Journal articles and book contributions

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Tan, Xinu; Liu, Yushun; Li, Feitao; Qiu, Risheng; Liu, Qing
Formation of nanocrystalline γ-ZrH in Zr-Nb alloy: crystal structure and twinning. - In: Micron, ISSN 1878-4291, (2023), 103414

In the present work, the lattice parameter and the twins of γ-ZrH hydride in Zr-2.5Nb-1Si were characterized using high resolution electron microscopy. The lattice parameters of γ-ZrH (P42/mmc, Zr2H2 unit cell) is determined to be a= 0.336nm, c=0.508nm. Twinning γ-ZrH hydride ({011}<0̅11> type) is for the first time reported in zirconium alloys, whose orientation relationship with α-Zr is [100]γ-twins // [1̅210]α and (011)γ-twins // (0002)α. The formation process of γ-ZrH twins is also discussed based on a ‘grow-in’ mechanism during the transformation from α-Zr to γ-ZrH hydride.
Charfi, Bilel; Zekri, Mohamed; Herrmann, Andreas; Damak, Kamel; Maâlej, Ramzi
Atomic scale network structure of a barium aluminosilicate glass doped with different concentrations of rare-earth ions explored by molecular dynamics simulations. - In: Computational materials science, Bd. 218 (2023), 111965

Molecular dynamics (MD) simulation is employed for exploring the coordination of atoms in peralkaline BaO-Al2O3-SiO2 glasses of variable Gd3+ doping concentrations between 1 and 3.8 mol% Gd2O3. For this the MD simulation procedure of inherent structure sampling was used which provides statistically robust information on the local atomic surrounding of the doped rare earth ions. Distributions of Si/Al/Ba/Gd cations in the first, second and third coordination spheres are investigated. Special focus is laid on the effect of Gd3+ doping concentration on the local surrounding of the Gd3+ ions, i. e. rare earth clustering, and general glass structure. The simulations show that SiOAl bonds are preferred in comparison to SiOSi and AlOAl connections with respect to the random model predictions. Deviations from a statistical Si/Al distribution around the BaOp and GdOq polyhedra are observed. The network modifier ions are preferably surrounded by other network modifier ions, rather than by network formers. It is shown that the incorporation of Gd does not affect radial distribution functions, cumulative radial distribution function curves and the coordination sphere of Gd for Gd2O3 doping concentrations of up to 3.8 mol%, i.e. no rare earth clustering is observed. However, increasing Gd2O3 concentrations decrease the number of bridging oxygen and increase the number of non-bridging oxygen (NBO) species in the glass structure. Charge compensation of the additional non-bridging oxygen species is achieved by increasing NBO coordination numbers with Ba2+.
Glaser, Marcus; Matthes, Sebastian; Hildebrand, Jörg; Bergmann, Jean Pierre; Schaaf, Peter
Hybrid thermoplastic-metal joining based on Al/Ni multilayer foils - analysis of the joining zone. - In: Materials and design, ISSN 1873-4197, Bd. 226 (2023), 111561, insges. 16 S.

Multi material pairings like metal-plastic hybrid compounds are becoming increasingly important across all industrial sectors. However, the substitution of metals by plastics leads to a multitude of challenges based on the combination of dissimilar materials. The variations in the chemical and physical properties of the used materials require innovative joining processes. The application of reactive multilayers represents an advanced joining method for flexible and low-distortion joining of dissimilar joining partners by means of a short-term and localized application of thermal energy. In the context of this publication, the joining process between semi-crystalline polyamide 6 and austenitic stainless steel X5CrNi18-10(EN 1.4301 / AlSI304) based on reactive Al/Ni multilayers is investigated. In addition to evaluation of resulting joint strength, the focus of the work is in particular the characterization of the resulting failure behavior at the fracture interface under tensile load and the deriving binding mechanisms in the joint. From the results obtained, it is estimated that a direct bond can be generated between plastic and metal despite the presence of a residual reacted foil in the joining area. The structures present in the metal surface have a particularly positive influence on crack initiation and the resulting increased bond strength.
Li, Feitao; Tan, Xinu; Flock, Dominik; Qiu, Risheng; Wang, Dong; Schaaf, Peter
Formation of CuO whiskers and facet-controlled oxidation during the oxidation of Au-Cu nanoparticles fabricated by solid-state dewetting. - In: Applied surface science, Bd. 610 (2023), 155547

The fabrication of cupric oxide (CuO) nanowires from Cu particles via thermal oxidation provides a simple and scalable method to produce hierarchical structures. A stress-induced growth mechanism is believed to account for the nanowire formation while a slow oxidation rate is favored to sustain the driving force. Here, CuO whiskers are grown from Au-Cu nanoparticles because the formation of Au-Cu phases decreases the Cu diffusion rate and in turn slows down the oxidation rate. The driving force for the whisker growth is attributed to the compressive stress imposed by the CuO shell on the Au-Cu core, which is induced by the significantdifference in their linear thermal expansion coefficients. The contribution of the compressive stress is proved by the calculation. Moreover, preferred oxidation is observed and it is related to the crystalline structures of different facets existing on the surface of Au-Cu nanoparticles. The more compact the plane, the slower the diffusion rate through the plane, resulting in the formation of thinner CuO on the relevant facet. The results open a cost-effect way to fabricate hybrid nanostructures consisting of Cu-based core-shell nanoparticles attached with CuO whiskers and bring new insights into the oxidation behaviors of Cu on different crystal planes.
Milanova, Margarita; Aleksandrov, Lyubomir; Yordanova, Aneliya; Iordanova, R.; Tagiara, Nagia S.; Herrmann, Andreas; Gao, G.; Wondraczek, Lothar; Kamitsos, Efstratios I.
Structural and luminescence behavior of Eu3+ ions in ZnO-B2O3-WO3 glasses. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 600 (2023), 122006

Structure and luminescence properties of glasses with compositions 50ZnO:40B2O3:10WO3:xEu2O3, 0 ≤ x ≤ 10 mol% were studied using infrared, Raman and photoluminescence spectroscopic techniques. Physical properties like density, molar volume, oxygen molar volume and oxygen packing density of the glasses were also determined. The overall results obtained indicate the efficiency of the 50ZnO:40B2O3:10WO3 glass structure for the luminescence performance of doped Eu3+. The most intense luminescence peak observed at 612 nm and the high integrated emission intensity ratio (R) of the 5D0&flech;7F2/5D0&flech;7F1 transitions at 612 and 590 nm of 5.77 suggest that the glasses are potential materials for red emission. The results are compared to measurements of a glass without WO3 addition (50ZnO:50B2O3:5Eu2O3) and results from other publications of similar glasses.
Großmann, Max; Bohm, Sebastian; Heyder, Stefan; Schwarzburg, Klaus; Kleinschmidt, Peter; Runge, Erich; Hannappel, Thomas
Generalized modeling of photoluminescence transients. - In: Physica status solidi, ISSN 1521-3951, Bd. 260 (2023), 1, 2200339, S. 1-12

Time-resolved photoluminescence (TRPL) measurements and the extraction of meaningful parameters involve four key ingredients: a suitable sample such as a semiconductor double heterostructure, a state-of-the-art measurement setup, a kinetic model appropriate for the description of the sample behavior, and a general analysis method to extract the model parameters of interest from the measured TRPL transients. Until now, the last ingredient is limited to single curve fits, which are mostly based on simple models and least-squares fits. These are often insufficient for the parameter extraction in real-world applications. The goal of this article is to give the community a universal method for the analysis of TRPL measurements, which accounts for the Poisson distribution of photon counting events. The method can be used to fit multiple TRPL transients simultaneously using general kinematic models, but should also be used for single transient fits. To demonstrate this approach, multiple TRPL transients of a GaAs/AlGaAs heterostructure are fitted simultaneously using coupled rate equations. It is shown that the simultaneous fits of several TRPL traces supplemented by systematic error estimations allow for a more meaningful and more robust parameter determination. The statistical methods also quantify the quality of the description by the underlying physical model.
Schlag, Leslie; Isaac, Nishchay Angel; Hossain, Mohammad M.; Hess, Anna-Lena; Wolz, Benedikt C.; Reiprich, Johannes; Ziegler, Mario; Pezoldt, Jörg; Jacobs, Heiko O.
Self-aligning metallic vertical interconnect access formation through microlensing gas phase electrodeposition controlling airgap and morphology. - In: Advanced electronic materials, ISSN 2199-160X, Bd. 9 (2023), 1, 2200838, S. 1-8

This publication reports self-aligning metallic via microlensing gas phase electrodeposition formation. Key operational parameters to fabricate vertical ruthenium and rhodium interconnects (via) with a diameter of 100 nm are discussed. Moreover, airgaps are implemented during the deposition process, which utilizes spark discharge to generate a flux of charged nanoparticles. An inert gas flow transports the nanoparticles through a reactor chamber close to the target substrate. The substrate uses a pre-patterned resist with openings to a silicon/silicon dioxide/metal stack to direct the deposition of the nanoparticles to form localized self-aligning vertical interconnects. Five process parameters were identified, which impact the morphology and conductance of the resulting interconnects: spark discharge power, gas flow rate, microlens via dimensions, substrate surface potential, and in situ flash lamp power. This parameter set enables a controlled adjustment of the via interconnect morphology and its minimum feature size. Gas flow rate in combination with spark discharge power contribute significantly to the morphology of the interconnect. Spark power and microlens via dimensions have the largest influence on the surface potential of the insulating resist cover, which enables a localized microlensing gas phase electrodeposition of a via with a controlled ratio between conducting diameter and airgap.
Link, Steffen; Dimitrova, Anna; Krischok, Stefan; Ivanov, Svetlozar
Electrochemical deposition of silicon in organic electrolytes. - In: Reference module in chemistry, molecular sciences and chemical engineering, (2023)

Electrodeposition is a versatile instrumental technique, already applied in many industrial fields. However, the deposition of silicon and other reactive elements is still challenging and requires further research and improvement. Accomplishing an efficient electrodeposition of silicon at room temperature is very attractive due to the high number of manufacturing technologies that would benefit from this approach. This work provides an overview of the electrochemical approaches for silicon deposition performed in organic electrolytes. The main factors that impact this process are individually discussed and exemplified with appropriately updated literature sources. Furthermore, the previously available research on characterization of electrodeposited silicon containing layers is provided. These studies are presented in the context of better understanding the structure, composition, and functional properties of the deposited silicon material, which may attract the attention of young academic scientists and process engineers.
Gholami-Kermanshahi, Mozhgan; Wu, Yu-Yan; Lange, Günther; Chang, Shih-Hang
Effect of alloying elements (Nb, Ag) on the damping performance of Cu-Al-Mn shape memory alloys. - In: Journal of alloys and compounds, Bd. 930 (2023), 167438, S. 1-11

This study investigates the damping properties of Cu-Al-Mn shape memory alloys (SMAs) with various chemical compositions and the effects of the addition of quaternary alloying elements Ag and Nb on the microstructure, martensitic transformation behavior, and damping capacity of SMAs. Compared to other Cu-12Al-xMn (x = 4-7wt. %) SMAs, Cu-12Al-5Mn has a more significant inherent and intrinsic internal friction (IFPT + IFI) peak above room temperature. The addition of Ag or Nb to Cu-12Al-5Mn reduced the grain size, thereby increasing the hardness of the alloys; however, the damping capacity and temperature of the IFPT + IFI peak decreased simultaneously. The addition of Ag to Cu-12Al-5Mn significantly reduced the damping capacity (IFPT+IFI peak) because of the notable decrease in the amount of transformed martensite. Moreover, the addition of Nb to Cu-12Al-5Mn caused the AlNb3 phase to precipitate, limiting the mobility of the martensite variant interfaces and slightly decreasing the damping capacity (IFPT + IFI peak). Among the Ag- and Nb-doped Cu-12Al-5Mn SMAs, Cu-12Al-5Mn-1Nb showed not only a significantly higher hardness but also a higher IFPT + IFI peak, with tan δ exceeding 0.01 at approximately 50 &ring;C.
Mayer, Hannes; Tomaschko, Silvia; Mayer, Thomas; Lange, Günther
New method for evaluating and optimizing transient piston friction and cooling using a high-power laser in motored operation. - In: SAE International journal of engines, ISSN 1946-3944, Bd. 16 (2023), 4, 03-16-04-0025

The input of combustion heat in engines has a major impact on the piston friction and the resulting wear of the piston skirt. The new methodology presented here enables the simulation of combustion heat input during motored operation, and thus a detailed investigation of the piston friction under realistic piston temperature profiles of real engine operation is possible. For this purpose a standardized engine test bench for motored friction evaluations was expanded to include, among other things, a movable high-power diode laser with special defocusing optics. The setup of the test engine is based on the FEV teardown step methodology [1] and has open access to the engine piston from above due to a cylinder head dummy. Thus, the heat input by means of a high-power diode laser into the piston crown can be made. The reduced engine structure also enables a precise and highly accurate evaluation of the piston friction. A previously conducted validation process of the methodology ensures the most accurate possible replication of fired piston temperature profiles. The comparison between the piston temperatures measured in fired operation and those simulated in motored operation for a partial load operating point shows a maximum variance deviation of only 15&ring;C depending on the measuring point. The new methodology is also used in particular for the evaluation and detection of critical piston friction conditions. Experiments in this context are presented and discussed exemplary by using three measurement series at different operating temperatures and engine speeds. There is a gradual increase in the laser power for each series of measurements and thus in the heat input into the piston. The increase in heat input leads to a significant increase in friction at all operating points due to thermal expansion and the associated decrease reduction in piston clearance. Depending on the operating temperature and the engine speed, a critical piston friction condition is achieved and detected by the level of friction increase. The additional use of ultrasonic sensors and the knock sensor installed as standard makes a simultaneous measurement of the structure-borne sound signals possible. The increase in the acceleration levels of all sensors correlates here with the increase in piston friction. An evaluation of the noise, vibration, and harshness (NVH) measurement in both the frequency range and the crank angle (CA) range shows conspicuous high-frequency excitation levels that occur in the top dead center area. This correlation can be proven for all three measurement series. The results obtained here may open a path to an improved piston cooling strategy in the future.