Confirming the unusual temperature dependence of the electric-field gradient in Zn. - In: Crystals, ISSN 2073-4352, Bd. 12 (2022), 8, 1064, S. 1-8
The electric-field gradient (EFG) at nuclei in solids is a sensitive probe of the charge distribution. Experimental data, which previously only existed in insulators, have been available for metals with the development of nuclear measuring techniques since about 1970. An early, systematic investigation of the temperature dependence of the EFG in metals, originally based on results for Cd, but then also extended to various other systems, has suggested a proportionality to T3/2. However, later measurements in the structurally and electronically similar material Zn, which demonstrated much more complex behavior, were largely ignored at the time. The present experimental effort has confirmed the reliability of this unexpected behavior, which was previously unexplained.
https://doi.org/10.3390/cryst12081064
The angle dependent ΔE effect in TiN/AlN/Ni micro cantilevers. - In: Sensors and actuators, ISSN 1873-3069, Bd. 345 (2022), 113784, S. 1-12
In this work, magnetoelectric MEMS sensors based on a TiN/AlN/Ni laminate are investigated for the first time in regards of the anisotropic elastic properties when using hard magnetic Nickel as magnetostrictive layer. The implications of crystalline, uniaxial and shape anisotropy are analysed arising from the anisotropic ΔE effect in differently oriented cantilevers with 25 µm length and 15˚ spacing. The ΔE effect is derived analytically to consider the angular dependency of the different anisotropies within the sensors. In the measured frequency spectra complex profiles are observable consisting of contributions from neighbouring structures which are connected by a common electrode. The crosstalk effect is strongly depending on the cantilever orientation and reflects the anisotropic mechanical properties of the material stack. The intensity of the crosstalk effect is increasing for shortened cantilevers and narrowing distance between structures. The ΔE effect is investigated based on cantilevers of different angular spacing and of a single cantilever that is rotated in the magnetic field. The derived peak sensitivities are reaching values of 1.15 and 1.31T-1. The angular dependency of the sensitivity is found to be approximately constant for differently oriented cantilevers. In contrast, for a singly rotated cantilever an angular dependency of the 4th order is observed.
https://doi.org/10.1016/j.sna.2022.113784
MOCVD surface preparation of V-groove Si for III-V growth. - In: Journal of crystal growth, Bd. 597 (2022), 126843
V-groove nanopatterning of Si substrates has recently demonstrated promise for achieving high-quality III-V-on-Si epitaxy while providing a lower-cost processing route than chemo-mechanical polishing to produce epi-ready planar wafers. A key factor in determining the crystalline quality of III-V buffer layers is the Si surface structure and its chemical composition. Unlike planar Si surfaces, the surfaces of V-grooves prior to growth have not been studied in detail. Here, we study the surface of V-groove Si prepared for GaP nucleation via X-ray photoelectron spectroscopy and low-energy electron diffraction. We identify several pretreatments, using both 830˚C and 1000˚C annealing under an As background pressure, as being suitable for deoxidizing and cleaning the V-groove Si surface. The V-groove Si was found to behave similarly to reference Si(0 0 1) and Si(1 1 1) planar samples, demonstrating that in situ techniques such as reflection anisotropy spectroscopy can be used on reference samples to infer the state of the V-groove surface, and indicating that the extensive research on planar Si surfaces can be directly applied to V-grooves.
https://doi.org/10.1016/j.jcrysgro.2022.126843
Combining advanced photoelectron spectroscopy approaches to analyse deeply buried GaP(As)/Si(100) interfaces : Interfacial chemical states and complete band energy diagrams. - In: Applied surface science, Bd. 605 (2022), 154630
The epitaxial growth of the polar GaP(100) on the nonpolar Si(100) substrate suffers from inevitable defects at the antiphase domain boundaries (APDs), resulting from mono-atomic steps on the Si(100) surface. Stabilization of Si(100) substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4-50-nm-thick GaP epitaxial films were grown on As-terminated Si(100) substrates with different types of doping, miscuts, and As-surface termination by metalorganic vapor phase epitaxy (MOVPE). The GaP(As)/Si(100) heterostructures were investigated by X-ray photoelectron spectroscopy (XPS) combined with gas cluster ion beam (GCIB) sputtering and by hard X-ray photoelectron spectroscopy (HAXPES). We found residuals of As atoms in the GaP lattice (∼0.2-0.3 at.%) and a localization of As atoms at the GaP(As)/Si(100) interface (∼1 at.%). Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle-resolved XPS measurements. Similar valence band offset (VBO) values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As-terminated Si substrate surface. The band alignment diagram of the GaP(As)/Si(1 0 0) heterostructure was deduced.
https://doi.org/10.1016/j.apsusc.2022.154630
Elektrochemisches Glätten von Metallen durch ionenleitende Festkörper in schwach leitenden Lösungen. - In: WOMag, ISSN 2195-5891, Bd. 11 (2022), 6, S. 22-24
Elektrochemische Abscheidung von Silicium aus organischen Elektrolyten. - In: Galvanotechnik, ISSN 0016-4232, Bd. 113 (2022), 7, S. 877-887
Silicium (Si) ist ein wichtiger Rohstoff für viele industrielle Anwendungen, u. a. für die Mikroelektronik, die Photovoltaikindustrie und neuerdings auch innerhalb der elektrochemischen Energiespeicherung. Für die Erweiterung des technischen Anwendungsspektrums von Si sind jedoch anpassbare Abscheidungstechnologien erforderlich.
Electrodeposition of high entropy alloy of Ni-Co-Cu-Mo-W from an aqueous bath. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Bd. 169 (2022), 8, 082515, insges. 5 S.
This study aimed to deposit high entropy alloy (HEA) coatings with five different elements, Ni, Co, Cu, Mo, and W, from a single aqueous bath. The influence of pH, current density, and complex agent on the composition of deposited coating was examined. It was shown that Mo and W were codeposited mainly with Ni and Co. pH had the most impact on the codeposition of reluctant elements like Mo and W, while current density had the minimum effect. The deposited coating had a metallic, dense, and nodular morphology with configurational entropy of around 1.6 R.
https://doi.org/10.1149/1945-7111/ac87d5
A review on photothermal conversion of solar energy with nanomaterials and nanostructures: from fundamentals to applications. - In: Advanced sustainable systems, ISSN 2366-7486, Bd. 6 (2022), 9, 2200115, S. 1-19
Solar energy is a green, sustainable, and de facto inexhaustible energy source for mankind. The conversion of solar energy into other forms of energy has attracted extensive research interest due to climate change and the energy crisis. Among all the solar energy conversion technologies, photothermal conversion of solar energy exhibits unique advantages when applied for water purification, desalination, high-temperature heterogeneous catalysis, anti-bacterial treatments, and deicing. In this review, the various photothermal conversion mechanisms based on different forms of heat release are summarized and some of the latest examples are presented. In addition, the necessary prerequisites for solar-driven photothermal materials toward their practical applications are also discussed. Further, the latest advances in photothermal conversion of solar energy are discussed, focusing on different types of photothermal applications. Finally, a summary is given and the challenges and opportunities in the photothermal conversion of solar energy are presented. This review aims to give a comprehensive understanding of emerging solar energy conversion technologies based on the photothermal effect, especially by using nanomaterials and nanostructures.
https://doi.org/10.1002/adsu.202200115
Highly efficient passive Tesla valves for microfluidic applications. - In: Microsystems & nanoengineering, ISSN 2055-7434, Bd. 8 (2022), 1, 97, S. 1-12
A multistage optimization method is developed yielding Tesla valves that are efficient even at low flow rates, characteristic, e.g., for almost all microfluidic systems, where passive valves have intrinsic advantages over active ones. We report on optimized structures that show a diodicity of up to 1.8 already at flow rates of 20 μl s^-1 corresponding to a Reynolds number of 36. Centerpiece of the design is a topological optimization based on the finite element method. It is set-up to yield easy-to-fabricate valve structures with a small footprint that can be directly used in microfluidic systems. Our numerical two-dimensional optimization takes into account the finite height of the channel approximately by means of a so-called shallow-channel approximation. Based on the three-dimensionally extruded optimized designs, various test structures were fabricated using standard, widely available microsystem manufacturing techniques. The manufacturing process is described in detail since it can be used for the production of similar cost-effective microfluidic systems. For the experimentally fabricated chips, the efficiency of the different valve designs, i.e., the diodicity defined as the ratio of the measured pressure drops in backward and forward flow directions, respectively, is measured and compared to theoretical predictions obtained from full 3D calculations of the Tesla valves. Good agreement is found. In addition to the direct measurement of the diodicities, the flow profiles in the fabricated test structures are determined using a two-dimensional microscopic particle image velocimetry (μPIV) method. Again, a reasonable good agreement of the measured flow profiles with simulated predictions is observed.
https://doi.org/10.1038/s41378-022-00437-4
Development of a production process for environmentally friendly and resource-efficient molded parts consisting of load-appropriate reinforced wood-plastic composites :
Entwicklung eines Herstellungsprozesses für umweltfreundliche und ressourceneffiziente Formteile aus lastgerecht verstärkten Holz-Kunststoff-Verbunden. - In: Zeitschrift Kunststofftechnik, Bd. 18 (2022), 4, S. 203-233
Dieser Beitrag beschreibt einen Herstellungsprozess für umweltfreundliche und ressourceneffiziente Formteile aus neuartigen Holz-Kunststoff-Verbunden (HKV). Bei der Herstellung von HKV werden anisotrope mechanische Eigenschaften von langen, schlanken Holzspänen (Strands) durch deren lastgerechte Positionierung auf dreidimensionaler Werkzeugoberfläche anwendungsoptimiert ausgenutzt und umweltverträgliche duro- als auch thermoplastische Kunststoffe als Alternative zu den konventionellen formaldehyd- oder isocyanathaltigen Bindemitteln eingesetzt.
https://dx.doi.org/10.3139/O999.01042022