Publication list of the Group of Materials in Electrical Engineering

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Schulz, Alexander; Bartsch, Heike; Gutzeit, Nam; Matthes, Sebastian; Glaser, Marcus; Ruh, Andreas; Müller, Jens; Schaaf, Peter; Bergmann, Jean Pierre; Wiese, Steffen
Characterization of reactive multilayer systems deposited on LTCC featuring different surface morphologies. - In: MikroSystemTechnik, (2021), S. 506-510

Baloochi, Mostafa; Shekhawat, Deepshikha; Riegler, Sascha Sebastian; Matthes, Sebastian; Glaser, Marcus; Schaaf, Peter; Bergmann, Jean Pierre; Gallino, Isabella; Pezoldt, Jörg
Influence of initial temperature and convective heat loss on the self-propagating reaction in Al/Ni multilayer foils. - In: Materials, ISSN 1996-1944, Bd. 14 (2021), 24, 7815, insges. 15 S.

A two-dimensional numerical model for self-propagating reactions in Al/Ni multilayer foils was developed. It was used to study thermal properties, convective heat loss, and the effect of initial temperature on the self-propagating reaction in Al/Ni multilayer foils. For model adjustments by experimental results, these Al/Ni multilayer foils were fabricated by the magnetron sputtering technique with a 1:1 atomic ratio. Heat of reaction of the fabricated foils was determined employing Differential Scanning Calorimetry (DSC). Self-propagating reaction was initiated by an electrical spark on the surface of the foils. The movement of the reaction front was recorded with a high-speed camera. Activation energy is fitted with these velocity data from the high-speed camera to adjust the numerical model. Calculated reaction front temperature of the self-propagating reaction was compared with the temperature obtained by time-resolved pyrometer measurements. X-ray diffraction results confirmed that all reactants reacted and formed a B2 NiAl phase. Finally, it is predicted that (1) increasing thermal conductivity of the final product increases the reaction front velocity; (2) effect of heat convection losses on reaction characteristics is insignificant, e.g., the foils can maintain their characteristics in water; and (3) with increasing initial temperature of the foils, the reaction front velocity and the reaction temperature increased.



https://doi.org/10.3390/ma14247815
Wu, Xuping; Chen, Honglei; Luo, Xuemei; Wang, Dong; Schaaf, Peter; Zhang, Guangping
Ultrasensitive strain sensors based on Cu-Al alloy films with voided cluster boundaries. - In: Advanced Materials Technologies, ISSN 2365-709X, Bd. 6 (2021), 12, 2100524, insges. 12 S.

https://doi.org/10.1002/admt.202100524
Cheng, Pengfei; Ziegler, Mario; Ripka, Valentin; Wang, Dong; Wang, Hongguang; Aken, Peter Antonie van; Schaaf, Peter
Bio-inspired self-assembly of large area 3D AgSiO2 plasmonic nanostructures with tunable broadband light harvesting. - In: Applied materials today, ISSN 2352-9407, Bd. 25 (2021), 101238

Tremendous efforts have been made to fabricate large-scale plasmonic nanostructures, which show wide applications in surface plasmon resonance (SPR) sensing, catalytic conversion, photothermal conversion, optoelectronics, photothermal therapy. However, unable to fabricate over 5 cm^2 plasmonic nanostructures with good controllability hinders their further applications. Here, super large-scale (153 cm^2) 3D AgSiO2 hybrid plasmonic nanostructures with adjustable and ultra-broadband light absorption are fabricated by a simple and controllable two-step approach. The metastable atomic layer deposition (MS-ALD) is combined with physical vapor deposition (PVD) to generate these structures in a self-assembly manner. The structures look like coral tentacles. These excellent properties are attributed to multiple forward scatterings and extinction effects produced by Ag@SiO2 nanostructures. Using 3D Ag@SiO2 plasmonic nanostructures as light absorber for bottom-heating-based evaporation, the water evaporation rate remarkably improves seven times under 1 Sun than that in dark condition. Our results pave the avenue for developing super large-scale Ag-based plasmonic nanostructure with potential applications in solar energy conversion.



https://doi.org/10.1016/j.apmt.2021.101238
Sauni Camposano, Yesenia Haydee; Riegler, Sascha Sebastian; Jaekel, Konrad; Schmauch, Jörg; Pauly, Christoph; Schäfer, Christian; Bartsch, Heike; Mücklich, Frank; Gallino, Isabella; Schaaf, Peter
Phase transformation and characterization of 3D reactive microstructures in nanoscale Al/Ni multilayers. - In: Applied Sciences, ISSN 2076-3417, Bd. 11 (2021), 19, 9304, S. 1-13

Reactive multilayer systems represent an innovative approach for potential usage in chip joining applications. As there are several factors governing the energy release rate and the stored chemical energy, the impact of the morphology and the microstructure on the reaction behavior is of great interest. In the current work, 3D reactive microstructures with nanoscale Al/Ni multilayers were produced by alternating deposition of pure Ni and Al films onto nanostructured Si substrates by magnetron sputtering. In order to elucidate the influence of this 3D morphology on the phase transformation process, the microstructure and the morphology of this system were characterized and compared with a flat reactive multilayer system on a flat Si wafer. The characterization of both systems was carried out before and after a rapid thermal annealing treatment by using scanning and transmission electron microscopy of the cross sections, selected area diffraction analysis, and differential scanning calorimetry. The bent shape of multilayers caused by the complex topography of silicon needles of the nanostructured substrate was found to favor the atomic diffusion at the early stage of phase transformation and the formation of two intermetallic phases Al0.42Ni0.58 and AlNi3, unlike the flat multilayers that formed a single phase AlNi after reaction.



https://doi.org/10.3390/app11199304
Biele, L.; Schmid, F.; Schaaf, Peter
Temperatur- und Druckabhängigkeit des elektrischen Kontaktwiderstands von Kupfer. - In: DVS Congress 2021, (2021), S. 536-542

Yan, Yong; Liu, Haocen; Liu, Chunyue; Zhao, Yuguo; Liu, Shuzhen; Wang, Dong; Fritz, Mathias; Ispas, Adriana; Bund, Andreas; Schaaf, Peter; Wang, Xiayan
Efficient preparation of Ni-M (M = Fe, Co, Mo) bimetallic oxides layer on Ni nanorod arrays for electrocatalytic oxygen evolution. - In: Applied materials today, ISSN 2352-9407, Bd. 25 (2021), 101185

Fabrication of economic and high-performance electrodes for electrocatalytic oxygen evolution reaction (OER) accounts for a crucial issue associated with developing powerful and practical water splitting systems. In this work, free-standing Ni/Ni-M (M = Fe, Co, Mo) bimetallic oxides core/shell nanorod arrays (Ni/Ni-M NRAs) were prepared through electroless deposition of transition metal species on black nickel sheet (nickel nanorod arrays (Ni NRAs)) followed by electrochemical oxidation. All three types of Ni/Ni-M NRAs demonstrated enhanced electrocatalytic activity toward oxygen evolution reactions (OER). Especially, Ni/Ni-Fe NRAs electrode exhibit small onset potential of 1.535 V at current density of 10 mA&hahog;cm^-2. In contrast, the OER durability of these three samples was distinct. At 500 mV constant overpotential, the current density loss in OER of Ni/Ni-Fe NRAs was merely 13.5% for a period of 20000 s; but Ni/Ni-Mo and Ni/Ni-Co NRAs had almost disappeared catalytic activity under the identical conditions. According to many reports, the results were different for the superior OER stability of Ni-based bimetallic catalysts. Electrochemical analysis revealed that the NRAs structure dramatically improves charge transfer efficiency and electrochemically active surface area (ECSA). The present study might provide a new insight to design and fabricate more practical and high-performance Ni-based electrodes for OER.



https://doi.org/10.1016/j.apmt.2021.101185
Herre, Patrick; Will, Johannes; Dierner, Martin; Wang, Dong; Yokosawa, Tadahiro; Zech, Tobias; Wu, Mingjian; Przybilla, Thomas; Romeis, Stefan; Unruh, Tobias; Peukert, Wolfgang; Spiecker, Erdmann
Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire. - In: Acta materialia, ISSN 1873-2453, Bd. 220 (2021), 117318, insges. 12 S.

Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0-28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct <111> out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain.



https://doi.org/10.1016/j.actamat.2021.117318
Biele, Lukas; Schaaf, Peter; Schmid, Florian
Specific electrical contact resistance of copper in resistance welding. - In: Physica status solidi, ISSN 1862-6319, Bd. 218 (2021), 19, 2100224, insges. 11 S.

The electrical contact resistance (ECR) of copper (Cu-ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20-550 &ring;C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature-dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects.



https://doi.org/10.1002/pssa.202100224
Hergert, Germann; Wöste, Andreas; Vogelsang, Jan; Quenzel, Thomas; Wang, Dong; Groß, Petra; Lienau, Christoph
Probing transient localized electromagnetic fields using low-energy point-projection electron microscopy. - In: ACS photonics, ISSN 2330-4022, Bd. 8 (2021), 9, S. 2573-2580

Low kinetic energy electrons are of interest for probing nanoscale dynamic processes using ultrafast electron microscopy techniques. Their low velocities reduce radiation doses and enhance the interaction with confined electromagnetic fields and, thus, may enable ultrafast spectroscopy of single nanostructures. Recent improvements in the spatial and temporal resolution of ultrafast, low-energy electron microscopy have been achieved by combining nanotip photoemitters and point-projection imaging schemes. Here, we use such an ultrafast point-projection electron microscope (UPEM) to analyze the interaction of low-energy electrons with transient electric fields created by photoemission from a nanogap antenna. By analyzing their kinetic energy distribution, we separate angular deflection due to radial field components from electron energy gain and loss due to their axial acceleration. Our measurements open up a route toward the spatial and temporal characterization of vectorial near-fields by low-energy electron streaking spectroscopy.



https://doi.org/10.1021/acsphotonics.1c00775