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
Analysis of selective bonding processes using reactive multi-layers for system integration on LTCC based SiPs. - In: Microsystem technologies, ISSN 1432-1858, Bd. 28 (2022), 9, S. 1995-2009
This paper discusses the use of reactive multi-layers for selective assembly of ICs (Integrated Circuits) in an LTCC (Low Temperature Co-fired Ceramics) based SiP (System-in-Package). To understand the requirements for the use of self-propagating reactive multilayers in die bonding, CFD (Computational Fluid Dynamics) simulations have been carried out to simulate the die bonding process of a silicon chip onto a ceramic LTCC substrate. Reactive foils of 40 and 80 µm thicknesses and a simulated reaction propagation speed of 1 m/s were studied and used to melt a solder preform underneath a silicon chip. The results of the CFD simulations were analysed, particularly with respect to temperature and liquid fraction contours, as well as time-temperature histories obtained from temperature probes which were included in the model, such as to approximate the real behaviour of Pt-100 temperature probes, when a real bonding process is being tracked. The CFD method, in this instance realised with ANSYS Fluent software, can track the melting and solidification of the solder as well as model the influence of latent heat, which is crucial to ascertaining the true evolution of the bonding process.
https://doi.org/10.1007/s00542-022-05328-2
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
A combined velocity and temperature measurement with an LED and a low-speed camera. - In: Measurement science and technology, ISSN 1361-6501, Bd. 33 (2022), 11, 115301, S. 1-12
Microfluidic devices are governed by three-dimensional velocity and temperature fields, and their boundary conditions are often unknown. Therefore, a measurement technique is often desired to measure both fields in a volume. With astigmatism particle tracking velocimetry (APTV) combined with luminescence lifetime imaging, the temperature and all velocity components in a volume can be measured with one optical access. While the three-dimensional particle position is determined by evaluating the shape of the corresponding particle image, the temperature measurement relies on estimating the temperature-dependent luminescence lifetime derived from particle images on two subsequent image captures shortly after the photoexcitation. For this, typically a high-energetic pulsed laser is required to ensure a high signal-to-noise ratio. However, it can also cause additional heating of the fluid. We show that this problem is solved by replacing the pulsed laser with an LED. To compensate for the lower power provided by the LED, we adapted the timing schedule and vastly extended the illumination time and the exposure time for both image captures. In addition, we were able to replace the typically used high-speed camera with an ordinary double-frame camera. In this way, very low measurement uncertainties on all measured quantities can be achieved while keeping the temperature of the fluid unaffected. Random errors dominate within the two focal planes of APTV, yielding a standard deviation of the temperature of individual particles of about 1 only. The measurement error caused by the movement of tracer particles during the much longer illumination and exposure time were found to be acceptable when the measured velocity is low. With the circumvention of light-source induced heating and the lower cost of hardware devices, the adapted approach is a suitable measurement technique for microfluidic related research.
https://doi.org/10.1088/1361-6501/ac82da
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
Tandem nanostructures: a prospective platform for photoelectrochemical water splitting. - In: Solar RRL, ISSN 2367-198X, Bd. 6 (2022), 9, 2200181, S. 1-33
A platform for efficient photoelectrochemical (PEC) water splitting must fulfil different requirements: the absorption of the solar spectrum should be maximized in use for charge carrier generation. To avoid recombination, fast separation of charge carriers is required and the energetic positions of the band structure(s) must be optimized with respect to the water splitting reactions. In these respects, constructing tandem nanostructures with rationally designed nanostructured units offers a potential opportunity to break the performance bottleneck imposed by the unitary nanostructure. So far, quite a few tandem nanostructures have been designed, fabricated, and employed to improve the efficiency of PEC water splitting, and significant achievements have been realized. This review focuses on the current advances in tandem nanostructures for PEC water splitting. Firstly, the state of the art for tandem nanostructures applied in PEC water splitting is summarized. Secondly, the advances in this field and advantages arising of employing tandem nanostructures for PEC water splitting are outlined. Subsequently, different types of tandem nanostructures are reviewed, including core-shell tandem nanostructured photoelectrode, the two-photoelectrode tandem cell, and the tandem nanostructures of plasmon related devices for PEC water splitting. Based on this, the future perspective of this field is proposed.
https://doi.org/10.1002/solr.202200181
Accuracy assessment of simplified computation of active and passive magnetic shielding for optically pumped magnetometers. - In: IEEE transactions on magnetics, ISSN 1941-0069, Bd. 58 (2022), 9, 7401204, insges. 4 S.
A low residual environmental magnetic field is required for the proper operation of most optically pumped magnetometers (OPMs). This is achieved using a combination of passive and active magnetic shielding. Passive magnetic shielding often uses multiple layers of highly permeable materials. A realistic two-layer magnetically shielded room (MSR) for biomagnetic measurements is numerically studied using the finite element method. A measured B-H characteristic of Mumetal is used, which is linearly extrapolated from the Rayleigh region (RR) into the low magnetic field range. This extension of the magnetization curve yields no significant differences compared to using a constant permeability value for the low magnetic field range. Furthermore, we model the MSR with only one shield and apply a simple analytical method of images (MOI). The MOI yields on average a 100-fold reduction in computation time. The relative difference of the magnetic flux density computed with MOI and finite element method (FEM) is smaller than < 1% at the center of a spherical region of interest (ROI) with a radius of 0.3 m desired from the point of magnetoencephalography (MEG) using OPMs. The achieved accuracy of the MOI makes it suitable for the optimization of active shielding coils.
https://doi.org/10.1109/TMAG.2022.3161736