Effect of partial and global shielding on surface-driven phenomena in keyhole mode laser beam welding. - In: Welding in the world, ISSN 1878-6669, Bd. 68 (2024), 6, S. 1353-1374
Partial shielding by means of local gas supply has proven to be very effective in reducing spatter. Besides the effect of gas-induced dynamic pressure, the shielding of oxygen is also highly relevant for melt pool dynamics and spatter formation due to the growth of oxides and the influence on surface tension. Therefore, this paper addresses the effect of local supplied argon on oxide growth and seam topography during keyhole mode laser beam welding of high-alloy steel AISI 304. To determine the shielding quality, the results are compared to laser beam welding in a global argon atmosphere. The topography of the upper weld seams was analyzed by scanning electron microscopy (SEM). An X-ray microanalysis (EDX) in line scan modus was performed to determine and to locate the elements which are covering the specimen surface. The chemical state of the found elements was quantified by X-ray photoelectron spectroscopy (XPS). In a last step, high-speed synchrotron X-ray imaging was performed to separate the effect of the gas-induced pressure and the gas-induced shielding on keyhole geometry. The results show that a local supply of argon contributes to a significant difference in oxide growth, affecting melt pool convection and weld seam geometry. It was further shown that the effect of gas flows at low flow rates is primarily because of oxygen shielding, as no significant difference in keyhole geometry was found by high-speed synchrotron X-ray imaging.
https://doi.org/10.1007/s40194-023-01627-y
Adaptation of metrology-grade ac current source in velocity mode of Planck-Balance 2: direct referencing induced voltages with ac quantum voltage standard. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 1, 015026, S. 1-11
The adaptation of developed metrology-grade ac current source (MCS) to the velocity mode of measurements of the Planck-Balance 2 as a means for generating ac mechanical oscillations is presented. The universality in operating with the MCS unit especially practical for the Planck-Balance setup for frequencies of 0.1 Hz-20 Hz (including but not limited to the negligence of a broader range of 0.01 Hz up to several hundred Hz) and for amplitudes of up to 10 mA with 16 (offset with 14)-bit effective resolution is demonstrated. MCS allows generating complex ac waveform signals as waveform synthesizers by adding to the original signal an extra five independent harmonic components, each of which with an adjustable resolution of 10 ns for phase and 16-bit for amplitude. Additionally, the MCS is supported by an external clock at 10 MHz frequency which serves also as a common reference time base for the comparison between the direct output signal of MCS, or of the induced voltage in the coil of the Planck-Balance resulting due to the applied current by MCS, with the ac quantum voltage standard at the required accuracy levels.
https://doi.org/10.1088/1361-6501/ad006c
Dual-functional electrode promoting dendrite-free and CO2 utilization enabled high-reversible symmetric Na-CO2 batteries. - In: Energy & Environmental Materials, ISSN 2575-0356, Bd. 7 (2024), 3, e12626, S. 1-10
Sodium-carbon dioxide (Na-CO2) batteries are regarded as promising energy storage technologies because of their impressive theoretical energy density and CO2 reutilization, but their practical applications are restricted by uncontrollable sodium dendrite growth and poor electrochemical kinetics of CO2 cathode. Constructing suitable multifunctional electrodes for dendrite-free anodes and kinetics-enhanced CO2 cathodes is considered one of the most important ways to advance the practical application of Na-CO2 batteries. Herein, RuO2 nanoparticles encapsulated in carbon paper (RuCP) are rationally designed and employed as both Na anode host and CO2 cathode in Na-CO2 batteries. The outstanding sodiophilicity and high catalytic activity of RuCP electrodes can simultaneously contribute to homogenous Na+ distribution and dendrite-free sodium structure at the anode, as well as strengthen discharge and charge kinetics at the cathode. The morphological evolution confirmed the uniform deposition of Na on RuCP anode with dense and flat interfaces, delivering enhanced Coulombic efficiency of 99.5% and cycling stability near 1500 cycles. Meanwhile, Na-CO2 batteries with RuCP cathode demonstrated excellent cycling stability (>350 cycles). Significantly, implementation of a dendrite-free RuCPNa anode and catalytic-site-rich RuCP cathode allowed for the construction of a symmetric Na-CO2 battery with long-duration cyclability, offering inspiration for extensive practical uses of Na-CO2 batteries.
https://doi.org/10.1002/eem2.12626
The role of vacancy dynamics in two-dimensional memristive devices. - In: Advanced electronic materials, ISSN 2199-160X, Bd. 10 (2024), 1, 2300635, S. 1-18
Two-dimensional layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of defect dynamics in the switching process of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. It explains the distinct features of the device characteristics observed experimentally, including fundamentally different device behavior previously thought to originate from multiple mechanisms. Key influence factors are identified and discussed with a fully coupled and dynamic charge transport model for electrons, holes, and ionic point defects, including image-charge-induced Schottky barrier lowering (SBL). Thermal effects and local Joule heating are considered by coupling the transient heat transfer equation to the electronic properties. The model is validated with hysteresis and pulse measurements for various lateral 2D MoS2-based devices, strongly corroborating the relevance of vacancy dynamics in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications.
https://doi.org/10.1002/aelm.202300635
Field-responsive fluid based multi-degree-of-freedom dampers for independently adjustable dissipation. - In: Calm, smooth and smart, (2024), S. 305-324
Damping is a decisive factor that influences the dissipation of energy in vibrating systems. That is why it is important to have the right amount of damping in vibrating systems. Magneto (MR)- and electrorheological (ER) fluids have been implemented in damper technology as a novel invention two decades ago, whereby the resulted damping can be adjusted in real-time by controlling the strength of the applied field. Since the damping can be adjusted, the damper is categorized as a smart system in which a smooth transition and calm operation can be achieved in a vibrating system. Even though MR and ER fluid-based dampers have been implemented in a few mass-production applications and investigated in many scientific studies, these pure damper elements do operate only in one direction of motion. In this work, multi-degree-of-freedom (M-DOF) MR/ER dampers are aimed. Ideas for new possibilities in extending their functionality by going beyond the conventional ER/MR damper design are explored. For this reason, the known operating modes and damper designs are extended in new directions. Three general extension possibilities are explored and investigated through experiments, namely the extension (1) by integrating several damper elements, (2) by combining known operating modes, and (3) by adding extra control elements. The construction of the damper systems including the investigation results are presented. As a result, the investigation has proven that M-DOF MR/ER dampers can be realized using these extension approaches. It shows even a prospect of making the damper system to be more compact despite a higher complexity. The work has shown that there are still a lot of possibilities for exploring the MR/ER damper design.
https://doi.org/10.1007/978-3-031-36143-2_16
A universal design strategy based on NiPS3 nanosheets towards efficient photothermal conversion and solar desalination. - In: Advanced functional materials, ISSN 1616-3028, Bd. 34 (2024), 8, 2310942, S. 1-11
2D nanomaterials are proposed as promising photothermal materials for interfacial photothermal water evaporation. However, low evaporation efficiency, the use of hazardous hydrofluoric solution, and poor stability severely limit their practical applications. Here, a mixed solvent exfoliation surface deposition (MSESD) strategy for the preparation of NiPS3 nanosheets and NiPS3/polyvinyl alcohol (PVA) converter is successfully developed. The converter is obtained by drop-casting the NiPS3/PVA nanosheets onto a sponge. The PVA is mainly deposited on the edge of NiPS3 nanosheets, which not only improves the stability of NiPS3 nanosheets, but also adheres to the sponge to prepare a 3D photothermal converter, which shows an evaporation rate of 1.48 kg m−2 h−1 and the average photothermal conversion efficiency (PTCE) of 93.5% under a light intensity of 1 kW m−2. The photothermal conversion mechanism reveals that the energy of absorbed photons in NiPS3 nanosheets can be effectively converted into heat through non-radiative photon transitions as well as multiple optical interactions. To the best of the knowledge, this is the first report on the application of 2D metal-phosphorus-chalcogen (MPChx) for solar desalination, which provides new insights and guidance for the development of high-performance 2D photothermal materials.
https://doi.org/10.1002/adfm.202310942
Exploring the surface oxidation and environmental instability of 2H-/1T’-MoTe2 using field emission based scanning probe lithography. - In: Advanced materials, ISSN 1521-4095, Bd. 36 (2024), 4, 2310887, S. 1-14
An unconventional approach for the resistless nanopatterning 2H- and 1T’-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60 eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide was characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3/MoOx as well as TeO2/TeOx. With the presented technology in combination with subsequent AFM imaging it was possible to demonstrate a strong anisotropic sensitivity of 1T’-/(Td)-MoTe2 to aqueous environments. We finally used the discussed approach to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet. This article is protected by copyright. All rights reserved
https://doi.org/10.1002/adma.202310887
Influence of the reference surface and AFM tip on the radius and roundness measurement of micro spheres. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 2, 025010, S. 1-16
The performance of tactile and optical surface sensors for nano and micro coordinate measuring machines is currently limited by the lack of precisely characterised micro spheres, since established strategies have mainly been developed for spheres in the range of millimetres or above. We have, therefore, recently focused our research efforts towards a novel strategy for the characterisation of spheres in the sub-millimetre range. It is based on a set of atomic force microscope (AFM) surface scans in conjunction with a stitching algorithm. To obtain an uncertainty statement, the uncertainty about the shape of the reference surface needs to be propagated via the shape of the AFM tip to the actual measurement object. However, the sampling process of an AFM is non-linear and the processing of AFM scans requires complex algorithms. We have, therefore, recently begun to model the characterisation of micro spheres through simulations. In this contribution, this model is extended by the influence of the tip and reference surface. The influence of the tip’s shape and reference surface is investigated through virtual and real experiments. The shape of the tip is varied by using tips with mean radii of 200 nm and 2 μm while sampling the same ruby sphere with a mean radius of 150 μm. In general, the simulation results imply that an uncertainty of less then 10 nm is achievable. However, an experimental validation of the model is still pending. The experimental investigations were limited by the lack of a suitable cleaning strategy for micro parts, which demonstrates the need for further investigations in this area. Although the characterisation of a full sphere has already been demonstrated, the investigations in this contribution are limited to equator measurements.
https://doi.org/10.1088/1361-6501/ad03b7
High performance photothermal carbon nanotubes/nanostructured hydrogel for solar electricity production and solar water sterilization. - In: Applied surface science, Bd. 643 (2024), 158680
Solar energy is a promising renewable energy source with the potential to contribute to sustainable development. Efficient photothermal conversion is critical for solar energy acquisition and conversion. Here, carbon nanotubes (CNTs) were gelatinized to obtain the nanostructured CNT/hydrogel, and then highly light-absorbing CNT/n-hydrogels with surface texture were obtained by replicating the micrometer structure from the black silicon (b-Si) surface onto CNT/hydrogels by using a PDMS mold. Through the synergistic effect of both surface texture and nanostructures, it demonstrates high efficiency of solar electricity production and solar sterilization. A small thermoelectric (TE) module with an area of 4 × 4 cm2 is integrated with CNT/n-hydrogel absorber for the investigation of photo-thermoelectric conversion. The output power of the CNT/n-hydrogel TE device is 1.42 W•m−2 under 1 sun. And by connecting four devices in series, it has successfully demonstrated for charging mobile phones under two different solar illuminations. This work provides a cost-effective and easy fabrication method for opening up the hydrogel as a photothermal absorber, which is low-cost, reproducible, high-efficiency solar water sterilization and high photothermal conversion efficiency.
https://doi.org/10.1016/j.apsusc.2023.158680
High-resolution patterning on LTCC by transfer of photolithography-based metallic microstructures. - In: International journal of applied ceramic technology, ISSN 1744-7402, Bd. 21 (2024), 2, S. 1180-1190
The growing applications and constant miniaturization of electronic devices and of low-temperature co-fired ceramics (LTCC) in various fields, such as aviation, telecommunications, automotive, satellite communications, and military, have led to an increase in the demand for LTCC. Such prospects arise due to the continuous scaling down of components and high-density interconnection in electronics packaging. This paper reports a technique for the transfer of high-resolution microstructures from silicon substrates to LTCC. In this method, gold and copper patterns were formed by photolithography, electrodeposition, and residual layer stripping on silicon substrate. Lithography provides the opportunity to create and transfer complex patterns for use in several different applications and electroplating enables the use of pure metal for excellent electrical properties. The developed structures were transferred onto a top layer of LTCC tape using hot embossing. Then, the subsequent layers were stacked, laminated, and sintered. A resolution of 1.5 μm after free sintering and 4.5 μm after pressure-assisted sintering was achieved. This distinctive method can be useful for several applications requiring high-resolution and superior electrical properties.
https://doi.org/10.1111/ijac.14569