50 results on '"Leopoldo Molina-Luna"'
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2. Epitaxy Induced Highly Ordered Sm2Co17–SmCo5 Nanoscale Thin-Film Magnets
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Yukiko Takahashi, Robert Eilhardt, Harish K. Singh, Philipp Komissinskiy, Damian Günzing, Leopoldo Molina-Luna, Heiko Wende, Georgia Gkouzia, Debora Motta Meira, Katharina Ollefs, Alexander Zintler, Marton Major, Ruiwen Xie, Iliya Radulov, Hongbin Zhang, Lambert Alff, Johanna Lill, Shalini Sharma, and Konstantin P. Skokov
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010302 applied physics ,Materials science ,Nanocomposite ,Condensed matter physics ,02 engineering and technology ,Coercivity ,021001 nanoscience & nanotechnology ,Magnetocrystalline anisotropy ,01 natural sciences ,Magnetization ,Phase (matter) ,Magnet ,0103 physical sciences ,Scanning transmission electron microscopy ,General Materials Science ,Thin film ,0210 nano-technology - Abstract
Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm2Co17 and SmCo5 phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr)7.5-8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm-Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of Sm2Co17 and SmCo5 phases with 65% Sm2Co17 and 35% SmCo5. The SmCo5 phase is stabilized directly on an Al2O3 substrate up to a thickness of 4 nm followed by a matrix of Sm2Co17 intermixed with SmCo5. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm2Co17 and SmCo5 phases with coherent interfaces result in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm2Co17 and SmCo5 phases at the nanoscale is reflected in the observed magnetocrystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophased magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets.
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- 2021
3. Domain morphology of newly designed lead‐free antiferroelectric NaNbO 3 ‐SrSnO 3 ceramics
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Hui Ding, Leopoldo Molina-Luna, Mao-Hua Zhang, Jurij Koruza, and Hans-Joachim Kleebe
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010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Superlattice ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Hysteresis ,Electron diffraction ,Transmission electron microscopy ,0103 physical sciences ,Domain (ring theory) ,Materials Chemistry ,Ceramics and Composites ,Antiferroelectricity ,0210 nano-technology - Abstract
Reversible antiferroelectric-ferroelectric phase transitions were recently observed in a series of SrSnO3-modified NaNbO3 lead-free antiferroelectric materials, exhibiting well-defined double polarization hysteresis loops at ambient conditions. Here, transmission electron microscopy was employed to investigate the crystallographyand domain configuration of this newly designed system via electron diffraction and centered dark-field imaging. It was confirmed that antiferroelectricity is maintained in all compositions, manifested by the characteristic ¼ superlattice reflections in the electron-diffraction patterns. By investigating the antiferroelectric domains and domain boundaries in NaNbO3, we demonstrate that antiphase boundaries are present and their irregular periodicity is responsible for the streaking features along the ¼ superlattice reflections in the electron-diffraction patterns. The signature domain blocks observed in pure NaNbO3 are maintained in the SrSnO3-modified ceramics, but disappear when the amount of SrSnO3 reaches 7 mol.%. In particular, a well-defined and distinct domain configuration is observed in the NaNbO3 sample modified with 5 mol.% SrSnO3, which presents a parallelogram domain morphology.
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- 2021
4. Electric-field-induced antiferroelectric to ferroelectric phase transition in polycrystalline NaNbO3
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Jurij Koruza, Hui Ding, Mao-Hua Zhang, Leopoldo Molina-Luna, Hans-Joachim Kleebe, Lovro Fulanović, Sonja Egert, and Pedro B. Groszewicz
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010302 applied physics ,Permittivity ,Phase transition ,Materials science ,Polymers and Plastics ,Condensed matter physics ,Metals and Alloys ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Piezoelectricity ,Ferroelectricity ,Electronic, Optical and Magnetic Materials ,Electric field ,0103 physical sciences ,Ceramics and Composites ,Antiferroelectricity ,Crystallite ,0210 nano-technology - Abstract
Electric-field-induced phase transitions are the most important characteristics of antiferroelectric materials. However, in several prototype antiferroelectrics, these transitions are irreversible and the origin of this behavior is poorly understood. This prevents their widespread use, for example, in energy storage and memory applications. Here, we investigated the antiferroelectric-ferroelectric phase transitions in polycrystalline NaNbO3, a material recently suggested as the basis for lead-free antiferroelectrics with high energy storage densities. An irreversible transition from the antiferroelectric state to a new state showing macroscopic piezoelectricity (d33=35 pC/N) was induced at 11.6 kV/mm (room temperature, 1 Hz), accompanied by a 33% drop in permittivity. Microscopically, a change from a translational antiferroelectric domain structure to a wedge-shaped ferroelectric domain structure was observed using transmission electron microscopy. 23Na solid-state nuclear magnetic resonance allowed for a detailed study of the local structure and revealed pure antiferroelectric and coexisting antiferroelectric/ferroelectric nature of the samples before and after the application of an electric field, respectively. Interestingly, despite the large electric fields applied, only 50±5% of the material underwent the antiferroelectric-ferroelectric phase transition, which was related to the material´s microstructure. The temperature- and frequency-dependence of the phase transition was studied and compared to the behavior observed in lead-based antiferroelectric systems.
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- 2020
5. Production of Fe nanoparticles from γ-Fe2O3 by high-pressure hydrogen reduction
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C. A. Schwöbel, Alexander Zintler, Philipp Komissinskiy, Leopoldo Molina-Luna, Oliver Gutfleisch, and I. Dirba
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Coalescence (physics) ,Materials science ,Hydrogen ,General Engineering ,Iron oxide ,Analytical chemistry ,Nanoparticle ,chemistry.chemical_element ,Bioengineering ,02 engineering and technology ,General Chemistry ,Coercivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Particle ,General Materials Science ,Particle size ,0210 nano-technology ,Bar (unit) - Abstract
In this work, the reduction of iron oxide γ-Fe2O3 nanoparticles by hydrogen at high pressures is studied. Increasing the hydrogen pressure enables reduction of γ-Fe2O3 to α-Fe at significantly lower temperatures. At low pressures, a temperature of 390 °C is necessary whereas at 530 bar complete reduction can be realized at temperatures as low as 210 °C. This leads to significant improvement in the final particle morphology, maintaining high surface-to-volume ratio of the nanoparticles with an average size of 47 ± 5 nm which is close to that of the precursor γ-Fe2O3. Neck formation, coalescence and growth during reduction can be significantly suppressed. Investigations of magnetic properties show that saturation magnetization of the reduced α-Fe nanoparticles decreases with particle size from 209 A m2 kg−1 at 390 °C reduction temperature to 204 A m2 kg−1 at 210 °C. Coercivity for the fine iron particles reaches 0.076 T which exceeds the theoretical anisotropy field. This is attributed to nano-scale surface effects.
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- 2020
6. Experimental and theoretical investigation of the chemical exfoliation of Cr-based MAX phase particles
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Anna Regoutz, Delwin Perera, Pardeep K. Thakur, Christina S. Birkel, Minh Hai Tran, Jochen Rohrer, Leopoldo Molina-Luna, Ali Muhammad Malik, Karsten Albe, Michael Dürrschnabel, and Tien-Lin Lee
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Materials science ,Oxide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Isotropic etching ,Exfoliation joint ,0104 chemical sciences ,Carbide ,Inorganic Chemistry ,chemistry.chemical_compound ,Hydrofluoric acid ,chemistry ,Chemical engineering ,MAX phases ,0210 nano-technology ,MXenes ,Chromium carbide - Abstract
Two-dimensional carbides/nitrides, typically called MXenes, are an emerging member of the ever-growing family of two-dimensional materials. The prediction of a ferromagnetic groundstate in chromium-containing MXenes has triggered growing interest in their chemical exfoliation from Cr-based MAX phases. However, the exfoliation poses serious difficulties using standard etching agents such as hydrofluoric acid (HF). Here, we investigate the exfoliability of Cr2GaC particles by chemical etching with aqueous HF both experimentally and theoretically. Structural and microstructural analyses show that the Cr2GaC particles decompose into chromium carbide and oxide without the formation of a Cr-based MXene. A thermodynamic analysis based on ab initio electronic structure calculations reveals that the exfoliation of Cr-based MXene from Cr2GaC by HF-etching is inhibited by more favorable competing reactions. This result confirms the experimental finding and suggests that HF is an unsuitable etching agent for a successful exfoliation of Cr2GaC.
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- 2020
7. Synthesis of Anatase (Core)/Rutile (Shell) Nanostructured TiO2 Thin Films by Magnetron Sputtering Methods for Dye-Sensitized Solar Cell Applications
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Carla Bittencourt, Matthieu Michiels, Pierre-Antoine Cormier, Michael Dürrschnabel, Adriano Panepinto, Leopoldo Molina-Luna, and Rony Snyders
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Anatase ,Materials science ,Shell (structure) ,Energy Engineering and Power Technology ,02 engineering and technology ,Sputter deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Dye-sensitized solar cell ,Chemical engineering ,Rutile ,Materials Chemistry ,Electrochemistry ,Chemical Engineering (miscellaneous) ,Electrical and Electronic Engineering ,High-power impulse magnetron sputtering ,Thin film ,0210 nano-technology - Abstract
Currently, anatase/rutile core/shell structures are accepted as highly efficient building blocks for TiO2-based catalysts or photoelectrodes used in dye-sensitized solar cells (DSSCs). It is unders...
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- 2019
8. Experimental and computational analysis of binary Fe-Sn ferromagnetic compounds
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Tim Helbig, Michael Duerrschnabel, Urban Rohrmann, Rudolf Schäfer, Tom Faske, Ingo Opahle, Wolfgang Donner, Konstantin P. Skokov, Bahar Fayyazi, Konrad Güth, Oliver Gutfleisch, Hongbin Zhang, Leopoldo Molina-Luna, and Ivan Soldatov
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010302 applied physics ,Materials science ,Polymers and Plastics ,Magnetic domain ,Condensed matter physics ,Metals and Alloys ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Magnetocrystalline anisotropy ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetization ,Ferromagnetism ,0103 physical sciences ,Ceramics and Composites ,Density functional theory ,0210 nano-technology ,Anisotropy ,Crystal twinning ,Spontaneous magnetization - Abstract
Ferromagnetic Fe3Sn, Fe5Sn3 and Fe3Sn2 single crystals were synthesized using the reactive flux technique. Derived from single crystal x-ray diffraction and Transmission Electron Microscopy (TEM), a new structural model is proposed for the Fe5Sn3 crystals - the threefold twinning of an orthorhombic unit cell with (3 + 1) dimensional space group Pbcm(α00)0s0. The spontaneous magnetization (Ms) and the anisotropy constants K1 and K2 of Fe3Sn, Fe5Sn3 and Fe3Sn2 single crystals were determined in a wide temperature range using M(H) dependencies and a modified Sucksmith-Thompson technique. Ms and K1 were also evaluated in the framework of Density Functional Theory (DFT) and an overall good agreement was observed between the calculated and experimental results. Furthermore, a critical evaluation of different analytical models for the assessment of magnetocrystalline anisotropy was performed, which are restricted to the analysis of uniaxial magnetic domain patterns, and it is shown that such high-throughput techniques can lead to unrealistic results. Finally, a DFT high-throughput screening of the Fe-Sn phase diagram was used to identify Fe-Sn based phases with potential to be stabilized upon alloying, and their magnetization and magnetocrystalline anisotropy were evaluated. The results show that a similar strong anisotropy as observed in Fe3Sn may also be found in other Fe-Sn based phases, having higher potential to be used as hard magnetic material.
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- 2019
9. Conformal Solution Deposition of Pt-Pd Titania Nanocomposite Coatings for Light-Assisted Formic Acid Electro-Oxidation
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V. V. Sikolenko, Gumaa A. El-Nagar, Alexander Zintler, Chiara Pasquini, Falk Muench, Tim Tichter, Iver Lauermann, Ulrike Kunz, Leopoldo Molina-Luna, and Christina Roth
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Nanocomposite ,Materials science ,Conformal coating ,Substrate (chemistry) ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Nanocrystalline material ,0104 chemical sciences ,Adsorption ,Chemical engineering ,General Materials Science ,0210 nano-technology ,Layer (electronics) ,Chemical bath deposition - Abstract
Many nanofabrication processes require sophisticated equipment, elevated temperature, vacuum or specific atmospheric conditions, templates, and exotic chemicals, which severely hamper their implementation in real-world applications. In this study, we outline a fully wet-chemical procedure for equipping a 3D carbon felt (CF) substrate with a multifunctional, titania nanospike-supported Pt-Pd nanoparticle (Pt-Pd-TiO2@CF) layer in a facile and scalable manner. The nanostructure, composition, chemical speciation, and formation of the material was meticulously investigated, evidencing the conformal coating of the substrate with a roughened layer of nanocrystalline rutile spikes by chemical bath deposition from Ti3+ solutions. The spikes are densely covered by bimetallic nanoparticles of 4.4 ± 1.1 nm in size, which were produced by autocatalytic Pt deposition onto Pd seeds introduced by Sn2+ ionic layer adsorption and reaction. The as-synthesized nanocomposite was applied to the (photo)electro-oxidation of formic acid (FA), exhibiting a superior performance compared to Pt-plated, Pd-seeded CF (Pt-Pd@CF) and commercial Pt-C, indicating the promoting electrocatalytic role of the TiO2 support. Upon UV-Vis illumination, the performance of the Pt-Pd-TiO2@CF electrode is remarkably increased (22-fold), generating a current density of 110 mA cm-2, distinctly outperforming titania-free Pt-Pd@CF (5 mA cm-2) and commercial Pt-C (6 mA cm-2) reference catalysts. In addition, the Pt-Pd-TiO2@CF showed a much better stability, characterized by a very high poisoning tolerance for in situ-generated CO intermediates, whose formation is hindered in the presence of TiO2. This overall performance boost is attributed to a dual enhancement mechanism (∼30% electrocatalytic and ∼70% photoelectrocatalytic). The photogenerated electrons from the TiO2 conduction band enrich the electron density of the Pt nanoparticles, promoting the generation of active oxygen species on their surfaces from adsorbed oxygen and water molecules, which facilitate the direct FA electro-oxidation into CO2.
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- 2019
10. Porosity-tuned thermal conductivity in thermoelectric Al-doped ZnO thin films grown by mist-chemical vapor deposition
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Ataru Ichinose, Chaoyang Li, Junichiro Shiomi, Paolo Mele, Koji Miyazaki, Leopoldo Molina-Luna, Toshiyuki Kawaharamura, Janne-Petteri Niemelä, Takafumi Oyake, Maarit Karppinen, and Shrikant Saini
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Materials science ,ta221 ,Oxide ,02 engineering and technology ,Chemical vapor deposition ,01 natural sciences ,Thermoelectric effect ,Pulsed laser deposition ,chemistry.chemical_compound ,Thermal conductivity ,Zinc oxide ,0103 physical sciences ,Materials Chemistry ,Figure of merit ,Thin film ,010302 applied physics ,business.industry ,Doping ,Metals and Alloys ,Oxides ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,Mist-chemical vapor deposition ,0210 nano-technology ,business ,Porosity - Abstract
The potential of thermoelectric thin films lies in wide range of applications from micro-energy harvesting to the sensors. For this, it is essential to have high power factor and ultra-low thermal conductivity which have been reported in thin films produced by expensive vacuum techniques. However, for practical applications, it is essential to use inexpensive technique to grow thin film in large area. In this direction, we report the use of mist-chemical vapor deposition (CVD) technique to develop oxide thin films for thermoelectric application. We grow c-axis oriented nano-porous thin films of 2% Al-doped ZnO (AZO). These nano-porous films have enhance phonon scattering which results in the depression of thermal conductivity (κ) while maintaining similar order of magnitude of power factor as reported in dense films prepared by vacuum techniques. For example, κ300K decreases from 6.5 W/m.K for dense thin film (porosity = 7.9%) grown by pulsed laser deposition to 5.54 W/m.K for porous film (porosity = 24.2%) grown by mist-CVD while maintaining the power factor of similar order of magnitude for AZO film deposited on SrTiO3. The depression of thermal conductivity in porous films may lead to higher figure of merit which is promising for practical applications of thermoelectric oxide films.
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- 2019
11. Shape-Selective Electroless Plating within Expanding Template Pores: Etching-Assisted Deposition of Spiky Nickel Nanotube Networks
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Michael Dürrschnabel, Wolfgang Ensinger, Markus Antoni, Ulrike Kunz, Leopoldo Molina-Luna, Tim Boettcher, Tobias Stohr, Sandra Schaefer, and Falk Muench
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Nanotube ,Materials science ,Nanostructure ,Nucleation ,Nanoparticle ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Surfaces and Interfaces ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Nickel ,Template ,chemistry ,Etching (microfabrication) ,Plating ,Electrochemistry ,General Materials Science ,0210 nano-technology ,Spectroscopy - Abstract
Nano-objects are favored structures for applications such as catalysis and sensing. Although they already provide a large surface-to-volume ratio, this ratio can be further increased by shape-selective plating of the nanostructure surfaces. This process combines the conformity of autocatalytic deposition with the defined nucleation and growth characteristics of colloidal nanoparticle syntheses. However, many aspects of such reactions are still not fully understood. In this study, we investigate in detail the growth of spiky nickel nanotubes in polycarbonate template membranes. One distinctive feature of our synthesis is the simultaneous growth of nanospikes on both the inside and outside of nanotubes while the tubes are still embedded in the polymer. This is achieved by combining the plating process with locally enhanced in situ etching of the poylmer template, for which we propose a theory. Electron microscopy investigations reveal twinning defects as the driving force for the growth of crystalline nanospikes. Deposit crystallinity is ensured by the reducing agent hydrazine. Iminodiacetic acid is not only used as a complexing agent during synthesis but apparently also acts as a capping agent and limits random nucleation on the spike facets. Finally, we apply our synthesis to templates with interconnected pores to obtain free-standing spiky nickel nanotube networks, demonstrating its ability to homogeneously coat substrates with extended inner surfaces and to operate in nanoscale confinement.
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- 2019
12. Sol–gel based synthesis and enhanced processability of MAX phase Cr2GaC
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Christina S. Birkel, Alexander Zintler, Maren Lepple, Ulf Wiedwald, Lothar Bischoff, Jan P. Siebert, and Leopoldo Molina-Luna
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Materials science ,Aqueous solution ,Oxide ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Transmission electron microscopy ,Phase (matter) ,Materials Chemistry ,MAX phases ,0210 nano-technology ,Wet chemistry ,Sol-gel - Abstract
MAX phases are typically prepared by high-temperature (oftentimes high-pressure) solid-state methods. Here, we report a new wet chemistry based synthesis technique starting from an aqueous solution of metal nitrates and citric acid to prepare MAX phase Cr2GaC. This solution-processable precursor mixture has the potential to be easily scaled, painted, printed or fabricated onto supports – an advantage that is demonstrated by the formation of hollow carbon microspheres which are decorated with Cr2GaC particles. A small amount of chromium carbide and oxide remains in the product, however, the amount of the latter can be reduced by a larger excess in citric acid in the precursor gel. The transformation mechanism of the initial amorphous gel into highly crystalline and anisotropic MAX phase particles is investigated by detailed thermal analysis. Transmission electron microscopy studies are conducted to elucidate the microstructure of the sol–gel-prepared particles as well as the decorated hollow microspheres. From magnetic susceptibility measurements, the density of states at the Fermi level is deduced reflecting the quality of the Pauli paramagnet Cr2GaC.
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- 2019
13. Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects
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Navid Shayanfar, Konstantin P. Skokov, David Koch, Andreas Taubel, Franziska Scheibel, Oliver Gutfleisch, Nagaarjhuna A. Kani, Lukas Pfeuffer, Esmaeil Adabifiroozjaei, Jonas Lemke, Leopoldo Molina-Luna, and S. Riegg
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010302 applied physics ,Condensed Matter - Materials Science ,Materials science ,Polymers and Plastics ,Orders of magnitude (temperature) ,Metals and Alloys ,Thermodynamics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Isothermal process ,Electronic, Optical and Magnetic Materials ,Intergranular fracture ,Stress (mechanics) ,Diffusionless transformation ,0103 physical sciences ,Ceramics and Composites ,Magnetic refrigeration ,Grain boundary ,0210 nano-technology - Abstract
Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response to magnetic fields and uniaxial stress which can be utilized in single caloric or multicaloric cooling concepts for energy-efficient and sustainable refrigeration. However, during cyclic operation these alloys suffer from structural and functional fatigue as a result of their high intrinsic brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure design strategy which simultaneously improves cyclic stability and maintains the excellent magnetocaloric and elastocaloric properties. Our results reveal that precipitation of a strongly Fe-enriched and In-depleted coherent secondary gamma-phase at grain boundaries can ensure excellent mechanical stability by hindering intergranular fracture during cyclic loading. In this way, a large elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without structural or functional degradation, which corresponds to an increase of the cyclic stability by more than three orders of magnitude as compared to single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the dual-phase material when the secondary gamma-phase is exclusively formed at grain boundaries as the martensitic transformation within the Heusler matrix is barely affected. This way, an adiabatic temperature change of -3 K and an isothermal entropy change of 15 $Jkg^{-1}K^{-1}$ was obtained in 2 T for dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other single caloric and mutlicaloric materials, therewith paving the way for solid-state caloric cooling applications.
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- 2021
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14. Role of Oxygen Defects in Conductive-Filament Formation in Y2O3 -Based Analog RRAM Devices as Revealed by Fluctuation Spectroscopy
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Jens Müller, Nico Kaiser, S. U. Sharath, Stefan Petzold, Eszter Piros, Martin Lonsky, Leopoldo Molina-Luna, Christian Wenger, Robert Eilhardt, Tobias Vogel, Lambert Alff, and Alexander Zintler
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Resistive touchscreen ,Materials science ,Condensed matter physics ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Noise (electronics) ,Oxygen ,Resistive random-access memory ,Protein filament ,chemistry ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Spectroscopy ,Yttria-stabilized zirconia ,Voltage - Abstract
Low-frequency noise in Y2O3-based resistive random-access memory devices with analog switching is studied at intermediate resistive states and as a function of dc cycling. A universal 1/f(alpha)-type behavior is found, with a frequency exponent of alpha approximate to 1.2 that is independent of the applied reset voltage or the device resistance and is attributed to the intrinsic abundance of oxygen vacancies unique to the structure of yttria. Remarkably, the noise magnitude in the high resistive state systematically decreases through dc training. This effect is attributed to the stabilization of the conductive filament via the consumption of oxygen vacancies, thus reducing the number of active fluctuators in the vicinity of the filament.
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- 2020
15. Induction of uniaxial anisotropy by controlled phase separation in Y-Co thin films
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Konstantin P. Skokov, Leopoldo Molina-Luna, Philipp Komissinskiy, Iliya Radulov, Hongbin Zhang, Alexander Zintler, Shalini Sharma, Lambert Alff, Marton Major, Dominik Ohmer, Ulrike Kunz, and Bai-Xiang Xu
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Materials science ,Condensed matter physics ,02 engineering and technology ,Coercivity ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Lattice constant ,Magnet ,Phase (matter) ,0103 physical sciences ,Hardening (metallurgy) ,Thin film ,010306 general physics ,0210 nano-technology ,Anisotropy ,Molecular beam epitaxy - Abstract
In this study, molecular beam epitaxy is utilized to stabilize a nanostructured thin-film magnet consisting of a soft magnetic Y2Co17 exchange coupled to hard magnetic YCo5. While, typically, a phase decomposition can be obtained in rare-earth cobalt systems only by the addition of further elements like Cu, Fe, and Zr and complex heat treatments, here we directly induce phase separation by growth kinetics. The resulting nanoscale architecture, as revealed by cross-sectional transmission electron microscopy, is composed of a network of coherently interlinked and aligned Y2Co17 and YCo5 building blocks. The formation of coherent precipitations is facilitated by the perfectly matching lattice constants, atomic species, and crystal symmetry of the two phases with vastly different magnetocrystalline anisotropies. The hard magnetic phase induces an aligned uniaxial anisotropy in Y2Co17, resulting in substantial coercivity associated with enhanced energy products. This work highlights the importance of thin-film epitaxy in understanding magnetic hardening mechanisms and suggests strategies for a rational design of future sustainable magnetic systems.
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- 2020
16. Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion
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Min Yi, Yevheniy Pivak, Alexander Zintler, Shuai Wang, Leopoldo Molina-Luna, Qiang Xu, Hector H. Perez-Garza, Ronald G. Spruit, Matias Acosta, and Bai-Xiang Xu
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Materials science ,Science ,Diffusion ,Flexoelectricity ,General Physics and Astronomy ,02 engineering and technology ,Dielectric ,7. Clean energy ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,chemistry.chemical_compound ,Phase (matter) ,0103 physical sciences ,010306 general physics ,Polarization (electrochemistry) ,lcsh:Science ,Multidisciplinary ,General Chemistry ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Sodium bismuth titanate ,chemistry ,Chemical physics ,Strontium titanate ,lcsh:Q ,0210 nano-technology - Abstract
Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST) core–shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core–shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion., The limited number of materials with a switchable electrical polarization available for applications can be increased by exploiting the flexoelectric effect. Here, switchable polarization in nanoparticles induced by an elemental distribution dependent strain gradient up to 800 °C is demonstrated.
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- 2018
17. Adding a New Member to the MXene Family: Synthesis, Structure, and Electrocatalytic Activity for the Hydrogen Evolution Reaction of V4C3Tx
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Ali Shahraei, Michael Dürrschnabel, Ulrike I. Kramm, Timo Schäfer, Leopoldo Molina-Luna, Christina S. Birkel, and Minh Hai Tran
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Materials science ,Energy Engineering and Power Technology ,02 engineering and technology ,Nitride ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Carbide ,Chemical engineering ,Materials Chemistry ,Electrochemistry ,Chemical Engineering (miscellaneous) ,Hydrogen evolution ,MAX phases ,Electrical and Electronic Engineering ,0210 nano-technology ,MXenes - Abstract
Two-dimensional transition-metal-based carbides (or nitrides), so-called MXenes, that can be derived from the three-dimensional MAX phases, have attracted considerable attention throughout the past...
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- 2018
18. Structural, magnetic and electrical transport properties of non-conventionally prepared MAX phases V2AlC and (V/Mn)2AlC
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Ruslan Salikhov, Christina S. Birkel, Christin M. Hamm, Leopoldo Molina-Luna, Michael Farle, Michael Dürrschnabel, Detlef Spoddig, and Ulf Wiedwald
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010302 applied physics ,Materials science ,Condensed matter physics ,Magnetic moment ,Spark plasma sintering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Paramagnetism ,Ferromagnetism ,Phase (matter) ,0103 physical sciences ,Atom ,Materials Chemistry ,General Materials Science ,MAX phases ,Thin film ,0210 nano-technology - Abstract
A plethora of magnetic ground states along with intriguing magnetic properties have been reported in thin films of Mn-containing MAX phases. However, fewer results and therefore less knowledge in the area of bulk magnetic MAX phases exist resulting in many open research questions that still remain unanswered. Synthesis of high quality materials is key and is here achieved for bulk V2AlC and its Mn-doped analogs by means of microwave heating and spark plasma sintering. The obtained materials are carefully characterized by structural and microstructural investigations resulting in an average Mn-content of 2% corresponding to the mean chemical composition of (V0.96±0.02Mn0.04±0.02)2AlC in the Mn-doped V2AlC samples. While the parent MAX phase as well as the sample with the nominally lowest Mn-content are obtained essentially single-phase, samples with higher Mn-levels exhibit Mn-rich side phases. These are most likely responsible for the ferromagnetic behavior of the corresponding bulk materials. Besides, we show Pauli paramagnetism of the parent compound V2AlC and a combination of Pauli and Langevin paramagnetism in (V0.96±0.02Mn0.04±0.02)2AlC. For the latter, a magnetic moment of μM = 0.2(2) μB per M atom can be extracted.
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- 2018
19. Designing properties of (Na1/2Bix)TiO3-based materials through A-site non-stoichiometry
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Leopoldo Molina-Luna, Hans-Joachim Kleebe, Matias Acosta, Sebastian Steiner, Herbert Hutter, Till Frömling, Kyle G. Webber, Azatuhi Ayrikyan, Daniel Bremecker, and Michael Dürrschnabel
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010302 applied physics ,Materials science ,Orders of magnitude (temperature) ,Diffusion ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Grain size ,Crystallography ,Chemical physics ,visual_art ,0103 physical sciences ,Materials Chemistry ,visual_art.visual_art_medium ,Grain boundary diffusion coefficient ,Grain boundary ,Ceramic ,0210 nano-technology ,Order of magnitude - Abstract
Point defects largely determine the properties of functional oxides. So far, limited knowledge exists on the impact of cation vacancies on electroceramics, especially in (Na1/2Bi1/2)TiO3 (NBT)-based materials. Here, we report on the drastic effect of A-site non-stoichiometry on the cation diffusion and functional properties in the representative ferroelectric (Na1/2Bi1/2)TiO3–SrTiO3 (NBT–ST). Experiments on NBT/ST bilayers and NBT–ST with Bi non-stoichiometry reveal that Sr2+-diffusion is enhanced by up to six orders of magnitude along the grain boundaries in Bi-deficient material as compared to Bi-excess material with values of grain boundary diffusion ∼10−8 cm2 s−1 and ∼10−13 cm2 s−1 in the bulk. This also means a nine orders of magnitude higher diffusion coefficient compared to reports from other Sr-diffusion coefficients in ceramics. Bi-excess leads to the formation of a material with a core–shell microstructure. This results in 38% higher strain and one order of magnitude lower remanent polarization. In contrast, Bi-deficiency leads to a ceramic with a grain size six times larger than in the Bi-excess material and homogeneous distribution of compounds. Thus, the work sheds light on the rich opportunities that A-site stoichiometry offers to tailor NBT-based materials microstructure, transport properties, and electromechanical properties.
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- 2018
20. Molecular dynamics simulation of crystal structure and heat capacity in perovskite-type molybdates SrMoO3 and BaMoO3
- Author
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Shuai Wang, Leopoldo Molina-Luna, I. Dirba, Philipp Komissinskiy, Kathrin Hofmann, Lambert Alff, Barbara Albert, and Mahdad Mohammadi
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Materials science ,General Computer Science ,General Physics and Astronomy ,Thermodynamics ,02 engineering and technology ,General Chemistry ,Crystal structure ,Atmospheric temperature range ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Heat capacity ,Thermal expansion ,0104 chemical sciences ,Computational Mathematics ,symbols.namesake ,Molecular dynamics ,Mechanics of Materials ,symbols ,General Materials Science ,Crystallite ,0210 nano-technology ,Debye model ,Perovskite (structure) - Abstract
A molecular dynamics simulation approach is applied to investigate thermal expansion of the lattice parameters and heat capacities of SrMoO3 and BaMoO3 perovskite-type molybdates in the temperature range between 300 and 1000 K. The meaningful shape of the pairwise potential for SrMoO3 and BaMoO3 is achieved by fitting their lattice parameters to those of the high-purity polycrystalline powders synthesized via reduction of their respective scheelite precursors in hydrogen atmosphere at high pressure. The approach is validated by the simulated temperature dependences of the heat capacity, which follow the reported experimental data near and above the Debye temperature.
- Published
- 2021
21. FIB based fabrication of an operative Pt/HfO2/TiN device for resistive switching inside a transmission electron microscope
- Author
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S. U. Sharath, Ulrike Kunz, Leopoldo Molina-Luna, S. Vogel, Lambert Alff, Yevheniy Pivak, Hans-Joachim Kleebe, Alexander Zintler, and Erwin Hildebrandt
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010302 applied physics ,Microelectromechanical systems ,Materials science ,Fabrication ,business.industry ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Focused ion beam ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Anode ,Resistive random-access memory ,Lamella (surface anatomy) ,Nanoelectronics ,chemistry ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Tin ,Instrumentation - Abstract
Recent advances in microelectromechanical systems (MEMS) based chips for in situ transmission electron microscopy are opening exciting new avenues in nanoscale research. The capability to perform current-voltage measurements while simultaneously analyzing the corresponding structural, chemical or even electronic structure changes during device operation would be a major breakthrough in the field of nanoelectronics. In this work we demonstrate for the first time how to electrically contact and operate a lamella cut from a resistive random access memory (RRAM) device based on a Pt/HfO2/TiN metal-insulator-metal (MIM) structure. The device was fabricated using a focused ion beam (FIB) instrument and an in situ lift-out system. The electrical switching characteristics of the electron-transparent lamella were comparable to a conventional reference device. The lamella structure was initially found to be in a low resistance state and could be reset progressively to higher resistance states by increasing the positive bias applied to the Pt anode. This could be followed up with unipolar set/reset operations where the current compliance during set was limited to 400 µA. FIB structures allowing to operate and at the same time characterize electronic devices will be an important tool to improve RRAM device performance based on a microstructural understanding of the switching mechanism.
- Published
- 2017
22. Kirkendall Effect vs Corrosion of Silver Nanocrystals by Atomic Oxygen: From Solid Metal Silver to Nanoporous Silver Oxide
- Author
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Eric Gautron, Abdel-Aziz El Mel, Leopoldo Molina-Luna, Nicolas Stephant, Yousef Haik, Pierre-Yves Tessier, Nouar Tabet, Romain Gautier, Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Department of Material- and Geosciences, Darmstadt, and Technische Universität Darmstadt (TU Darmstadt)
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Materials science ,Kirkendall effect ,Oxide ,Nanowire ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Silver nanoparticle ,Corrosion ,chemistry.chemical_compound ,Physical and Theoretical Chemistry ,ComputingMilieux_MISCELLANEOUS ,Nanoporous ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,chemistry ,Nanocrystal ,13. Climate action ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,0210 nano-technology ,Silver oxide - Abstract
The corrosion of silver upon exposure to atomic oxygen is a unique effect reported in the 1980s and was highly studied to overcome the fast degradation of space shuttles in low earth orbit. In this work, we explored the conversion mechanisms of nanostructures from solid silver to nanoporous silver oxide upon exposure to radiofrequency air plasma. A broad panel of silver nanostructures with various shapes, sizes, and morphologies were considered to carefully examine the different stages of the oxidation process which evolve according to the considered model-system (e.g., nanosphere, nanowire, nanocube, or nanotriangle). Through a set of time-lapse studies and very specific experiments, we explained the generation of nanoporosity according to a mechanism based on two effects: (i) the high strain in the oxide shell generated as a consequence to the oxidation process and amplified by the bombardment of the material with the energetic species present in the radio frequency air plasma and (ii) the Kirkendall ef...
- Published
- 2017
23. Atomic structure and domain wall pinning in samarium-cobalt-based permanent magnets
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Leopoldo Molina-Luna, Min Yi, Hans-Joachim Kleebe, Oliver Gutfleisch, K. Uestuener, M. Katter, Michael Duerrschnabel, Bai-Xiang Xu, and M. Liesegang
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010302 applied physics ,Multidisciplinary ,Materials science ,Nanostructure ,Dopant ,Condensed matter physics ,Science ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Coercivity ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,Corrosion ,Domain wall (magnetism) ,Samarium cobalt ,Magnet ,0103 physical sciences ,0210 nano-technology - Abstract
A higher saturation magnetization obtained by an increased iron content is essential for yielding larger energy products in rare-earth Sm2Co17-type pinning-controlled permanent magnets. These are of importance for high-temperature industrial applications due to their intrinsic corrosion resistance and temperature stability. Here we present model magnets with an increased iron content based on a unique nanostructure and -chemical modification route using Fe, Cu, and Zr as dopants. The iron content controls the formation of a diamond-shaped cellular structure that dominates the density and strength of the domain wall pinning sites and thus the coercivity. Using ultra-high-resolution experimental and theoretical methods, we revealed the atomic structure of the single phases present and established a direct correlation to the macroscopic magnetic properties. With further development, this knowledge can be applied to produce samarium cobalt permanent magnets with improved magnetic performance., Understanding the factors that determine the properties of permanent magnets, which play a central role in many industrial applications, can help in improving their performance. Here, the authors study how changes in the iron content affect the microstructure of samarium cobalt magnets.
- Published
- 2017
24. Elucidating structural order and disorder phenomena in mullite-type Al4B2O9 by automated electron diffraction tomography
- Author
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Reinhard B. Neder, Ute Kolb, Bastian Barton, Thorsten M. Gesing, Haishuang Zhao, Hans-Joachim Kleebe, Hartmut Schneider, Leopoldo Molina-Luna, Reinhard X. Fischer, K. Hoffmann, and Yaşar Krysiak
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Diffraction ,Reflection high-energy electron diffraction ,Materials science ,Gas electron diffraction ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Diffraction tomography ,Crystallography ,Electron diffraction ,Materials Chemistry ,Ceramics and Composites ,Physical and Theoretical Chemistry ,0210 nano-technology ,Superstructure (condensed matter) ,Electron backscatter diffraction - Abstract
The crystal structure and disorder phenomena of Al4B2O9, an aluminum borate from the mullite-type family, were studied using automated diffraction tomography (ADT), a recently established method for collection and analysis of electron diffraction data. Al4B2O9, prepared by sol-gel approach, crystallizes in the monoclinic space group C2/m. The ab initio structure determination based on three-dimensional electron diffraction data from single ordered crystals reveals that edge-connected AlO6 octahedra expanding along the b axis constitute the backbone. The ordered structure (A) was confirmed by TEM and HAADF-STEM images. Furthermore, disordered crystals with diffuse scattering along the b axis are observed. Analysis of the modulation pattern implies a mean superstructure (AAB) with a threefold b axis, where B corresponds to an A layer shifted by ½a and ½c. Diffraction patterns simulated for the AAB sequence including additional stacking disorder are in good agreement with experimental electron diffraction patterns.
- Published
- 2017
25. Multilayer lead-free piezoceramic composites: Influence of co-firing on microstructure and electromechanical behavior
- Author
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Azatuhi Ayrikyan, Michael Duerrschnabel, Sebastian Steiner, Leopoldo Molina-Luna, Kyle G. Webber, Florian Weyland, and Jurij Koruza
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010302 applied physics ,Materials science ,Composite number ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Microanalysis ,Grain size ,Composite structure ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Ceramic ,Composite material ,0210 nano-technology ,Porosity - Abstract
In this study lead-free 2-2 and 0-3 ceramic/ceramic composites comprised of the non-ergodic relaxor 0.93(Bi1/2Na1/2)TiO3–0.07BaTiO3 and ergodic relaxor 0.94Bi0.5(Na0.75K0.25)0.5TiO3–0.06BiAlO3 were investigated. The macroscopic electromechanical behavior was characterized as a function of continuent content,revealing an enhancement in the unipolar strain from the multilayer composite structure. Systematic evaluation of the effects of co-sintering on microstructural properties, such as grain size and porosity, revealed potential mechanisms by which the increase in unipolar strain was achieved. In addition, interdiffusion between the constituents was observed, providing evidence for the formation of a functionally graded ceramic by co-sintering. These data are contrasted with highresolution energy dispersive X-ray microanalysis for measurement of chemical composition across the interface of 2-2 ceramics. These findings provide insight into how synthesis routes can be optimized for tailoring the enhancement of electromechanical properties of lead-free electroceramic composite systems.
- Published
- 2017
26. Nanoscale Iron Nitride, ε-Fe3N: Preparation from Liquid Ammonia and Magnetic Properties
- Author
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Hans-Joachim Kleebe, Barbara Albert, Anne-Marie Zieschang, Michael Dürrschnabel, Joshua D. Bocarsly, Ram Seshadri, and Leopoldo Molina-Luna
- Subjects
Materials science ,Magnetism ,Annealing (metallurgy) ,General Chemical Engineering ,Analytical chemistry ,Nanoparticle ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Crystallography ,Iron nitride ,chemistry.chemical_compound ,Ferromagnetism ,chemistry ,Transmission electron microscopy ,Materials Chemistry ,Curie temperature ,Partial oxidation ,0210 nano-technology - Abstract
e-Fe3N shows interesting magnetism but is difficult to obtain as a pure and single-phase sample. We report a new preparation method using the reduction of iron(II) bromide with elemental sodium in liquid ammonia at −78 °C, followed by annealing at 573 K. Nanostructured and monophasic oxygen-free iron nitride, e-Fe3N, is produced according to X-ray diffraction and transmission electron microscopy experiments. The magnetic properties between 2 and 625 K were characterized using a vibrating sample magnetometer, revealing soft ferromagnetic behavior with a low-temperature average moment of 1.5 μB/Fe and a Curie temperature of 500 K. TC is lower than that of bulk e-Fe3N (575 K) [Chem. Phys. Lett 2010, 493, 299], which corresponds well with the small particle size within the agglomerates (15.4 (±4.1) nm according to TEM, 15.8(1) according to XRD). Samples were analyzed before and after partial oxidation (Fe3N–FexOy core–shell nanoparticles with a 2–3 nm thick shell) by X-ray diffraction, transmission electron m...
- Published
- 2017
27. Study of the Coarsening of Nanoporous Gold Nanowires by In Situ Scanning Transmission Electron Microscopy During Annealing
- Author
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Abdel-Aziz El Mel, Junjun Ding, Leopoldo Molina-Luna, Pierre-Yves Tessier, Adrien Chauvin, Chang-Hwan Choi, Charles University [Prague] (CU), Department of Material- and Geosciences, Darmstadt, Technische Universität Darmstadt (TU Darmstadt), Alfred University, Stevens Institute of Technology [Hoboken], Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), and Université de Nantes (UN)-Université de Nantes (UN)
- Subjects
In situ ,Materials science ,Nanoporous ,Annealing (metallurgy) ,Nanowire ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Scanning transmission electron microscopy ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,General Materials Science ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2019
28. Highly Accurate Analytic Modeling of Dispersive Field Distributions in MIM Capacitances With Electrodes Thinner Than Skin Depth
- Author
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Patrick Salg, Daniel Kienemund, Lukas Zeinar, Lambert Alff, Aldin Radetinac, Philipp Komissinskiy, Rolf Jakoby, Holger Maune, Dominik Walk, and Leopoldo Molina-Luna
- Subjects
Radiation ,Materials science ,Mean squared error ,Impedance matching ,Schematic ,020206 networking & telecommunications ,02 engineering and technology ,Dielectric ,Condensed Matter Physics ,Capacitance ,law.invention ,Computational physics ,Characterization (materials science) ,Capacitor ,law ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Electrical impedance - Abstract
Rapid dielectric characterization and modeling play an essential role in developing new technologies and materials for RF systems. In RF frontends, flexible impedance matching and frequency tuning can be introduced by deploying tunable capacitors (varactors), e.g., in metal-insulator–metal (MIM) configuration. On the physical side, test structures are available that only require patterning of the top layer and allow a fast characterization. On the modeling side, still, time-consuming 3-D EM simulations are necessary to extract the corresponding material properties. While analytic/schematic modeling would be fast, no accurate models that closely fit the dispersive characteristic are available up to now. In this article, we present a novel analytic model derived from the common $RLC$ model, which splits the electrode’s contribution into two parts and adds a parallel substrate impedance. Other than the common $RLC$ model, it is consistent for varying thickness of the dielectric and electrode, electrode conductivity, and dielectric properties. This model is verified by systematic, multivariate simulations and a large set of measured test structures. The analysis shows that the root mean squared error (RMSE) can be decreased by orders with our model.
- Published
- 2019
- Full Text
- View/download PDF
29. Analysis and simulation of the multiple resistive switching modes occurring in HfO x -based resistive random access memories using memdiodes
- Author
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Robert Eilhardt, Nico Kaiser, S. U. Sharath, Enrique Miranda, Lambert Alff, J. Muñoz-Gorriz, Eszter Piros, Stefan Petzold, Alexander Zintler, Tobias Vogel, Jordi Suñé, and Leopoldo Molina-Luna
- Subjects
Metal insulator metals ,Materials science ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,Stack (abstract data type) ,0103 physical sciences ,Resistive switching ,Analysis and simulation ,Polarity (mutual inductance) ,Diode ,Switching phenomenon ,010302 applied physics ,Resistive touchscreen ,business.industry ,Oxygen stoichiometry ,Process (computing) ,Electrical conduction ,021001 nanoscience & nanotechnology ,Thermal conduction ,Interface engineering ,Resistive random access memory ,Optoelectronics ,0210 nano-technology ,business ,Random access ,Voltage - Abstract
In this work, analysis and simulation of all experimentally observed switching modes in hafnium oxide based resistive random access memories are carried out using a simplified electrical conduction model. To achieve switching mode variation, two metal-insulator-metal cells with identical stack combination, but varying oxygen stoichiometry of the hafnia layer, namely, stoichiometric vs highly deficient, are considered. To access the individual switching modes, the devices were subjected to a variety of cycling conditions comprising different voltage and current ranges. For modeling the device behavior, a single or two antiserially connected memdiodes (diode with memory) were utilized. In this way, successful compact simulation of unipolar, bipolar, threshold, and complementary resistive switching modes is accomplished confirming the coexistence of two switching mechanisms of opposite polarity as the basis for all observable switching phenomena in this material. We show that only calibration of the outer current-voltage loops with the memdiode model is necessary for predicting the device behavior in the defined region revealing additional information on the switching process. The correspondence of each memdiode device with the conduction characteristics of the individual top and bottom metal-oxide contacts allows one to assess the role played by each interface in the switching process separately. This identification paves the path for a future improvement of the device performance and functionality by means of appropriate interface engineering.
- Published
- 2019
- Full Text
- View/download PDF
30. Forming‐Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices
- Author
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Eszter Piros, Lambert Alff, Nico Kaiser, S. U. Sharath, Keith P. McKenna, Alexander Zintler, Tobias Vogel, Marton Major, Leopoldo Molina-Luna, Robert Eilhardt, and Stefan Petzold
- Subjects
010302 applied physics ,Materials science ,business.industry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Resistive random-access memory ,Hafnium oxide ,Texture transfer ,Transmission electron microscopy ,0103 physical sciences ,Optoelectronics ,Grain boundary ,Resistive switching memory ,0210 nano-technology ,business - Published
- 2019
- Full Text
- View/download PDF
31. Towards a Greener and Scalable Synthesis of Na 2 Ti 6 O 13 Nanorods and Their Application as Anodes in Batteries for Grid‐Level Energy Storage
- Author
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Leopoldo Molina-Luna, Samira A. Kiefer, Dragoljub Vrankovic, Ralf Riedel, Magdalena Graczyk-Zajac, Michael Dürrschnabel, Enrico Bruder, and Dario M. De Carolis
- Subjects
Materials science ,molten salt synthesis ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,Electrochemistry ,7. Clean energy ,01 natural sciences ,Energy storage ,anode materials ,Graphite ,Molten salt ,sodium ,Engineering & allied operations ,Full Paper ,Full Papers ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Anode ,General Energy ,chemistry ,Chemical engineering ,lithium ,Lithium ,Grid energy storage ,Nanorod ,ddc:620 ,0210 nano-technology ,grid storage - Abstract
Grid applications require high power density (for frequency regulation, load leveling, and renewable energy integration), achievable by combining multiple batteries in a system without strict high capacity requirements. For these applications however, safety, cost efficiency, and the lifespan of electrode materials are crucial. Titanates, safe and longevous anode materials providing much lower energy density than graphite, are excellent candidates for this application. The innovative molten salt synthesis approach proposed in this work provides exceptionally pure Na2Ti6O13 nanorods generated at 900–1100 °C in a yield ≥80 wt%. It is fast, cost‐efficient, and suitable for industrial upscaling. Electrochemical tests reveal stable performance providing capacities of ≈100 mA h g−1 (Li) and 40 mA h g−1 (Na). Increasing the synthesis temperature to 1100 °C leads to a capacity decrease, most likely resulting from 1) the morphology/volume change with the synthesis temperature and 2) distortion of the Na2Ti6O13 tunnel structure indicated by electron energy‐loss and Raman spectroscopy. The suitability of pristine Na2Ti6O13 as the anode for grid‐level energy storage systems has been proven a priori, without any performance‐boosting treatment, indicating considerable application potential especially due to the high yield and low cost of the synthesis route., Highly pure Na2Ti6O13 is reliably obtained via molten salt synthesis (MSS). Its suitability as an anode for Li‐ion and Na‐ion batteries has been proven a priori, without any performance‐boosting treatment (e.g., carbon coating and activation process), indicating considerable application potential, especially for grid‐scale energy storage devices. MSS has also proven to be suitable for industrial upscaling.© 2020 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
- Published
- 2020
32. Microstructure and magnetic properties of melt-spun Alnico-5 alloys
- Author
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Konrad Löwe, Leopoldo Molina-Luna, Michael Dürrschnabel, Bianca Frincu, Hans-Joachim Kleebe, Rajasekhar Madugundo, Oliver Gutfleisch, and George C. Hadjipanayis
- Subjects
010302 applied physics ,Spinodal ,Materials science ,Annealing (metallurgy) ,Spinodal decomposition ,Alnico ,02 engineering and technology ,engineering.material ,Coercivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Grain size ,Electronic, Optical and Magnetic Materials ,Nuclear magnetic resonance ,0103 physical sciences ,engineering ,Melt spinning ,Composite material ,0210 nano-technology - Abstract
The aim of this work is to investigate the effect of very fine grain sizes on the spinodal decomposition in the Alnico system. Commercial Alnico 5 was melted and melt-spun with varying copper wheel speeds, which led to a grain size of 1–2 µm. This value was further reduced to sub-micrometer size by a small addition of Boron (1 at%). The spinodal decomposition was induced through a two-step annealing treatment under magnetic field in the range of 600–900 °C. It was found that the size of the spinodal structures is not influenced much by increased wheel speeds but becomes smaller with the addition of Boron. However, the difference in coercivity between the samples with and without Boron is only 50 Oe (4 kA/m). To study the influence of the annealing treatment two sets of samples are compared, one with the highest coercivity (366 Oe/29 kA/m) and the other one with lower coercivity (180 Oe/14.5 kA/m). We found with Scanning transmission electron microscopy Energy-dispersive X-ray spectroscopy (STEM EDX) a much sharper chemical interface between the α1 and α2 precipitates in the former sample, which we attribute to be the main reason for the higher coercivity.
- Published
- 2016
33. Electroless decoration of macroscale foam with nickel nano-spikes: A scalable route toward efficient catalyst electrodes
- Author
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Joachim Brötz, Shouxin Liu, Michael Duerrschnabel, Jia Tan, Wolfgang Ensinger, Hans-Joachim Kleebe, Sandra Schaefer, Xin Zhao, Leopoldo Molina-Luna, and Falk Muench
- Subjects
Materials science ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Catalysis ,lcsh:Chemistry ,Metal ,Nickel ,lcsh:Industrial electrochemistry ,lcsh:QD1-999 ,chemistry ,visual_art ,Mass transfer ,Nano ,Electrode ,Electrochemistry ,visual_art.visual_art_medium ,Sawdust ,0210 nano-technology ,Porosity ,lcsh:TP250-261 - Abstract
Electroless deposition of anisotropic catalyst layers is introduced as an efficient approach to fabricate high-performing multiscale electrode architectures. In the present study, a biomass-derived, solidified foam is coated with nickel nano-spikes. This results in an amplification of the surface area and an introduction of catalytic functionality, while the favorable mass transfer properties of the porous support are retained. Both the substrate and the metal film are produced using simple, readily scalable processes. The support is prepared from liquefied sawdust by self-foaming, and nickel deposition is performed by immersion in a hydrazine-based plating bath. The favorable functional properties of the nickel-coated foam are demonstrated in enzyme-free glucose sensing. Due to the large surface area and the high activity of the nickel nanofilm, an outstanding sensitivity of 8.1 mA mM−1 cm−2 and a low detection limit of 60 nM were achieved. Keywords: Anisotropic nanoparticles, Electrode nanostructuring, Electroless plating, Biomass conversion, Enzyme-free glucose sensing
- Published
- 2016
34. Formation of the core–shell microstructure in lead-free Bi1/2Na1/2TiO3-SrTiO3 piezoceramics and its influence on the electromechanical properties
- Author
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Leopoldo Molina-Luna, Virginia Rojas, Hans-Joachim Kleebe, Ulrike Kunz, Michael Duerrschnabel, Matias Acosta, and Jurij Koruza
- Subjects
010302 applied physics ,Phase transition ,Thermogravimetric analysis ,Materials science ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Piezoelectricity ,law.invention ,law ,Transmission electron microscopy ,Metastability ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Calcination ,Ceramic ,Composite material ,0210 nano-technology - Abstract
The Bi1/2Na1/2TiO3-based materials exhibit the largest electric-field-induced strains among lead-free piezoceramics and are considered as promising candidates for actuation applications. A typical representative of this group is (1-x)Bi1/2Na1/2TiO3-xSrTiO3, where its excellent electromechanical properties were recently related to the existence of a core–shell microstructure. Although the latter was also reported in other Bi1/2Na1/2TiO3-based ceramics, the formation mechanism remains unknown. In the present work we therefore first investigated the solid-state reaction occurring during calcination using simultaneous thermogravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy. The reaction occurred in two steps, whereby the cores and shells had different formation reaction temperatures, which resulted in a metastable heterogeneous microstructure. Furthermore, a series of sintered samples with different relative densities, grain sizes, and core densities was prepared. Modifications of these microstructural parameters resulted in variation of the maximal strain by 17% and in the electric-field required to trigger the phase transitions by 38%.
- Published
- 2016
35. Tailoring the Switching Dynamics in Yttrium Oxide‐Based RRAM Devices by Oxygen Engineering: From Digital to Multi‐Level Quantization toward Analog Switching
- Author
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Eszter Piros, Eric Jalaguier, Christelle Charpin-Nicolle, Leopoldo Molina-Luna, Aldin Radetinac, Emmanuel Nolot, Tobias Vogel, Stefan Petzold, Enrique Miranda, Philipp Komissinskiy, Nico Kaiser, Alexander Zintler, Lambert Alff, Robert Eilhardt, and Christian Wenger
- Subjects
010302 applied physics ,Mesoscopic physics ,Resistive touchscreen ,Materials science ,business.industry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Resistive random-access memory ,Quantization (physics) ,Thermal conductivity ,Neuromorphic engineering ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Voltage - Abstract
This work investigates the transition from digital to gradual or analog resistive switching in yttrium oxide-based resistive random-access memory devices. It is shown that this transition is determined by the amount of oxygen in the functional layer. A homogeneous reduction of the oxygen content not only reduces the electroforming voltage, allowing for forming-free devices, but also decreases the voltage operation window of switching, thereby reducing intra-device variability. The most important effect as the dielectric becomes substoichiometric by oxygen engineering is that more intermediate (quantized) conduction states are accessible. A key factor for this reproducibly controllable behavior is the reduced local heat dissipation in the filament region due to the increased thermal conductivity of the oxygen depleted layer. The improved accessibility of quantized resistance states results in a semi-gradual switching both for the set and reset processes, as strongly desired for multi-bit storage and for an accurate definition of the synaptic weights in neuromorphic systems. A theoretical model based on the physics of mesoscopic structures describing current transport through a nano-constriction including asymmetric potential drops at the electrodes and non-linear conductance quantization is provided. The results contribute to a deeper understanding on how to tailor materials properties for novel memristive functionalities.
- Published
- 2020
36. Temperature-dependent evolution of crystallographic and domain structures in (K, Na, Li)(Ta, Nb)O3 piezoelectric single crystals
- Author
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Leopoldo Molina-Luna, Alexander Zintler, Daniel Rytz, Hairui Liu, Philippe Veber, Jurij Koruza, Mario Maglione, Department of Materials and Earth Sciences [Darmstadt], Technische Universität Darmstadt (TU Darmstadt), Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut Lumière Matière [Villeurbanne] (ILM), Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon, FEE, and FEE GmBh
- Subjects
010302 applied physics ,Materials science ,Acoustics and Ultrasonics ,02 engineering and technology ,Crystal structure ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Crystal ,Condensed Matter::Materials Science ,Tetragonal crystal system ,Crystallography ,0103 physical sciences ,Curie temperature ,Orthorhombic crystal system ,Electrical and Electronic Engineering ,0210 nano-technology ,Instrumentation ,Single crystal - Abstract
International audience; (K,Na)NbO 3 -based ferroelectric single crystals have recently undergone a substantial development, resulting in improved crystal quality and large piezoelectric coefficients, exceeding 700 pC/N, over a broad temperature range. However, further development necessitates a detailed understanding of the mechanisms defining the domain structure and its temperature evolution. This paper presents the investigation into the crystallographic structure and domain configurations of a (K,Na,Li)(Ta,Nb)O 3 single crystal over a broad temperature range. The crystal was grown by the submerged-seed solution growth technique and investigated using in situ transmission electron microscopy, X-ray diffraction, dielectric measurements, and polarized light microscopy. The lattice distortion, structural phase transitions, and domain configurations are reported. A transition from the lamellar orthorhombic to the rectangular tetragonal domain structure is observed upon heating. Moreover, the milky optical appearance of the crystal was investigated and found to result from the presence of regions with different domain configurations and domain sizes. The formation of these regions is related to the growth defects, which govern the domain formation when cooling below the Curie temperature.
- Published
- 2018
37. Template-Free Electroless Plating of Gold Nanowires: Direct Surface Functionalization with Shape-Selective Nanostructures for Electrochemical Applications
- Author
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Alexander Vaskevich, Wolfgang Ensinger, Hans-Joachim Kleebe, Joachim Brötz, Sandra Schaefer, Falk Muench, Lorenz Hagelüken, Michael Duerrschnabel, Israel Rubinstein, and Leopoldo Molina-Luna
- Subjects
Nanostructure ,Materials science ,Nanowire ,Nucleation ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Nanomaterials ,Template ,Plating ,Surface modification ,General Materials Science ,0210 nano-technology - Abstract
Metal nanowires (NWs) represent a prominent nanomaterial class, the interest in which is fueled by their tunable properties as well as their excellent performance in, for example, sensing, catalysis, and plasmonics. Synthetic approaches to obtain metal NWs mostly produce colloids or rely on templates. Integrating such nanowires into devices necessitates additional fabrication steps, such as template removal, nanostructure purification, or attachment. Here, we describe the development of a facile electroless plating protocol for the direct deposition of gold nanowire films, requiring neither templates nor complex instrumentation. The method is general, producing three-dimensional nanowire structures on substrates of varying shape and composition, with different seed types. The aqueous plating bath is prepared by ligand exchange and partial reduction of tetrachloroauric acid in the presence of 4-dimethylaminopyridine and formaldehyde. Gold deposition proceeds by nucleation of new grains on existing nanostructure tips and thus selectively produces curvy, polycrystalline nanowires of high aspect ratio. The nanofabrication potential of this method is demonstrated by producing a sensor electrode, whose performance is comparable to that of known nanostructures and discussed in terms of the catalyst architecture. Due to its flexibility and simplicity, shape-selective electroless plating is a promising new tool for functionalizing surfaces with anisotropic metal nanostructures.
- Published
- 2017
38. MEMS-based sample carriers for simultaneous heating and biasing experiments: A platform for in-situ TEM analysis
- Author
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Leopoldo Molina Luna, Ronald G. Spruit, Qiang Xu, Merijn Pen, Mariya Sholkina, Yevheniy Pivak, Hector Hugo Perez Garza, and J. Tijn van Omme
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010302 applied physics ,Microelectromechanical systems ,Microheater ,Materials science ,business.industry ,Electrical engineering ,Biasing ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Characterization (materials science) ,Transmission electron microscopy ,Electric field ,0103 physical sciences ,Cathode ray ,Optoelectronics ,0210 nano-technology ,business - Abstract
We present the development of a MEMS-based sample carrier to be used for in-situ studies inside the Transmission Electron Microscope (TEM). This MEMS device, referred to as the Nano-Chip, acts as a multifunctional sample carrier and micro-sized laboratory for simultaneous heating and biasing experiments. Each Nano-Chip consists of eight contacts, which enable four-point-probe measurements for both heating and biasing purposes. The microheater enables temperatures up to 800°C. Similarly, the system allows to apply up to 100V, which can result in electric fields as high as 200kV/cm. Samples are placed directly onto the electron transparent windows which allow for the electron beam to pass through for in-situ imaging. This system represents a cost-effective add-on to the TEM, which acts as the ideal tool for failure analysis of semiconductor materials, characterization of batteries, fuel cells and studies of structure responses to electric fields.
- Published
- 2017
39. Synthesis, morphology, thermal stability and magnetic properties of α″-Fe16N2 nanoparticles obtained by hydrogen reduction of γ-Fe2O3 and subsequent nitrogenation
- Author
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I. Dirba, Philipp Komissinskiy, Leopoldo Molina-Luna, Hans-Joachim Kleebe, C. A. Schwöbel, Michael Duerrschnabel, L.V.B. Diop, Kathrin Hofmann, Oliver Gutfleisch, and Technische Universität Darmstadt (TU Darmstadt)
- Subjects
Materials science ,Polymers and Plastics ,Hydrogen ,Nanoparticle ,chemistry.chemical_element ,02 engineering and technology ,7. Clean energy ,01 natural sciences ,Ammonia ,chemistry.chemical_compound ,Nuclear magnetic resonance ,0103 physical sciences ,Thermal stability ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Chemical composition ,ComputingMilieux_MISCELLANEOUS ,010302 applied physics ,[PHYS]Physics [physics] ,Metals and Alloys ,[CHIM.MATE]Chemical Sciences/Material chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,Electronic, Optical and Magnetic Materials ,Chemical engineering ,chemistry ,Ceramics and Composites ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Particle ,Particle size ,0210 nano-technology - Abstract
Typical synthesis of α″-Fe16N2 nanoparticles involves reduction of iron oxides by hydrogen at elevated temperatures which is disadvantageous due to the particle coalescence. Here we report on a process for reduction of iron oxides at elevated pressures and show that by increasing hydrogen pressure from atmospheric to 53 MPa, it is possible to reduce the reaction temperature from 663 K down to 483 K, resulting in phase-pure α-Fe nanoparticles without noticeable particle growth. By subsequent nitrogenation in an ammonia flow, fine, 99% phase-pure α″-Fe16N2 nanoparticles could be synthesized. The reduction temperature and the respective particle size has a significant influence on the nitrogenation step. α″-Fe16N2 nanoparticles exhibit semi-hard magnetic properties with Ms(0) = 215 Am2 kg−1, μ0Hc = 0.22 T, TC = 634 K and exchange stiffness Ac = 6.84 pJ m−1, Aa,b = 7.53 pJ m−1. Synthesis conditions, microstructure, chemical composition and thermal stability of the nanoparticles are systematically studied and correlated with the observed magnetic properties.
- Published
- 2017
40. Zn based nanoparticle–carbon nanotube hybrid materials: Interaction and charge transfer
- Author
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Hans-Joachim Kleebe, Abdel-Aziz El Mel, Marie Buffiere, Leopoldo Molina-Luna, Carla Bittencourt, Christopher P. Ewels, Rony Snyders, Jean-François Colomer, Eric Faulques, Stephanos Konstantinidis, Chimie des Interactions Plasma-Surface (ChIPS) (ChIPS), Université de Mons-Hainaut, Department of Electrical Engineering [KU Leuven] (KU-ESAT), Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), IMEC (IMEC), Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Department of Material- and Geosciences, Darmstadt, Technische Universität Darmstadt (TU Darmstadt), Laboratoire de Résonance Magnétique Nucléaire (LRMN), Facultés Universitaires Notre Dame de la Paix (FUNDP), Materia Nova Research Center (MNRC), and Materia Nova Research Center
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Thermal oxidation ,Photoluminescence ,Materials science ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Carbon nanotube ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Metal ,X-ray photoelectron spectroscopy ,Chemical engineering ,law ,visual_art ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,visual_art.visual_art_medium ,General Materials Science ,0210 nano-technology ,Hybrid material ,Spectroscopy - Abstract
International audience; The interaction and charge transfer between Zn-based nanoparticles (NPs) and carbon nanotubes (CNTs) is investigated by X-ray Auger and photoelectron spectroscopy. Charge transfer from Zn NPs toward the CNTs is demonstrated by the presence of an additional feature revealed in the C 1s spectrum of CNTs. This charge transfer was found to vanish after thermal oxidation due to the transformation of the metal Zn into ZnO. Photoluminescence (PL) spectroscopy shows that in the samples ZnO(Nps)/CNTs the PL intensity is quenched. (C) 2013 Elsevier Ltd. All rights reserved.
- Published
- 2014
41. Free-Standing Networks of Core-Shell Metal and Metal Oxide Nanotubes for Glucose Sensing
- Author
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Hans-Joachim Kleebe, Wolfgang Ensinger, Tintula Kottakkat, Markus Antoni, Sandra Schaefer, Leopoldo Molina-Luna, Luwan Sun, Michael Duerrschnabel, Christina Roth, Falk Muench, Sevda Ayata, and Ulrike Kunz
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Thermal oxidation ,Nanotube ,Materials science ,Ion track ,Oxide ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Nanomaterials ,Electroless nickel ,chemistry.chemical_compound ,chemistry ,Copper plating ,General Materials Science ,0210 nano-technology ,Bimetallic strip - Abstract
Nanotube assemblies represent an emerging class of advanced functional materials, whose utility is however hampered by intricate production processes. In this work, three classes of nanotube networks (monometallic, bimetallic, and metal oxide) are synthesized solely using facile redox reactions and Commercially available ion track membranes. First,, the disordered pores of an ion track membrane are widened by chemical etching; resulting in the formation of a strongly interconnected pore network. Replicating this template structure with electroless copper plating yields a monolithic film composed, of crossing metal nanotubes. We show that the parent material can be easily transformed into bimetallic or oxidic derivatives by applying a second electroless plating or thermal oxidation step. These treatments retain the monolithic network structure but result in the formation of core shell nanotubes of altered composition (thermal oxidation: Cu2O-CuO); electroless nickel coating: Cu-Ni). The obtained nanomaterials are applied in the enzyme-free electrochemical detection of glucose, showing very high sensitivities between 2.27 and 2.83 A M-1 cm(-2). Depending on the-material composition, varying reactivities were observed: While copper oxidation reduces the response to glucose, it is increased in the case of nickel modification, albeit at the cost of decreased. selectivity. The performance of the materials is explained by the network architecture, which combines the advantages of one-dimensional nano-objects (continuous, conduction pathways, high surface area) with those of a self-supporting, open-porous superstructure (binder-free catalyst layer, efficient diffusion). In summary, this novel synthetic approach provides a fast, scalable, and flexible route toward free-standing nanotube arrays of high compositional complexity.
- Published
- 2016
42. Atomically interface engineered micrometer-thick SrMoO3 oxide electrodes for thin-film BaxSr1-xTiO3 ferroelectric varactors tunable at low voltages
- Author
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Lambert Alff, Leopoldo Molina-Luna, Holger Maune, Patrick Salg, Dominik Walk, Aldin Radetinac, Alexander Zintler, Philipp Komissinskiy, Rolf Jakoby, and Lukas Zeinar
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Materials science ,lcsh:Biotechnology ,Oxide ,02 engineering and technology ,Substrate (electronics) ,01 natural sciences ,law.invention ,Pulsed laser deposition ,Micrometre ,chemistry.chemical_compound ,law ,lcsh:TP248.13-248.65 ,0103 physical sciences ,General Materials Science ,Thin film ,010302 applied physics ,business.industry ,General Engineering ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,Capacitor ,chemistry ,Electrode ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) ,lcsh:Physics - Abstract
In the field of oxide electronics, there has been tremendous progress in the recent years in atomic engineering of functional oxide thin films with controlled interfaces at the unit cell level. However, some relevant devices such as tunable ferroelectric microwave capacitors (varactors) based on BaxSr1−xTiO3 are stymied by the absence of suited compatible, very low resistive oxide electrode materials on the micrometer scale. Therefore, we start with the epitaxial growth of the exceptionally highly conducting isostructural perovskite SrMoO3 having a higher room-temperature conductivity than Pt. In high-frequency applications such as tunable filters and antennas, the desired electrode thickness is determined by the electromagnetic skin depth, which is of the order of several micrometers in the frequency range of a few gigahertz. Here, we report the pulsed laser deposition of a fully layer-by-layer grown epitaxial device stack, combining a several micrometers thick electrode of SrMoO3 with atomically engineered sharp interfaces to the substrate and to the subsequently grown functional dielectric layer. The difficult to achieve epitaxial thick film growth makes use of the extraordinary ability of perovskites to accommodate strain well beyond the critical thickness limit by adjusting their lattice constant with small shifts in the cation ratio, tuned by deposition parameters. We show that our approach, encompassing several orders of magnitude in film thickness scale whilst maintaining atomic layer control, enables the fabrication of metal-insulator-metal (MIM) varactors based on 50–100 nm thin BaxSr1−xTiO3 layers with high tunability above three at the Li-ion battery voltage level (3.7 V).
- Published
- 2019
43. Controlling the Formation of Nanocavities in Kirkendall Nanoobjects through Sequential Thermal Ex Situ Oxidation and In Situ Reduction Reactions
- Author
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Rony Snyders, Eric Gautron, Abdel-Aziz El Mel, Carla Bittencourt, Stephanos Konstantinidis, Ke Du, Pierre-Yves Tessier, Leopoldo Molina-Luna, Chang-Hwan Choi, Marie Buffiere, Junjun Ding, Institut des Matériaux Jean Rouxel (IMN), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), IMEC (IMEC), Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), Stevens Institute of Technology [Hoboken], Chimie des Interactions Plasma-Surface (ChIPS) (ChIPS), Université de Mons-Hainaut, LCIA (LCIA), Department of Material- and Geosciences, Darmstadt, and Technische Universität Darmstadt (TU Darmstadt)
- Subjects
Nanotube ,Nanostructure ,Materials science ,Kirkendall effect ,Oxide ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,0104 chemical sciences ,Nanomaterials ,Biomaterials ,chemistry.chemical_compound ,chemistry ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,General Materials Science ,Nanorod ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS ,Biotechnology - Abstract
Controlling the porosity, the shape, and the morphology of Kirkendall hollow nanostructures is the key factor to tune the properties of these tailor-made nanomaterials which allow in turn broadening their applications. It is shown that by applying a continuous oxidation to copper nanowires following a temperature ramp protocol, one can synthesize cuprous oxide nanotubes containing periodic copper nanoparticles. A further oxidation of such nanoobjects allows obtaining cupric oxide nanotubes with a bamboo-like structure. On the other hand, by applying a sequential oxidation and reduction reactions to copper nanowires, one can synthesize hollow nanoobjects with complex shapes and morphologies that cannot be obtained using the Kirkendall effect alone, such as necklace-like cuprous oxide nanotubes, periodic solid copper nanoparticles or hollow cuprous oxide nanospheres interconnected with single crystal cuprous oxide nanorods, and aligned and periodic hollow nanospheres embedded in a cuprous oxide nanotube. The strategy demonstrated in this study opens new avenues for the engineering of hollow nanostructures with potential applications in gas sensing, catalysis, and energy storage.
- Published
- 2016
44. Planar Arrays of Nanoporous Gold Nanowires: When Electrochemical Dealloying Meets Nanopatterning
- Author
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Ke Du, P. Y. Tessier, Cyril Delacôte, Damien Thiry, Chang-Hwan Choi, Michael Duerrschnabel, Leopoldo Molina-Luna, Junjun Ding, Adrien Chauvin, Abdel-Aziz El Mel, Mohammed Boujtita, École nationale supérieure d'architecture de Nantes (ENSA Nantes), Chimie Et Interdisciplinarité : Synthèse, Analyse, Modélisation (CEISAM), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), Department of Material- and Geosciences, Darmstadt, Technische Universität Darmstadt (TU Darmstadt), Chimie des Interactions Plasma-Surface (ChIPS) (ChIPS), Université de Mons-Hainaut, Stevens Institute of Technology [Hoboken], Institut des Matériaux Jean Rouxel (IMN), Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Ecole Polytechnique de l'Université de Nantes (EPUN), Université de Nantes (UN)-Université de Nantes (UN), Laboratoire de Chimie des interactions plasma surface (CHIPS), and Université de Mons (UMons)
- Subjects
Nanostructure ,Materials science ,Silicon ,Nanoporous ,Nanowires ,Nanowire ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Substrate (electronics) ,Electrochemical Techniques ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry ,Macroscopic scale ,Cavity magnetron ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,General Materials Science ,Gold ,0210 nano-technology ,Porosity ,ComputingMilieux_MISCELLANEOUS - Abstract
Nanoporous materials are of great interest for various technological applications including sensors based on surface-enhanced Raman scattering, catalysis, and biotechnology. Currently, tremendous efforts are dedicated to the development of porous one-dimensional materials to improve the properties of such class of materials. The main drawback of the synthesis approaches reported so far includes (i) the short length of the porous nanowires, which cannot reach the macroscopic scale, and (ii) the poor organization of the nanostructures obtained by the end of the synthesis process. In this work, we report for the first time on a two-step approach allowing creating highly ordered porous gold nanowire arrays with a length up to a few centimeters. This two-step approach consists of the growth of gold/copper alloy nanowires by magnetron cosputtering on a nanograted silicon substrate, serving as a physical template, followed by a selective dissolution of copper by an electrochemical anodic process in diluted sulfuric acid. We demonstrate that the pore size of the nanowires can be tailored between 6 and 21 nm by tuning the dealloying voltage between 0.2 and 0.4 V and the dealloying time within the range of 150-600 s. We further show that the initial gold content (11 to 26 atom %) and the diameter of the gold/copper alloy nanowires (135 to 250 nm) are two important parameters that must carefully be selected to precisely control the porosity of the material.
- Published
- 2016
45. Control of Switching Modes and Conductance Quantization in Oxygen Engineered HfOxbased Memristive Devices
- Author
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Hans-Joachim Kleebe, Gang Niu, Michael Lehmann, T. Niermann, Erwin Hildebrandt, Michael Duerrschnabel, Lambert Alff, Thomas Schroeder, P. Calka, S. U. Sharath, Stefan Vogel, Christian Wenger, Leopoldo Molina-Luna, and Jose Kurian
- Subjects
010302 applied physics ,Materials science ,business.industry ,Quantization (signal processing) ,Conductance ,Nanotechnology ,02 engineering and technology ,Memristor ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Resistive random-access memory ,law.invention ,Biomaterials ,Neuromorphic engineering ,law ,0103 physical sciences ,Electrochemistry ,Optoelectronics ,0210 nano-technology ,Joule heating ,business ,Quantum - Abstract
Hafnium oxide (HfOx)-based memristive devices have tremendous potential as nonvolatile resistive random access memory (RRAM) and in neuromorphic electronics. Despite its seemingly simple two-terminal structure, a myriad of RRAM devices reported in the rapidly growing literature exhibit rather complex resistive switching behaviors. Using Pt/HfOx/TiN-based metal–insulator–metal structures as model systems, it is shown that a well-controlled oxygen stoichiometry governs the filament formation and the occurrence of multiple switching modes. The oxygen vacancy concentration is found to be the key factor in manipulating the balance between electric field and Joule heating during formation, rupture (reset), and reformation (set) of the conductive filaments in the dielectric. In addition, the engineering of oxygen vacancies stabilizes atomic size filament constrictions exhibiting integer and half-integer conductance quantization at room temperature during set and reset. Identifying the materials conditions of different switching modes and conductance quantization contributes to a unified switching model correlating structural and functional properties of RRAM materials. The possibility to engineer the oxygen stoichiometry in HfOx will allow creating quantum point contacts with multiple conductance quanta as a first step toward multilevel memristive quantum devices.
- Published
- 2017
46. Electrochemical Li Storage Properties of Carbon-Rich B–C–N Ceramics
- Author
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Shrikant Bhat, Pradeep Vallachira Warriam Sasikumar, Leopoldo Molina-Luna, Hans-Joachim Kleebe, Magdalena Graczyk-Zajac, and Ralf Riedel
- Subjects
Materials science ,chemistry.chemical_element ,02 engineering and technology ,General Medicine ,BCN ceramics ,Li-ion batteries ,rate capability ,cycling stability ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Amorphous solid ,symbols.namesake ,chemistry ,Transmission electron microscopy ,visual_art ,visual_art.visual_art_medium ,symbols ,Lithium ,Crystallite ,Ceramic ,0210 nano-technology ,Raman spectroscopy ,Carbon ,Nuclear chemistry - Abstract
Amorphous BCN ceramics were synthesized via a thermal conversion procedure of piperazine���borane and pyridine���borane. The synthesized BC���N and BC���N ceramics contained, in their final amorphous structure, 45 and 65 wt % of carbon, respectively. Elemental analysis revealed 45 and 65 wt % of carbon for BC���N and BC���N, respectively. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the amorphous nature of studied compounds. Lateral cluster size of carbon crystallites of 7.43 and 10.3 nm for BC���N and BC���N, respectively, was calculated from Raman spectroscopy data. This signified a higher order of the carbon phase present in BC���N. The electrochemical investigation of the low carbon BC���N composition as anodes for Li-ion batteries revealed initial capacities of 667 and 235 mAh��g����� for lithium insertion/extraction, respectively. The material with higher carbon content, BC���N, disclosed better reversible lithium storage properties. Initial capacities of 1030 and 737 mAh��g����� for lithium insertion and extraction were recovered for carbon-rich BC���N composition. Extended cycling with high currents up to 2 C/2 D revealed the cycling stability of BC4N electrodes. Cycling for more than 75 cycles at constant current rates showed a stable electrochemical behavior of BC���N anodes with capacities as high as 500 mAh��g�����.
- Published
- 2016
47. Interlayer structure in YBCO-coated conductors prepared by chemical solution deposition
- Author
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Oliver Eibl, Bernhard Holzapfel, Thomas Thersleff, Stuart Turner, Leopoldo Molina-Luna, Jo Verbeeck, Ricardo Egoavil, and Gustaaf Van Tendeloo
- Subjects
Materials science ,Annealing (metallurgy) ,Physics ,Non-blocking I/O ,Metals and Alloys ,Thermal contact ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electron spectroscopy ,Transmission electron microscopy ,0103 physical sciences ,Scanning transmission electron microscopy ,Materials Chemistry ,Ceramics and Composites ,Electrical and Electronic Engineering ,Composite material ,Electric current ,010306 general physics ,0210 nano-technology ,Electrical conductor - Abstract
The functionality of YBa2Cu3O7 (YBCO)-coated conductor technology depends on the reliability and microstructural properties of a given tape or wire architecture. Particularly, the interface to the metal tape is of interest since it determines the adhesion, mechanical stability of the film and thermal contact of the film to the substrate. A trifluoroacetate (TFA)—metal organic deposition (MOD) prepared YBCO film deposited on a chemical solution-derived buffer layer architecture based on CeO2=La2Zr2O7 and grown on a flexible Ni5 at.%W substrate with af100gh001i biaxial texture was investigated. The YBCO film had a thickness was 440 nm and a jc of 1:02 MA cm 2 was determined at 77 K and zero external field. We present a sub-nanoscale analysis of a fully processed solution-derived YBCO-coated conductor by aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). For the first time, structural and chemical analysis of the valence has been carried out on the sub-nm scale. Intermixing of Ni, La, Ce, O and Ba takes place at these interfaces and gives rise to nanometer-sized interlayers which are a by-product of the sequential annealing process. Two distinct interfacial regions were analyzed in detail: (i) the YBCO=CeO2=La2Zr2O7 region (10 nm interlayer) and (ii) the La2Zr2O7=Ni‐5 at.%W substrate interface region (20 nm NiO). This is of particular significance for the functionality of these YBCO-coated conductor architectures grown by chemical solution deposition. (Some figures may appear in colour only in the online journal)
- Published
- 2013
48. Correlation of Structural Modifications by Multiscale Phase Mapping in Filamentary Type HfO 2 -based RRAM: Towards a Component Specific in situ TEM Investigation
- Author
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Alexander Zintler, Stefan Petzold, Robert Eilhardt, Leopoldo Molina-Luna, Nico Kaiser, Lambert Alff, and Sharath Ulhas
- Subjects
010302 applied physics ,In situ ,Materials science ,Chemical physics ,Component (UML) ,0103 physical sciences ,02 engineering and technology ,Phase mapping ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,Instrumentation ,Resistive random-access memory - Full Text
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49. Birth of a grain boundary: In situ TEM Observation of the Microstructure Evolution in HfO 2 Based Memristors
- Author
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Leopoldo Molina-Luna, Robert Eilhardt, Stefan Petzold, Alexander Zintler, Déspina Nasiou, Oscar Recalde, and Lambert Alff
- Subjects
010302 applied physics ,In situ ,Materials science ,02 engineering and technology ,Memristor ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Grain boundary ,Composite material ,0210 nano-technology ,Instrumentation - Full Text
- View/download PDF
50. Resistive Switching: Forming‐Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices (Adv. Electron. Mater. 10/2019)
- Author
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Lambert Alff, Robert Eilhardt, Eszter Piros, Leopoldo Molina-Luna, Keith P. McKenna, Nico Kaiser, S. U. Sharath, Tobias Vogel, Stefan Petzold, Alexander Zintler, and Marton Major
- Subjects
Materials science ,business.industry ,02 engineering and technology ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Hafnium oxide ,Resistive random-access memory ,Resistive switching ,Optoelectronics ,Grain boundary ,0210 nano-technology ,business - Full Text
- View/download PDF
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