TY - JOUR A1 - Gostkowska-Lekner, Natalia Katarzyna A1 - Wallacher, Dirk A1 - Grimm, Nico A1 - Habicht, Klaus A1 - Hofmann, Tommy T1 - A novel electrochemical anodization cell for the synthesis of mesoporous silicon JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - A novel design of an electrochemical anodization cell dedicated to the synthesis of mesoporous, single-crystalline silicon is presented. First and foremost, the design principle follows user safety since electrochemical etching of silicon requires highly hazardous electrolytes based on hydrofluoric (HF) acid. The novel cell design allows for safe electrolyte handling prior, during, and post-etching. A peristaltic pump with HF-resistant fluoroelastomer tubing transfers electrolytes between dedicated reservoirs and the anodization cell. Due to the flexibility of the cell operation, different processing conditions can be realized providing a large parameter range for the attainable sample thickness, its porosity, and the mean pore size. Rapid etching on the order of several minutes to synthesize micrometer-thick porous silicon epilayers on bulk silicon is possible as well as long-time etching with continuous, controlled electrolyte flow for several days to prepare up to 1000 mu m thick self-supporting porous silicon membranes. A highly adaptable, LabVIEW((TM))-based control software allows for user-defined etching profiles. Y1 - 2020 U6 - https://doi.org/10.1063/5.0008536 SN - 0034-6748 SN - 1089-7623 VL - 91 IS - 10 PB - American Institute of Physics CY - Melville, NY ER - TY - JOUR A1 - Kojda, Danny A1 - Hofmann, Tommy A1 - Gostkowska-Lekner, Natalia Katarzyna A1 - Habicht, Klaus T1 - Characterization and modeling of the temperature-dependent thermal conductivity in sintered porous silicon-aluminum nanomaterials JF - Nano research N2 - Nanostructured silicon and silicon-aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering (SPS) of silicon nanopowder, mesoporous silicon (pSi), and aluminum nanopowder. The interplay of metal-assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity. Morphology and temperature-dependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport. Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions. We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples. In contrast, strong grain growth is observed for sintered nanopowders under similar sintering conditions. We observe that aluminum agglomerations induce local grain growth, while aluminum diffusion is observed in porous silicon and dispersed nanoparticles. A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains. With a modified Landauer/Lundstrom approach the relative thermal conductivity and the scattering length are extracted. The relative thermal conductivity confirms the applicability of Kirkpatrick's effective medium theory. The extracted scattering lengths are in excellent agreement with the harmonic mean of log-normal distributed domain sizes and the interpore distances combined by Matthiessen's rule. KW - thermal conductivity KW - mesoporous silicon KW - porosity KW - spark plasma KW - sintering KW - nanoscale modeling Y1 - 2022 U6 - https://doi.org/10.1007/s12274-022-4123-y SN - 1998-0124 SN - 1998-0000 VL - 15 IS - 6 SP - 5663 EP - 5670 PB - Tsinghua Univ. Press CY - Beijing ER - TY - JOUR A1 - Schulz, Christian A1 - Lieutenant, Klaus A1 - Xiao, Jie A1 - Hofmann, Tommy A1 - Wong, Deniz A1 - Habicht, Klaus T1 - Characterization of the soft X-ray spectrometer PEAXIS at BESSY II JF - Journal of synchrotron radiation N2 - The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed. KW - resonant inelastic X-ray scattering KW - X-ray photoelectron spectroscopy KW - soft X-ray spectroscopy KW - soft X-ray beamline KW - X-ray emission KW - X-ray KW - absorption KW - BESSY II Y1 - 2020 U6 - https://doi.org/10.1107/S1600577519014887 SN - 1600-5775 VL - 27 SP - 238 EP - 249 PB - International Union of Crystallography CY - Chester ER - TY - GEN A1 - Schulz, Christian A1 - Lieutenant, Klaus A1 - Xiao, Jie A1 - Hofmann, Tommy A1 - Wong, Deniz A1 - Habicht, Klaus T1 - Characterization of the soft X-ray spectrometer PEAXIS at BESSY II T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1355 KW - resonant inelastic X-ray scattering; KW - X-ray photoelectron spectroscopy KW - soft X-ray spectroscopy KW - soft X-ray beamline KW - X-ray emission KW - X-ray absorption KW - BESSY II. Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549928 SN - 1866-8372 ER - TY - JOUR A1 - Wolff, Nora A1 - Klimm, Detlef A1 - Habicht, Klaus A1 - Fritsch, Katharina T1 - Crystal growth and thermodynamic investigation of Bi2M2+O4 (M = Pd, Cu) JF - CrystEngComm / The Royal Society of Chemistry N2 - Phase equilibria that are relevant for the growth of Bi2MO4 have been studied experimentally, and the ternary phase diagrams of Bi2O3-PdO2-Pd and Bi2O3-Cu2O-CuO and its isopleth section Bi2O3-CuO were redetermined. It is shown that every melting and crystallization process is always accompanied by a redox process at the phase boundary and that for both title compounds, the valence of the transition metal is lowered during melting. Vice versa, during crystal growth, O-2 must be transported through the melt to the phase boundary. Based on these new insights provided by our thermodynamic studies, Bi2CuO4 single crystals with a length of up to 7 cm and a diameter of 6 mm were grown by the OFZ technique to be used for investigations of magnetic, electronic and thermal transport properties. The grown crystals were characterized by powder X-ray diffraction, Laue, magnetization and specific heat measurements. Y1 - 2021 U6 - https://doi.org/10.1039/d1ce00220a SN - 1466-8033 VL - 23 IS - 17 SP - 3230 EP - 3238 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Crovetto, Andrea A1 - Kojda, Danny A1 - Yi, Feng A1 - Heinselman, Karen N. A1 - LaVan, David A. A1 - Habicht, Klaus A1 - Unold, Thomas A1 - Zakutayev, Andriy T1 - Crystallize It before It diffuses BT - kinetic stabilization of thin-film phosphorus-rich semiconductor CuP2 JF - Journal of the american chemical society N2 - Numerous phosphorus-rich metal phosphides containing both P-P bonds and metal-P bonds are known from the solid-state chemistry literature. A method to grow these materials in thin-film form would be desirable, as thin films are required in many applications and they are an ideal platform for high-throughput studies. In addition, the high density and smooth surfaces achievable in thin films are a significant advantage for characterization of transport and optical properties. Despite these benefits, there is hardly any published work on even the simplest binary phosphorus-rich phosphide films. Here, we demonstrate growth of single-phase CuP2 films by a two-step process involving reactive sputtering of amorphous CuP2+x and rapid annealing in an inert atmosphere. At the crystallization temperature, CuP2 is thermodynamically unstable with respect to Cu3P and P-4. However, CuP2 can be stabilized if the amorphous precursors are mixed on the atomic scale and are sufficiently close to the desired composition (neither too P poor nor too P rich). Fast formation of polycrystalline CuP2, combined with a short annealing time, makes it possible to bypass the diffusion processes responsible for decomposition. We find that thin-film CuP2 is a 1.5 eV band gap semiconductor with interesting properties, such as a high optical absorption coefficient (above 10(5) cm(-1)), low thermal conductivity (1.1 W/(K m)), and composition-insensitive electrical conductivity (around 1 S/cm). We anticipate that our processing route can be extended to other phosphorus-rich phosphides that are still awaiting thin-film synthesis and will lead to a more complete understanding of these materials and of their potential applications. Y1 - 2022 U6 - https://doi.org/10.1021/jacs.2c04868 SN - 0002-7863 SN - 1520-5126 VL - 144 IS - 29 SP - 13334 EP - 13343 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Groitl, Felix A1 - Keller, Thomas A1 - Habicht, Klaus T1 - Generalized resolution matrix for neutron spin-echo three-axis spectrometers JF - Journal of applied crystallography N2 - This article describes the energy resolution of spin-echo three-axis spectrometers (SE-TASs) by a compact matrix formalism. SE-TASs allow one to measure the line widths of elementary excitations in crystals, such as phonons and magnons, with an energy resolution in the mu eV range. The resolution matrices derived here generalize prior work: (i) the formalism works for all crystal structures; (ii) spectrometer detuning effects are included; these arise typically from inaccurate knowledge of the excitation energy and group velocity; (iii) components of the gradient vector of the dispersion surface d omega/dq perpendicular to the scattering plane are properly treated; (iv) the curvature of the dispersion surface is easily calculated in reciprocal units; (v) the formalism permits analysis of spin-echo signals resulting from multiple excitation modes within the three-axis spectrometer resolution ellipsoid. KW - neutron spin-echo KW - neutron resonance spin-echo spectroscopy KW - resolution matrix KW - triple-axis spectroscopy Y1 - 2018 U6 - https://doi.org/10.1107/S1600576718005307 SN - 1600-5767 VL - 51 SP - 818 EP - 830 PB - International Union of Crystallography CY - Chester ER - TY - THES A1 - Habicht, Klaus T1 - Neutron-resonance spin-echo spectroscopy BT - a high resolution look at dispersive excitations Y1 - 2016 ER - TY - JOUR A1 - Mazzio, Katherine A. A1 - Kojda, Sandrino Danny A1 - Rubio-Govea, Rodrigo A1 - Niederhausen, Jens A1 - Ryll, Britta A1 - Raja-Thulasimani, Monika A1 - Habicht, Klaus A1 - Raoux, Simone T1 - P-type-to-n-type transition in hybrid AgxTe/PEDOT:PSS thermoelectric materials via stoichiometric control during solution-based synthesis JF - ACS applied energy materials N2 - This work demonstrates the production of high-performing p- type and n-type hybrid AgxTe/poly(3,4-ethylenedioxythiopene):polystyrene sulfonic acid (PE-DOT:PSS) thermoelectric materials from the same Te/PEDOT:PSS parent structure during aqueous-based synthesis. All samples were solution-processed and analyzed in thin- film architectures. We were able to demonstrate a power factor of 44 mu W m(-1) K-2 for our highest-performing n-type material. In addition, we were also able to realize a 68% improvement in the power factor of our p-type compositions relative to the parent structure through manipulation of the inorganic nanostructure composition. We demonstrate control over the thermoelectric properties by varying the stoichiometry of AgxTe nanoparticles in AgxTe/PEDOT:PSS hybrid materials via a topotactic chemical transformation process at room temperature. This process offers a simple, low-temperature, and cost-effective route toward the production of both efficient n-type and p-type hybrid thermoelectric materials. KW - thermoelectrics KW - hybrid material KW - PEDOT:PSS KW - tellurium KW - silver KW - telluride KW - hybrid synthesis Y1 - 2020 U6 - https://doi.org/10.1021/acsaem.0c01774 SN - 2574-0962 VL - 3 IS - 11 SP - 10734 EP - 10743 PB - ACS Publications CY - Washington, DC ER - TY - JOUR A1 - Panchal, Gyanendra A1 - Kojda, Sandrino Danny A1 - Sahoo, Sophia A1 - Bagri, Anita A1 - Kunwar, Hemant Singh A1 - Bocklage, Lars A1 - Panchwanee, Anjali A1 - Sathe, Vasant G. A1 - Fritsch, Katharina A1 - Habicht, Klaus A1 - Choudhary, Ram Janay A1 - Phase, Deodutta M. T1 - Strain and electric field control of magnetic and electrical transport properties in a magnetoelastically coupled Fe3O4/BaTiO3 (001) heterostructure JF - Physical review : B, Condensed matter and materials physics N2 - We present a study of the control of electric field induced strain on the magnetic and electrical transport properties in a magnetoelastically coupled artificial multiferroic Fe3O4/BaTiO3 heterostructure. In this Fe3O4/BaTiO3 heterostructure, the Fe3O4 thin film is epitaxially grown in the form of bilateral domains, analogous to a-c stripe domains of the underlying BaTiO3(001) substrate. By in situ electric field dependent magnetization measurements, we demonstrate the extrinsic control of the magnetic anisotropy and the characteristic Verwey metal-insulator transition of the epitaxial Fe3O4 thin film in a wide temperature range between 20-300 K, via strain mediated converse magnetoelectric coupling. In addition, we observe strain induced modulations in the magnetic and electrical transport properties of the Fe3O4 thin film across the thermally driven intrinsic ferroelectric and structural phase transitions of the BaTiO3 substrate. In situ electric field dependent Raman measurements reveal that the electric field does not significantly modify the antiphase boundary defects in the Fe3O4 thin film once it is thermodynamically stable after deposition and that the modification of the magnetic properties is mainly caused by strain induced lattice distortions and magnetic anisotropy. These results provide a framework to realize electrical control of the magnetization in a classical highly correlated transition metal oxide. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevB.105.224419 SN - 2469-9950 SN - 2469-9969 VL - 105 IS - 22 PB - The American Institute of Physics CY - Woodbury, NY ER -