-resolution scanning transmission electron microscopy and laser-assisted atom probe tomography were used to investigate the driving forces of segregation in nonplanar GaAs-AlGaAs core-shell nanowires. Growth-temperature-dependent studies of Al-rich regions growing on radial {112} nanofacets suggest that facet-dependent bonding preferences drive the enrichment, rather than kinetically limited diffusion. Observations of the distinct interface faceting when pure AlAs is grown on GaAs confirm the preferential bonding of Al on {112} facets over {110} facets, explaining the decomposition behavior. Furthermore, three-dimensional composition profiles generated by atom probe tomography reveal the presence of Al-rich nanorings perpendicular to the growth direction; correlated electron microscopy shows that short zincblende insertions in a nanowire segment with predominantly wurtzite structure are enriched in Al, demonstrating that crystal phase engineering can be used to modulate composition. The findings suggest strategies to limit alloy decomposition and promote new geometries of quantum confined structures.
- Published
- 2018
29. Correlated Chemical and Electrically Active Dopant Analysis in Catalyst-Free Si-Doped InAs Nanowires
- Author
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J. Treu, Lincoln J. Lauhon, Markus Döblinger, H. Riedl, Max Sonner, Alexander Hirler, Megan O. Hill, J. Becker, Gregor Koblmüller, and Jonathan J. Finley
- Subjects
010302 applied physics ,Materials science ,Dopant ,business.industry ,Doping ,General Engineering ,Nanowire ,General Physics and Astronomy ,02 engineering and technology ,Atom probe ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,Semiconductor ,law ,0103 physical sciences ,Thermoelectric effect ,Electrode ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Molecular beam epitaxy - Abstract
Direct correlations between dopant incorporation, distribution, and their electrical activity in semiconductor nanowires (NW) are difficult to access and require a combination of advanced nanometrology methods. Here, we present a comprehensive investigation of the chemical and electrically active dopant concentrations in n-type Si-doped InAs NW grown by catalyst-free molecular beam epitaxy using various complementary techniques. N-type carrier concentrations are determined by Seebeck effect measurements and four-terminal NW field-effect transistor characterization and compared with the Si dopant distribution analyzed by local electrode atom probe tomography. With increased dopant supply, a distinct saturation of the free carrier concentration is observed in the mid-1018 cm-3 range. This behavior coincides with the incorporated Si dopant concentrations in the bulk part of the NW, suggesting the absence of compensation effects. Importantly, excess Si dopants with very high concentrations (>1020 cm-3) segregate at the NW sidewall surfaces, which confirms recent first-principles calculations and results in modifications of the surface electronic properties that are sensitively probed by field-effect measurements. These findings are expected to be relevant also for doping studies of other noncatalytic III-V NW systems.
- Published
- 2018
30. Highly stable and porous porphyrin-based zirconium and hafnium phosphonates – electron crystallography as an important tool for structure elucidation
- Author
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Markus Döblinger, Haishuang Zhao, Helge Reinsch, Timo Rhauderwiek, Bart Bueken, Dirk De Vos, Patrick Hirschle, Norbert Stock, Ute Kolb, and Stefan Wuttke
- Subjects
PORES ,Materials science ,Chemistry, Multidisciplinary ,chemistry.chemical_element ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,01 natural sciences ,AQUEOUS-SOLUTION ,METAL-ORGANIC FRAMEWORKS ,chemistry.chemical_compound ,DESIGN ,AUTOMATED DIFFRACTION TOMOGRAPHY ,Formula unit ,Molecule ,CRYSTAL-STRUCTURE ,Zirconium ,Science & Technology ,STABILITY ,General Chemistry ,021001 nanoscience & nanotechnology ,Porphyrin ,0104 chemical sciences ,Chemistry ,MANGANESE PORPHYRINS ,Crystallography ,chemistry ,Electron diffraction ,Physical Sciences ,LIGANDS ,Chemical stability ,Cyclic voltammetry ,0210 nano-technology ,SYSTEM - Abstract
The Ni-metallated porphyrin-based tetraphosphonic acid (Ni-tetra(4-phosphonophenyl)porphyrin, Ni-H8TPPP) was used for the synthesis of highly porous metal phosphonates containing the tetravalent cations Zr4+ and Hf4+. The compounds were thoroughly characterized regarding their sorption properties towards N2 and H2O as well as thermal and chemical stability. During the synthesis optimization the reaction time could be substantially decreased under stirring from 24 to 3 h in glass vials. M-CAU-30, [M2(Ni-H2TPPP)(OH/F)2]·H2O (M = Zr, Hf) shows exceptionally high specific surface areas for metal phosphonates of aBET = 1070 and 1030 m2 g-1 for Zr- and Hf-CAU-30, respectively, which are very close/correspond to the theoretical values of 1180 and 1030 m2 g-1. CAU-30 is always obtained as mixtures with one mol ZrO2/HfO2 per formula unit as proven by TEM, electron diffraction, TG and elemental analysis. Hence experimentally derived specific surface areas are 970 and 910 m2 g-1, respectively. M-CAU-30 is chemically stable in the pH range 0 to 12 in HCl/NaOH and thermally up to 420 °C in air as determined by variable-temperature powder X-ray diffraction (VT-PXRD). The crystal structure of M-CAU-30 was determined by combining electron diffraction tomography for structure solution and powder X-ray diffraction data for the structure refinement. The crystal structure consists of chains of corner sharing MO6 octahedra interconnected by the partly deprotonated linker molecules Ni-H2TPPP6-. Thus 1D channels with pore diameters of 1.3 × 2.0 nm are formed. The redox activity of Zr-CAU-30 was investigated by cyclic voltammetry resulting in a reversible redox process at a half-wave potential of E1/2 = -0.649 V. ispartof: CHEMICAL SCIENCE vol:9 issue:24 pages:5467-5478 ispartof: location:England status: published
- Published
- 2018
31. Oriented Films of Conjugated 2D Covalent Organic Frameworks as Photocathodes for Water Splitting
- Author
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Alexander G. Hufnagel, Markus Döblinger, Austin M. Evans, Kristina Peters, Ilina Kondofersky, Julian M. Rotter, Paul Knochel, Daniel Böhm, Dina Fattakhova-Rohlfing, Dana D. Medina, Simon Herbert, Jonathan Kampmann, Thomas Bein, Torben Sick, and Mona Calik
- Subjects
Hydrogen ,Stacking ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Electrolyte ,Conjugated system ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,Biochemistry ,Article ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Elektrotechnik ,Electrolysis of water ,Chemistry ,business.industry ,General Chemistry ,Tetraphenylethylene ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Semiconductor ,Water splitting ,0210 nano-technology ,business - Abstract
Light-driven water electrolysis at a semiconductor surface is a promising way to generate hydrogen from sustainable energy sources, but its efficiency is limited by the performance of available photoabsorbers. Here we report the first time investigation of covalent organic frameworks (COFs) as a new class of photoelectrodes. The presented 2D-COF structure is assembled from aromatic amine-functionalized tetraphenylethylene and thiophene-based dialdehyde building blocks to form conjugated polyimine sheets, which π-stack in the third dimension to create photoactive porous frameworks. Highly oriented COF films absorb light in the visible range to generate photoexcited electrons that diffuse to the surface and are transferred to the electrolyte, resulting in proton reduction and hydrogen evolution. The observed photoelectrochemical activity of the 2D-COF films and their photocorrosion stability in water pave the way for a novel class of photoabsorber materials with versatile optical and electronic properties that are tunable through the selection of appropriate building blocks and their three-dimensional stacking.
- Published
- 2017
32. Titelbild: An Electrically Conducting Three‐Dimensional Iron–Catecholate Porous Framework (Angew. Chem. 33/2021)
- Author
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Irina Santourian, Patricia I. Scheurle, Christoph Gruber, Markus Döblinger, Alfred Schirmacher, Gunther Wittstock, Dominik Fehn, Thomas Bein, Julian M. Rotter, Dana D. Medina, Pouya Hosseini, Andre Mähringer, Karsten Meyer, Matthias Hennemann, and Timothy Clark
- Subjects
Materials science ,Chemical engineering ,Electrical resistivity and conductivity ,Metal-organic framework ,General Medicine ,Porosity - Published
- 2021
33. Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature
- Author
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Andreas Thurn, Gregor Koblmüller, Paul Schmiedeke, Jonathan J. Finley, Sonja Matich, and Markus Döblinger
- Subjects
010302 applied physics ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Band gap ,Relaxation (NMR) ,Nanowire ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,Core (optical fiber) ,law ,0103 physical sciences ,Optoelectronics ,Coaxial ,0210 nano-technology ,business ,Lasing threshold ,Quantum well - Abstract
Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.
- Published
- 2021
34. Nonagglomerated Iron Oxyhydroxide Akaganeite Nanocrystals Incorporating Extraordinary High Amounts of Different Dopants
- Author
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Markus Döblinger, Siyuan Zhang, Alena Folger, Thomas Bein, Daniel Böhm, Dina Fattakhova-Rohlfing, Ksenia Fominykh, and Christina Scheu
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Materials science ,Dopant ,Akaganéite ,General Chemical Engineering ,Doping ,Solvothermal synthesis ,Chemie ,Mineralogy ,02 engineering and technology ,General Chemistry ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Crystal ,Chemical engineering ,Materials Chemistry ,engineering ,Particle ,Nanorod ,Thin film ,0210 nano-technology - Abstract
Dispersible nonagglomerated akaganeite (β-FeOOH) nanocrystals doped with various elements in different oxidation states such as Co(II), Ni(II), V(III), Ti(IV), Sn(IV), Si(IV), and Nb(V) were prepared using a microwave-assisted solvothermal synthesis in tert-butanol. The doping elements could be incorporated in very high concentrations of up to 20 at. %, which is attributed to the kinetic control of the phase formation during the solvothermal reaction, together with the extremely small crystal size, which can stabilize the unusual structural compositions. The particle morphology is mostly anisotropic consisting of nanorods ∼4 nm in width and varying length. Depending on the doping element, the length ranges from ∼4 nm, resulting in an almost-spherical shape, to 90 nm, giving the highest aspect ratio. The particles are perfectly dispersible in water, giving stable colloidal dispersions that can be deposited on different substrates to produce thin films 35–250 nm thick. In addition, films up to 30 μm thick, ...
- Published
- 2017
35. Quantum Transport and Sub-Band Structure of Modulation-Doped GaAs/AlAs Core–Superlattice Nanowires
- Author
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Bernhard Loitsch, Gerhard Abstreiter, Jonathan J. Finley, Stefanie Morkötter, J. Becker, Jakob Seidl, Dominik M. Irber, Yang Tang, Lincoln J. Lauhon, Damon J. Carrad, Matthew Grayson, Sonja Matich, Markus Döblinger, Gregor Koblmüller, Nari Jeon, and Julia Winnerl
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,business.industry ,Mechanical Engineering ,Superlattice ,Nanowire ,Bioengineering ,Heterojunction ,02 engineering and technology ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Condensed Matter::Materials Science ,Semiconductor ,Atomic orbital ,Quantum dot ,0103 physical sciences ,Scanning transmission electron microscopy ,General Materials Science ,0210 nano-technology ,business ,Electronic band structure - Abstract
Modulation-doped III-V semiconductor nanowire (NW) heterostructures have recently emerged as promising candidates to host high-mobility electron channels for future high-frequency, low-energy transistor technologies. The one-dimensional geometry of NWs also makes them attractive for studying quantum confinement effects. Here, we report correlated investigations into the discrete electronic sub-band structure of confined electrons in the channel of Si δ-doped GaAs-GaAs/AlAs core-superlattice NW heterostructures and the associated signatures in low-temperature transport. On the basis of accurate structural and dopant analysis using scanning transmission electron microscopy and atom probe tomography, we calculated the sub-band structure of electrons confined in the NW core and employ a labeling system inspired by atomic orbital notation. Electron transport measurements on top-gated NW transistors at cryogenic temperatures revealed signatures consistent with the depopulation of the quasi-one-dimensional sub-bands, as well as confinement in zero-dimensional-like states due to an impurity-defined background disorder potential. These findings are instructive toward reaching the ballistic transport regime in GaAs-AlGaAs based NW systems.
- Published
- 2017
36. Surface passivation and self-regulated shell growth in selective area-grown GaN–(Al,Ga)N core–shell nanowires
- Author
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Julia Winnerl, Luca Francaviglia, Martin Hetzl, Martin Stutzmann, Max Kraut, Sonja Matich, Anna Fontcuberta i Morral, and Markus Döblinger
- Subjects
010302 applied physics ,Materials science ,Passivation ,Band gap ,Nucleation ,Analytical chemistry ,Nanowire ,Shell (structure) ,Diamond ,Nanotechnology ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystal ,0103 physical sciences ,Scanning transmission electron microscopy ,engineering ,General Materials Science ,0210 nano-technology - Abstract
The large surface-to-volume ratio of GaN nanowires implicates sensitivity of the optical and electrical properties of the nanowires to their surroundings. The implementation of an (Al, Ga) N shell with a larger band gap around the GaN nanowire core is a promising geometry to seal the GaN surface. We investigate the luminescence and structural properties of selective area-grown GaN-(Al, Ga) N core-shell nanowires grown on Si and diamond substrates. While the (Al, Ga) N shell allows a suppression of yellow defect luminescence from the GaN core, an overall intensity loss due to Si-related defects at the GaN/(Al, Ga) N interface has been observed in the case of Si substrates. Scanning transmission electron microscopy measurements indicate a superior crystal quality of the (Al, Ga) N shell along the nanowire side facets compared to the (Al, Ga) N cap at the top facet. A nucleation study of the (Al, Ga) N shell reveals a pronounced bowing of the nanowires along the c-direction after a short deposition time which disappears for longer growth times. This is assigned to an initially inhomogeneous shell nucleation. A detailed study of the proceeding shell growth allows the formulation of a strain-driven self-regulating (Al, Ga) N shell nucleation model.
- Published
- 2017
37. Insight in the 3D morphology of silica-based nanotubes using electron microscopy
- Author
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Wolfgang Schnick, Stefan J. Sedlmaier, Christina Scheu, Teresa Dennenwaldt, Markus Döblinger, and Andreas Wisnet
- Subjects
Materials science ,Morphology (linguistics) ,General Physics and Astronomy ,02 engineering and technology ,Template-free synthesis ,Tuning ,010402 general chemistry ,01 natural sciences ,Focused ion beam ,law.invention ,chemistry.chemical_compound ,Structural Biology ,law ,Scanning transmission electron microscopy ,Silicon tetrachloride ,General Materials Science ,Nanotubes ,Cell Biology ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Crystallography ,Electron tomography ,chemistry ,Chemical engineering ,Transmission electron microscopy ,Electron microscope ,0210 nano-technology ,Beam (structure) - Abstract
Amorphous silica-based nanotubes (SBNTs) were synthesized from phosphoryl triamide, OP(NH2)(3), thiophosphoryl triamide, SP(NH2)(3), and silicon tetrachloride, SiCl4, at different temperatures and with varying amount of the starting material SiCl4 using a recently developed template-free synthesis approach. Diameter and length of the SBNTs are tunable by varying the synthesis parameters. The 3D mesocrystals of the SBNTs were analyzed with focused ion beam sectioning and electron tomography in the transmission electron microscope showing the hollow tubular structure of the SBNTs. The reconstruction of a small SBNT assembly was achieved from a high-angle annular-dark field scanning transmission electron microscopy tilt series containing only thirteen images allowing analyzing beam sensitive material without altering the structure. The reconstruction revealed that the individual nanotubes are forming an interconnected array with an open channel structure. (C) 2016 Elsevier Ltd. All rights reserved.
- Published
- 2016
38. Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs-AlGaAs Core-Shell Nanowires
- Author
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J. Becker, Gerhard Abstreiter, Jochen Bissinger, Sergej Fust, Markus Döblinger, Jonathan J. Finley, Bernhard Loitsch, Gregor Koblmüller, Damon J. Carrad, and Anton Faustmann
- Subjects
Materials science ,Nanowire ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Thermal conductivity ,Seebeck coefficient ,Thermoelectric effect ,thermal conductivity ,General Materials Science ,quantum transport ,business.industry ,Mechanical Engineering ,Quantum oscillations ,Heterojunction ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,0104 chemical sciences ,ddc ,nanowires ,Mechanics of Materials ,Quantum dot ,Raman spectroscopy ,Optoelectronics ,0210 nano-technology ,business ,thermoelectrics - Abstract
Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core-shell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core-shell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65-85 µV K-1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S2 σ ≈ 60 µW m-1 K-2 and S2 G ≈ 0.06 pW K-2 within a single sub-band. Remarkably, these core-shell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m-1 K-1 , about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.
- Published
- 2019
39. Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: AVersatile Approach for their Shape-Controlled Synthesis
- Author
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Lakshminarayana Polavarapu, Maximilian W. Feil, Andrey L. Rogach, En-Ping Yao, He Huang, Alexander F. Richter, Yanxiu Li, Jochen Feldmann, Markus Döblinger, and Yu Tong
- Subjects
Spontaneous Crystallization ,FAPbX3 nanoplatelets ,Materials science ,perovskite nanocrystals ,010402 general chemistry ,01 natural sciences ,Catalysis ,law.invention ,Divalent ,FAPbX3 nanocubes ,law ,Crystallization ,Inert gas ,Perovskite (structure) ,chemistry.chemical_classification ,ligand-assisted reprecipitation ,010405 organic chemistry ,Communication ,General Chemistry ,Organic media ,Communications ,0104 chemical sciences ,Formamidinium ,chemistry ,Nanocrystal ,Chemical engineering ,FAPbX3 nanocubes · FAPbX3 nanoplatelets · ligand-assisted reprecipitation · perovskite nanocrystals · spontaneous crystallization - Abstract
The growing demand for perovskite nanocrystals (NCs) for various applications has stimulated the development of facile synthetic methods. Perovskite NCs have often been synthesized by either ligand‐assisted reprecipitation (LARP) at room temperature or by hot‐injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP affects their stability. Herein, we report on the spontaneous crystallization of perovskite NCs in nonpolar organic media at ambient conditions by simple mixing of precursor–ligand complexes without application of any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+) and Cs+) to divalent (Pb2+) cation–ligand complexes. The precursor–ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and generally applicable for perovskite NCs of different compositions., Faster than fast: Shape‐controlled lead halide perovskite nanocrystals crystallize spontaneously at ambient conditions when precursor–ligand complexes are mixed directly in a nonpolar organic medium. Nanocubes and nanoplatelets have been obtained. This versatile synthetic process is generally applicable for a wide range of halide perovskite nanocrystals.
- Published
- 2019
40. Switching on and off Interlayer Correlations and Porosity in 2D Covalent Organic Frameworks
- Author
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Julian M. Rotter, Torben Sick, Thomas Bein, Dana D. Medina, Timothy Clark, Sharath Kandambeth, Todd B. Marder, Julia Merz, Markus Döblinger, Nicolai N. Bach, and Stephan Reuter
- Subjects
chemistry.chemical_classification ,Imine ,General Chemistry ,Polymer ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Solvent ,chemistry.chemical_compound ,Crystallinity ,Colloid and Surface Chemistry ,chemistry ,Chemical engineering ,Covalent bond ,Thermal stability ,Porosity ,Porous medium - Abstract
Two-dimensional covalent organic frameworks (2D COFs) attract great interest owing to their well-defined pore structure, thermal stability, high surface area, and permanent porosity. In combination with a tunable chemical pore environment, COFs are intriguing candidates for molecular sieving based on selective host-guest interactions. Herein, we report on 2D COF structures capable of reversibly switching between a highly correlated crystalline, porous and a poorly correlated, nonporous state by exposure to external stimuli. To identify COF structures with such dynamic response, we systematically studied the structural properties of a family of two-dimensional imine COFs comprising tris(4-aminophenyl)benzene (TAPB) and a variety of dialdehyde linear building blocks including terephthalaldehyde (TA) and dialdehydes of thienothiophene (TT), benzodithiophene (BDT), dimethoxybenzodithiophene (BDT-OMe), diethoxybenzodithiophene (BDT-OEt), dipropoxybenzodithiophene (BDT-OPr), and pyrene (Pyrene-2,7). TAPB-COFs consisting of linear building blocks with enlarged π-systems or alkoxy functionalities showed significant stability toward exposure to external stimuli such as solvents or solvent vapors. In contrast, TAPB-COFs containing unsubstituted linear building blocks instantly responded to exposure to these external stimuli by a drastic reduction in COF layer correlation, long-range order, and porosity. To reverse the process we developed an activation procedure in supercritical carbon dioxide (scCO2) as a highly efficient means to revert fragile nonporous and amorphous COF polymers into highly crystalline and open porous frameworks. Strikingly, the framework structure of TAPB-COFs responds dynamically to such chemical stimuli, demonstrating that their porosity and crystallinity can be reversibly controlled by alternating steps of solvent stimuli and scCO2 activation.
- Published
- 2019
41. Tuning Lasing Emission towards Long Wavelengths in GaAs-(In,Al)GaAs Core-Multishell Nanowires
- Author
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Thomas Stettner, Paul Schmiedeke, Andreas Thurn, Markus Döblinger, Jochen Bissinger, Sonja Matich, Daniel Ruhstorfer, Hubert Riedl, Jonathan J. Finley, and Gregor Koblmueller
- Published
- 2019
42. Siliciumdioxidwachstum auf DNA‐Origamitemplaten durch Sol‐Gel‐Chemie
- Author
-
Tim Liedl, Markus Döblinger, Linh Nguyen, and Amelie Heuer-Jungemann
- Subjects
Materials science ,Polymer chemistry ,DNA origami ,02 engineering and technology ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Published
- 2018
43. Targeted Fe‐Doping of Ni−Al Catalysts via the Surface Redox Reaction Technique for Unravelling its Promoter Effect in the CO 2 Methanation Reaction
- Author
-
Hannah M. S. Augenstein, Franziska Hnyk, Markus Döblinger, Olaf Hinrichsen, Klaus Köhler, and Thomas Burger
- Subjects
Inorganic Chemistry ,Materials science ,Chemical engineering ,Methanation ,Organic Chemistry ,Doping ,Physical and Theoretical Chemistry ,Redox ,Catalysis ,ddc - Published
- 2018
44. Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy
- Author
-
Gregor Koblmüller, Daniel Ruhstorfer, H. Riedl, Markus Döblinger, Sonja Matich, Armin Lang, and Jonathan J. Finley
- Subjects
Surface diffusion ,Diffraction ,Materials science ,business.industry ,Mechanical Engineering ,Nanowire ,Nucleation ,Bioengineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Aspect ratio (image) ,ddc ,0104 chemical sciences ,Mechanics of Materials ,Scanning transmission electron microscopy ,Optoelectronics ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Spectroscopy ,Molecular beam epitaxy - Abstract
We report a comprehensive study of the growth dynamics in highly periodic, composition tunable InAsSb nanowire (NW) arrays using catalyst-free selective area molecular beam epitaxy. Employing periodically patterned SiO2-masks on Si (111) with various mask opening sizes (20–150 nm) and pitches (0.25–2 μm), high NW yield of >90% (irrespective of the InAsSb alloy composition) is realized by the creation of an As-terminated 1 × 1-Si(111) surface prior to NW nucleation. While the NW aspect ratio decreases continually with increasing Sb content (x Sb from 0% to 30%), we find a remarkable dependence of the aspect ratio on the mask opening size yielding up to ∼8-fold increase for openings decreasing from 150 to 20 nm. The effects of the interwire separation (pitch) on the NW aspect ratio are strongest for pure InAs NWs and gradually vanish for increasing Sb content, suggesting that growth of InAsSb NW arrays is governed by an In surface diffusion limited regime even for the smallest investigated pitches. Compositional analysis using high-resolution x-ray diffraction reveals a substantial impact of the pitch on the alloy composition in homogeneous InAsSb NW arrays, leading to much larger x Sb as the pitch increases due to decreasing competition for Sb adatoms. Scanning transmission electron microscopy and associated energy-dispersive x-ray spectroscopy performed on the cross-sections of individual NWs reveal an interesting growth-axis dependent core–shell like structure with a discontinuous few-nm thick Sb-deficient coaxial boundary layer and six Sb-deficient corner bands. Further analysis evidences the presence of a nanoscale facet at the truncation of the (111)B growth front and {1-10} sidewall surfaces that is found responsible for the formation of the characteristic core–shell structure.
- Published
- 2021
45. Tuning the Optical Properties of Perovskite Nanoplatelets through Composition and Thickness by Ligand-Assisted Exfoliation
- Author
-
Verena A. Hintermayr, Markus Döblinger, Jochen Feldmann, Jasmina A. Sichert, Yu Tong, Alexander F. Richter, Lakshminarayana Polavarapu, Florian Ehrat, Alexander S. Urban, and Willem Vanderlinden
- Subjects
Materials science ,Ligand ,Mechanical Engineering ,Radiative decay ,Halide ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Exfoliation joint ,0104 chemical sciences ,Wavelength ,Chemical engineering ,Nanocrystal ,Mechanics of Materials ,Quantum dot ,General Materials Science ,0210 nano-technology ,Perovskite (structure) - Abstract
High-quality hybrid halide perovskite nanocrystals are fabricated through a simple, versatile, and efficient two-step process involving a dry step followed by a ligand-assisted liquid-phase exfoliation step. The emission wavelength of the resulting nanocrystals can be tuned either through composition by varying the halide content or by reducing their thickness.
- Published
- 2016
46. The Native Material Limit of Electron and Hole Mobilities in Semiconductor Nanowires
- Author
-
Florian J. R. Schülein, Lisa Janker, Matthias Weiß, Hubert J. Krenner, Dominik D. Bühler, Daniel Rudolph, Markus Döblinger, Gerhard Abstreiter, Jonathan J. Finley, Jörg B. Kinzel, Max Bichler, Achim Wixforth, Stefanie Morkötter, Michael Heigl, and Gregor Koblmüller
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,business.industry ,General Engineering ,Nanowire ,Shell (structure) ,General Physics and Astronomy ,02 engineering and technology ,Electron ,Acoustic wave ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,Core (optical fiber) ,Semiconductor ,0103 physical sciences ,ddc:530 ,General Materials Science ,Charge carrier ,0210 nano-technology ,business - Abstract
Piezoelectric surface acoustic waves are employed to induce radio frequency spatiotemporal dynamics of photogenerated electrons and holes in the GaAs core of individual GaAs/AlGaAs core/shell semiconductor nanowires. Comparison of the time-dependent interband optical recombination to numerical simulations allow to determine the charge carrier transport mobilities of electrons, μe = 500–250+500 cm2/(V s), holes, μh = 50–30+50 cm2/(V s) and their ratio μe:μh = (20 ± 5):1. Our method probes carrier transport at low carrier density. Thus, the obtained values represent the native material limit of these nanowires, determined by their structural properties. We show that for near-pristine nanowires, individual twin defects do not significantly affect electrical transport, in strong contrast to polytypic nanowires. In the acoustoelectrically modulated emission, we observe unambiguous signatures of (i) hole localization within long wurtzite-rich segments and (ii) electrons in zinc blende regions being reflected at...
- Published
- 2016
47. Molecular docking sites designed for the generation of highly crystalline covalent organic frameworks
- Author
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Markus Döblinger, Karena W. Chapman, Florian Auras, Timothy Clark, Johannes T. Margraf, Laura Ascherl, Torben Sick, Konstantin Karaghiosoff, Christina Hettstedt, Thomas Bein, Mona Calik, and Saul H. Lapidus
- Subjects
Chemistry ,General Chemical Engineering ,Inorganic chemistry ,Stacking ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Crystal engineering ,01 natural sciences ,0104 chemical sciences ,Crystallinity ,Covalent bond ,Docking (molecular) ,Metal-organic framework ,0210 nano-technology ,Porous medium - Abstract
Covalent organic frameworks (COFs) formed by connecting multidentate organic building blocks through covalent bonds provide a platform for designing multifunctional porous materials with atomic precision. As they are promising materials for applications in optoelectronics, they would benefit from a maximum degree of long-range order within the framework, which has remained a major challenge. We have developed a synthetic concept to allow consecutive COF sheets to lock in position during crystal growth, and thus minimize the occurrence of stacking faults and dislocations. Hereby, the three-dimensional conformation of propeller-shaped molecular building units was used to generate well-defined periodic docking sites, which guided the attachment of successive building blocks that, in turn, promoted long-range order during COF formation. This approach enables us to achieve a very high crystallinity for a series of COFs that comprise tri- and tetradentate central building blocks. We expect this strategy to be transferable to a broad range of customized COFs. Covalent organic frameworks (COFs) are attractive multifunctional porous materials that can be generated with atomic precision. However, endowing them with long-range order—desirable for applications—has remained challenging. Now, propeller-shaped building units have been used that allow consecutive layers to lock in position, resulting in highly crystalline COFs.
- Published
- 2016
48. From Highly Crystalline to Outer Surface-Functionalized Covalent Organic Frameworks—A Modulation Approach
- Author
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Thomas Bein, Harald Budde, Stefan Datz, Torben Sick, Mirjam Dogru, Florian Auras, Markus Döblinger, Mona Calik, and Achim Hartschuh
- Subjects
Chemistry ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Article ,Catalysis ,0104 chemical sciences ,Crystallinity ,Colloid and Surface Chemistry ,Adsorption ,Covalent bond ,Surface modification ,Nanometre ,0210 nano-technology ,Porosity - Abstract
Crystallinity and porosity are of central importance for many properties of covalent organic frameworks (COFs), including adsorption, diffusion, and electronic transport. We have developed a new method for strongly enhancing both aspects through the introduction of a modulating agent in the synthesis. This modulator competes with one of the building blocks during the solvothermal COF growth, resulting in highly crystalline frameworks with greatly increased domain sizes reaching several hundreds of nanometers. The obtained materials feature fully accessible pores with an internal surface area of over 2000 m(2) g(-1). Compositional analysis via NMR spectroscopy revealed that the COF-5 structure can form over a wide range of boronic acid-to-catechol ratios, thus producing frameworks with compositions ranging from highly boronic acid-deficient to networks with catechol voids. Visualization of an -SH-functionalized modulating agent via iridium staining revealed that the COF domains are terminated by the modulator. Using functionalized modulators, this synthetic approach thus also provides a new and facile method for the external surface functionalization of COF domains, providing accessible sites for post-synthetic modification reactions. We demonstrate the feasibility of this concept by covalently attaching fluorescent dyes and hydrophilic polymers to the COF surface. We anticipate that the realization of highly crystalline COFs with the option of additional surface functionality will render the modulation concept beneficial for a range of applications, including gas separations, catalysis, and optoelectronics.
- Published
- 2016
49. Cover Picture: Templated‐Assembly of CsPbBr 3 Perovskite Nanocrystals into 2D Photonic Supercrystals with Amplified Spontaneous Emission (Angew. Chem. Int. Ed. 40/2020)
- Author
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Juan Luis Garcia-Pomar, Luis M. Liz-Marzán, Lakshminarayana Polavarapu, Jochen Feldmann, David Vila-Liarte, Agustín Mihi, He Huang, Maximilian W. Feil, Aurora Manzi, and Markus Döblinger
- Subjects
Amplified spontaneous emission ,Materials science ,Nanocrystal ,business.industry ,Optoelectronics ,Cover (algebra) ,General Chemistry ,Self-assembly ,Photonics ,business ,Catalysis ,Perovskite (structure) - Published
- 2020
50. Titelbild: Template‐basierte Herstellung von 2D‐photonischen Superkristallen mit verstärkter spontaner Emission aus CsPbBr 3 ‐Perowskit‐Nanokristallen (Angew. Chem. 40/2020)
- Author
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Juan Luis Garcia-Pomar, Luis M. Liz-Marzán, He Huang, Agustín Mihi, Maximilian W. Feil, Markus Döblinger, Lakshminarayana Polavarapu, Aurora Manzi, David Vila-Liarte, and Jochen Feldmann
- Subjects
General Medicine - Published
- 2020
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