@article{66036,
abstract = {{Light-assisted metal oxide-based chemiresistive gas sensors are widely explored for operation at relatively low temperatures, yet the investigation of the role of irradiance, as opposed to wavelength, remains underrepresented. Here, we systematically quantify the irradiance-dependent behavior of ordered mesoporous In2O3 under visible light illumination. Photoconductivity measurements reveal two distinct irradiance regimes consistent with trap-limited transport at low power and recombination- or saturation-limited transport at high power. Gas sensing experiments towards CO and H2 show a pronounced non-monotonic response, reaching maximum responses of 0.74 for 135 ppm CO at 67 mW cm−2 and 0.64 for 90 ppm H2 at 11 mW cm−2, followed by strong suppression at higher irradiance. Illumination also accelerated the response kinetics. At 60 ppm, t90 decreases from 96 to 12 s for CO and 141 to 27 s for H2, corresponding to an 8- and 5-fold faster response time, respectively. Near-ambient pressure-XPS under controlled atmosphere and density functional theory calculations indicate defect-mediated excitation. Oxygen vacancy states and illumination-induced modification of surface oxygen species govern this behavior. The results establish irradiance as a critical mechanistic parameter that determines whether In2O3 operates in a surface-controlled or bulk photoconductive regime. These findings highlight the need to explicitly optimize and report irradiance in illuminated gas sensor studies, and not only the power consumption of the light source.}},
author = {{Voth, Sven and Zhao, Zhenyu and Baier, Dominik and Glass, Alexandra and Elgabarty, Hossam and Sandberg, Oskar J. and Grundmeier, Guido and Tiemann, Michael and Smått, Jan-Henrik and Anttu, Nicklas and de los Arcos, Teresa and Weinberger, Christian}},
issn = {{2379-3694}},
journal = {{ACS Sensors}},
keywords = {{resistive gas sensing, indium oxide, photoactivation, irradiance, photoconductivity, charge carrier dynamics, oxygen vacancies}},
number = {{7}},
publisher = {{American Chemical Society (ACS)}},
title = {{{Role of Irradiance in Light-Activated In2O3Gas Sensors: Why More Light Is Not Always Better}}},
doi = {{10.1021/acssensors.6c01100}},
volume = {{11}},
year = {{2026}},
}
@article{63830,
abstract = {{ This study investigates the effect of dispersion gas (DG) flow on the formation and properties of maghemite (γ-Fe2O3) nanoparticles using standardized SpraySyn burners (SS1 and SS2). Several diagnostics were employed to characterize the spray and nanoparticles.
Increasing DG flow (6 - 12 slm) results in smaller droplet sizes (DS), cooler flame temperatures, shorter high-temperature droplet/particle residence times, and smaller agglomerates in the size range of 5 - 12 nm with narrower primary particle size distribution, corresponding to higher mass fractal dimensions, as supported by TEM and SMPS analysis, resulting in more compact agglomerates. BET and TEM confirmed decreasing primary particle sizes with increasing DG flow. Raman and XRD analyses predominantly identified maghemite, which shows a bimodal distribution of crystallite sizes, while SS1 samples have a greater proportion of larger crystallites.
The self-preserving size distributions of agglomerates with a geometric standard deviation of 1.5 are reached faster with increasing DG flow. The barrier effect of DG observed in SS1 leads to slower droplet combustion kinetics, higher temperatures, and delayed precursor release, which, along with downstream flow recirculation, result in significantly higher agglomeration rates outside the visible flame. SS2 demonstrates improved atomization, more stable flames, and finer, uniform nanoparticles with less carbonaceous residues (CR). Conversely, SS1 showed broader DS distributions and higher CR levels on the γ-Fe2O3 surface, especially at higher DG flow.
This work highlights the essential role of DG flow and nozzle geometry in controlling droplet evaporation, flame stability, and nanoparticle growth, offering insights for optimizing SFS and validating numerical models.
}},
author = {{Massopo, Orlando and Tischendorf, Ricardo and Gonchikzhapov, Munko and Kasper, Tina and Augustin, Peter and Özer, Burak and Reddemann, Manuel and Kneer, Reinhold and Sheikh, Mohammed-Ali and Mert, Aydan Akyildiz and Wiggers, Hartmut and Schmid, Hans-Joachim}},
issn = {{0032-5910}},
journal = {{Powder Technology}},
keywords = {{Spray flame synthesis, iron oxide nanoparticle, SpraySyn burner, Dispersion gas, Coaxial atomization, HiaT-SMPS}},
publisher = {{Elsevier BV}},
title = {{{Influence of dispersion gas flow on the spray characteristics and γ-Fe2O3 nanoparticles formation and properties in reference SpraySyn burners}}},
doi = {{10.1016/j.powtec.2025.121992}},
volume = {{470}},
year = {{2025}},
}
@inproceedings{64798,
abstract = {{Lead-containing piezoelectric ceramics are still the base for today’s ultrasonic transducers used in broad applications. This is partly due to missing powerful lead-free piezoelectric ceramic parts in the commercial market. There has been much research on lead-free materials but developing them into marketable parts seems to be an ongoing process. The actual exemption of ROHS has expired, but as the new exemption has already been requested, ceramic suppliers keep on selling lead containing products. Nevertheless, these should be replaced by lead-free alternatives for environmental and health issues.
This contribution focuses on exploring the technological readiness level of lead-free hard piezoceramics for prestressed ultrasonic transducers. A small series of bolted Langevin transducers was set up with standard PZT material and three commercial lead-free variants. Results of the building process from individual ring ceramic characteristics to transducer load tests are presented. The main finding of this study is that the lead-free materials technically can compete with the standard PZT for medium-power applications. Some adaptations in the ultrasonic system must be done: the geometry must be altered to fit resonance frequency, and higher voltages or thinner ceramics are needed to achieve the same vibration level at low load. For reaching same power, the volume of lead-free ceramics must be 1.5 to 3 times larger. As already promoted in literature, mechanical losses at high vibration levels are smaller for the lead-free materials. This might help to argument lead-free piezoelectric materials in some applications.
References
1. Directive 2011/65/EU of the European Parliament and of the Council of 8 June 2011 on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment. EUR-Lex Document 02011L0065-20240801. Available online: http://data.europa.eu/eli/dir/2011/65/2024-08-01 (accessed on 24 January 2025).
2. Langevin, P. (1918) Method and Apparatus for Transmitting and Receiving Submarine Elastic Waves Using the Piezoelectric Properties of Quartz. French Patent Office; Patent No. FR505703.
3. Hemsel, T.; Twiefel, J. (2023) Piezoelectric Ultrasonic Power Transducers. In Encyclopedia of Materials: Electronics; Academic Press: Oxford, UK; pp. 276–285. https://doi.org/10.1016/b978-0-12-819728-8.00047-4.
4. ATHENA Technologie Beratung GmbH (2025) Description of Ultrasound Generator. Available online: http://shop.myathena.de/epages/12074748.sf/de_DE/?ObjectPath=/Shops/12074748/Products/AM200 (accessed on 13 January 2025).
5. Littmann, W.; Hemsel, T.; Kauczor, C.; Wallaschek, J.; Sinha, W. (2003) Load-adaptive phase-controller for resonant driven piezoelectric devices. Proc. World Congr. Ultrason. 2003, 48, 547–550.
6. Scheidemann, C., Bornmann, P., Littmann, W., & Hemsel, T. (2025). Lead-Free Ceramics in Prestressed Ultrasonic Transducers. Actuators, 14(2), 55. https://doi.org/10.3390/act14020055
}},
author = {{Scheidemann, Claus and Bornmann, Peter and Littmann, Walter and Hemsel, Tobias}},
keywords = {{lead free piezoelectric ceramics, bolted Langevin transducer, medium power ultrasound.}},
location = {{Vilnius, Lithuania}},
title = {{{Bolted Langevin transducers with leadfree piezoelectric ceramics}}},
year = {{2025}},
}
@article{62643,
author = {{Schwabe, Tobias and Kress, Christian and Kruse, Stephan and Weizel, Maxim and Rhee, Hanjo and Scheytt, J. Christoph}},
journal = {{Journal of Lightwave Technology}},
keywords = {{Integrated circuit modeling, Capacitance, Silicon, Modulation, Adaptation models, Semiconductor device modeling, Bandwidth, Data communication, electrooptical transmitter, equalization, free-carrier-plasma dispersion effect, modelling, optical modulator, phase shifter, silicon photonics}},
number = {{1}},
pages = {{255--270}},
title = {{{Forward-Biased Silicon Phase Shifter Modeling for Electronic-Photonic Co-Simulation and Validation in a 250 nm EPIC BiCMOS Technology}}},
doi = {{10.1109/JLT.2024.3450949}},
volume = {{43}},
year = {{2025}},
}
@article{62644,
author = {{Schwabe, Tobias and Kress, Christian and Sadiye, Babak and Kruse, Stephan and Scheytt, J. Christoph}},
journal = {{IEEE Access}},
keywords = {{Optical attenuators, Equalizers, Phase shifters, Optical modulation, Electro-optic modulators, Optical amplifiers, Circuits, Silicon photonics, Optical saturation, Integrated circuit modeling, Data communication, equalization, electro-optical transmitter, silicon photonics, phase shifter, optical modulator, free-carrier plasma dispersion effect, driver architectures, biasing schemes}},
pages = {{192433--192450}},
title = {{{Analysis and Design of Forward Biased Silicon Photonics Phase Shifter Equalizer Circuits}}},
doi = {{10.1109/ACCESS.2025.3629385}},
volume = {{13}},
year = {{2025}},
}
@article{55999,
abstract = {{Clean hydrogen is a key aspect of carbon neutrality, necessitating robust methods for monitoring hydrogen concentration in critical infrastructures like pipelines or power plants. While semiconducting metal oxides such as In2O3 can monitor gas concentrations down to the ppm range, they often exhibit cross-sensitivity to other gases like H2O. In this study, we investigated whether cyclic optical illumination of a gas-sensitive In2O3 layer creates identifiable changes in a gas sensor´s electronic resistance that can be linked to H2 and H2O concentrations via machine learning. We exposed nanostructured In2O3 with a large surface area of 95 m2 g-1 to H2 concentrations (0-800 ppm) and relative humidity (0-70%) under cyclic activation utilizing blue light. The sensors were tested for 20 classes of gas combinations. A support vector machine achieved classification rates up to 92.0%, with reliable reproducibility (88.2 ± 2.7%) across five individual sensors using 10-fold cross-validation. Our findings suggest that cyclic optical activation can be used as a tool to classify H2 and H2O concentrations.}},
author = {{Baier, Dominik and Krüger, Alexander and Wagner, Thorsten and Tiemann, Michael and Weinberger, Christian}},
issn = {{2227-9040}},
journal = {{Chemosensors}},
keywords = {{resistive gas sensor, chemiresistor, semiconductor, metal oxide, In2O3, mesoporous, hydrogen, humidtiy, machine learning, sustainable}},
number = {{9}},
pages = {{178}},
publisher = {{MDPI}},
title = {{{Gas Sensing with Nanoporous In2O3 under Cyclic Optical Activation: Machine Learning-Aided Classification of H2 and H2O}}},
doi = {{10.3390/chemosensors12090178}},
volume = {{12}},
year = {{2024}},
}
@misc{51136,
abstract = {{Iron oxide nanoparticles are very interesting for many applications in different industrial sectors. A promising
process to manufacture these nanoparticles is flame spray pyrolysis (FSP). A lack of understanding of the
individual sub-processes in FSP makes it challenging to tailor nanoparticle properties. This work provides
insights into the formation of iron oxide nanoparticles in a turbulent spray flame using Large Eddy Simulations
(LES), which are based on a comprehensive model, including customized submodels. Highlights are the
adaption of a turbulent combustion model and a bivariate hybrid method of moments for modeling nanoparticle
dynamics. The work focuses on the SpraySyn burner, which is a standardized laboratory burner and was
operated with a precursor-solvent mixture of ethanol and iron(III) nitrate nonahydrate. For studying the
relevance of precursor chemistry, LES using an evaporation-limited precursor chemistry model is compared
with a model that includes detailed iron chemistry. A further novelty is the inclusion of adsorption in the
simulation, which defines a third model for comparison. Sufficient validation is achieved for the undoped LES
using experimental data from the literature. A strong impact of the detailed iron chemistry and adsorption
is found on the precursor consumption and the aggregate and primary particle formation. Comparing the
particle diameters with experimental measurements from the literature and data generated for this work is
found unsuitable to asses the precursor chemistry model and revealed an urgent need for future experimental
and numerical research. This work serves as a step forward in realizing a reliable model.}},
booktitle = {{Applications in Energy and Combustion Science}},
editor = {{Fröde, Fabian and Grenga, Temistocle and Pitsch, Heinz and Dupont, Sophie and Kneer, Reinhold and Tischendorf, Ricardo and Massopo, Orlando and Schmid, Hans-Joachim}},
keywords = {{Flame spray pyrolysis, Iron oxide formation, Large eddy simulation, Method of moments, SpraySyn}},
publisher = {{Elsevier}},
title = {{{Large eddy simulation of iron oxide formation in a laboratory spray flame}}},
doi = {{https://doi.org/10.1016/j.jaecs.2023.100191}},
year = {{2023}},
}
@article{30917,
abstract = {{We study lobby group formation in a two-stage model where the players rst form lobby
groups that then engage in a rent-seeking contest to in uence the legislator. However, the
outcome of the contest aects all players according to the ideological distance between the
implemented policy and the players' preferences. The players can either lobby by themselves,
form a coalition of lobbyists or free ride. We nd that free coalition formation is reasonable
if either players with moderate preferences face lobby groups with extreme preferences, or if
there are two opposing coalitions with an equal number of members. Otherwise, there are
always free riders among the players.}},
author = {{Block, Lukas}},
journal = {{Quick And Easy Journal Title}},
keywords = {{Group formation, Rent-seeking, Free riding}},
title = {{{Coalition formation versus free riding in rent-seeking contests}}},
year = {{2022}},
}
@inproceedings{29803,
abstract = {{Ultrasonic wire bonding is a solid-state joining process used to form electrical interconnections in micro and
power electronics and batteries. A high frequency oscillation causes a metallurgical bond deformation in
the contact area. Due to the numerous physical influencing factors, it is very difficult to accurately capture
this process in a model. Therefore, our goal is to determine a suitable feed-forward control strategy for the
bonding process even without detailed model knowledge. We propose the use of batch constrained Bayesian
optimization for the control design. Hence, Bayesian optimization is precisely adapted to the application of
bonding: the constraint is used to check one quality feature of the process and the use of batches leads to
more efficient experiments. Our approach is suitable to determine a feed-forward control for the bonding
process that provides very high quality bonds without using a physical model. We also show that the quality
of the Bayesian optimization based control outperforms random search as well as manual search by a user.
Using a simple prior knowledge model derived from data further improves the quality of the connection.
The Bayesian optimization approach offers the possibility to perform a sensitivity analysis of the control
parameters, which allows to evaluate the influence of each control parameter on the bond quality. In summary,
Bayesian optimization applied to the bonding process provides an excellent opportunity to develop a feedforward
control without full modeling of the underlying physical processes.}},
author = {{Hesse, Michael and Hunstig, Matthias and Timmermann, Julia and Trächtler, Ansgar}},
booktitle = {{Proceedings of the 11th International Conference on Pattern Recognition Applications and Methods (ICPRAM)}},
isbn = {{978-989-758-549-4}},
keywords = {{Bayesian optimization, Wire bonding, Feed-forward control, model-free design}},
location = {{Online}},
pages = {{383--394}},
title = {{{Batch Constrained Bayesian Optimization for UltrasonicWire Bonding Feed-forward Control Design}}},
year = {{2022}},
}
@article{62813,
abstract = {{Nanostructured manganese oxides have a rich variety of morphologies and crystal phases which can undergo transformations during synthesis and application. Although these structural features are crucial for their performance, the mechanisms behind such transitions are not well understood. Herein, we describe the mechanism of transformation from layered 2D δ-MnO2 nanosheets to the scarcely reported γ-MnO2 nanocone morphology. Despite the common purpose of introducing Fe dopants to enhance the conductivity of layered manganese oxides, the Fe galvanic exchange reaction was found responsible for such coupled phase/morphology transition. Electrochemical characterization confirmed a distinct electrochemical behaviour of the nanocones, emphasizing the need to unravel the mechanism of 2D MnO2 transformation. Such mechanistic insights were gained by systematic and rigorous electron microscopy studies. The effect of the local chemical composition was determined by energy dispersive X-ray spectroscopy while electron energy loss spectroscopy unravelled the key influence of the oxidation state of Mn ions within nanosheets and nanocones. We propose and demonstrate a Mn2+-mediated oxidative mechanism of coupled morphology/phase transformation subjected to the equilibrium of Fe and Mn ions during galvanic exchange reaction. These findings contribute to the understanding of the growth and morphology/phase transformations of manganese oxide nanostructures, providing insights for the rational design of nanomaterials.}},
author = {{Aymerich-Armengol, Raquel and Cignoni, Paolo and Ebbinghaus, Petra and Linnemann, Julia and Rabe, Martin and Tschulik, Kristina and Scheu, Christina and Lim, Joohyun}},
issn = {{2050-7488}},
journal = {{Journal of Materials Chemistry A}},
keywords = {{manganese oxide, nanomaterials, TEM, supercapacitors}},
number = {{45}},
pages = {{24190--24198}},
publisher = {{Royal Society of Chemistry (RSC)}},
title = {{{Mechanism of coupled phase/morphology transformation of 2D manganese oxides through Fe galvanic exchange reaction}}},
doi = {{10.1039/d2ta06552e}},
volume = {{10}},
year = {{2022}},
}
@article{25212,
abstract = {{Finding a good query plan is key to the optimization of query runtime. This holds in particular for cost-based federation
engines, which make use of cardinality estimations to achieve this goal. A number of studies compare SPARQL federation engines across different performance metrics, including query runtime, result set completeness and correctness, number of sources selected and number of requests sent. Albeit informative, these metrics are generic and unable to quantify and evaluate the accuracy of the cardinality estimators of cost-based federation engines. To thoroughly evaluate cost-based federation engines, the effect of estimated cardinality errors on the overall query runtime performance must be measured. In this paper, we address this challenge by presenting novel evaluation metrics targeted at a fine-grained benchmarking of cost-based federated SPARQL query engines. We evaluate five cost-based federated SPARQL query engines using existing as well as novel evaluation metrics by using LargeRDFBench queries. Our results provide a detailed analysis of the experimental outcomes that reveal novel insights, useful for the development of future cost-based federated SPARQL query processing engines.}},
author = {{Qudus, Umair and Saleem, Muhammad and Ngonga Ngomo, Axel-Cyrille and Lee, Young-Koo}},
issn = {{2210-4968}},
journal = {{Semantic Web}},
keywords = {{SPARQL, benchmarking, cost-based, cost-free, federated, querying}},
number = {{6}},
pages = {{843--868}},
publisher = {{ISO Press}},
title = {{{An Empirical Evaluation of Cost-based Federated SPARQL Query Processing Engines}}},
doi = {{10.3233/SW-200420}},
volume = {{12}},
year = {{2021}},
}
@article{64018,
abstract = {{CO oxidation is an extensively studied reaction in heterogeneous catalysis due to its seeming simplicity and its great importance for emission control. However, the role of particle size and more specifically structure sensitivity in this reaction is still controversial. In the present study, colloidal “surfactant-free” Pt nanoparticles (NPs) in a size regime of 1–4 nm with narrow size distribution and control over particle size were synthesized and subsequently supported on Al2O3 to prepare model catalysts. CO oxidation was performed using Pt NPs catalysts with particles sizes of 1, 2, 3, and 4 nm at different reaction temperatures. It is shown that the reaction exhibits a particle size effect that depends strongly on the reaction conditions. At 170 °C, the reaction seems to proceed within the same kinetic regime for all particle sizes, but the surface normalized activity depends strongly on the particle size, with maximum activity for nanoparticles 2 nm in diameter. A temperature increase to 200 °C leads to a change of the kinetic regime that depends on the particle size. For Pt NPs 1 nm in diameter a reaction order of 1 for O2 was observed, indicating that O2 adsorbs molecularly and dissociates in a following step, which represents the generally accepted mechanism on Pt surfaces. The reaction order of −1 for CO demonstrates that the surface is saturated with CO under reaction conditions. With increasing particle size, the reaction orders of O2 and CO change. For particles 2 nm in size, an increase in temperature also results in reaction orders of 1 for O2 and −1 for CO; NPs of 3 and 4 nm, even at higher temperatures, show no clear kinetic behavior that can be explained by a single reaction mechanism. Instead, the Boudouard reaction between two adjacent adsorbed CO molecules was identified as an important additional reaction pathway that occurs preferentially on large particles and causes more complex kinetics.}},
author = {{Neumann, Sarah and Gutmann, Torsten and Buntkowsky, Gerd and Paul, Stephen and Thiele, Greg and Sievers, Heiko and Bäumer, Marcus and Kunz, Sebastian}},
journal = {{Journal of Catalysis}},
keywords = {{Solid state NMR, “Surfactant-free” platinum nanoparticles, CO oxidation, Particle size effect, Structure sensitivity}},
pages = {{662–672}},
title = {{{Insights into the reaction mechanism and particle size effects of CO oxidation over supported Pt nanoparticle catalysts}}},
doi = {{10.1016/j.jcat.2019.07.049}},
volume = {{377}},
year = {{2019}},
}
@inproceedings{59220,
author = {{Schwabe, Tobias and Balke, Axel and Bezuidenhout, Petrone H. and Reker, Julia and Meyers, Thorsten and Joubert, Trudi-Heleen and Hilleringmann, Ulrich}},
booktitle = {{Fifth Conference on Sensors, MEMS, and Electro-Optic Systems}},
editor = {{du Plessis, Monuko}},
keywords = {{sensing, zinc oxide, thin-film transistor, oxygen measurement, low-cost electronics, water quality analysis, printable electronics, flexible electronics}},
pages = {{1104316}},
publisher = {{SPIE}},
title = {{{Oxygen detection with zinc oxide nanoparticle structures}}},
doi = {{10.1117/12.2501507}},
volume = {{11043}},
year = {{2019}},
}
@article{4947,
abstract = {{Manufacturers increasingly integrate information and communication technologies into their products so that they can provide IT-based services. Organizations that formerly concentrated on transactional sales thus confront a new challenge associated with managing service usage—retention and extracting value from investments in smart technology. This study combines a marketing and an information systems perspective in a field study conducted jointly with a large European car manufacturer. Understanding the renewal decision for IT-based service contracts requires knowledge from both disciplines. The paper shows that combining behavioral predictor variables stemming from marketing research and technology-related perceptual variables stemming from technology acceptance research increases the explanatory power and prediction accuracy of forecasting models for customer renewal decisions. Specifically, the authors show that perceptions of usefulness become more important the longer customers use IT-based services and the more services they use within the service contract.}},
author = {{Wangenheim, Florian v and Wünderlich, Nancy and Schumann, Jan H}},
journal = {{Journal of Business Research}},
keywords = {{IT-based service, Smart services, Contract renewal, Retention, Customer churn, Free trial}},
number = {{79}},
pages = {{181----188}},
publisher = {{Elsevier}},
title = {{{Renew or cancel? Drivers of customer renewal decisions for IT-based service contracts}}},
year = {{2017}},
}
@article{13187,
abstract = {{Abstract The reaction of Cu(I) bisguanidine complexes with nitric oxide and the formation of intermediate species were monitored via UV-vis spectroscopy at low temperature, with the occurrence of characteristic absorption bands. The origin of the emerging species and their character were substantiated by electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) studies showing a delocalized {CuNO}11 radical species. Furthermore, this system was transferred to the SuperFocus mixer setup, which allows rapid mixing and the determination of decay constants at ambient temperatures of the thermally sensitive species. However, these experiments demonstrated the limits of these systems, such as the NO saturation in organic solvents and a preferably precise temperature control within the SuperFocus mixer, which should be addressed in the future.}},
author = {{Oppermann, Alexander and Laurini, Larissa and Etscheidt, Fabian and Hollmann, Katharina and Strassl, Florian and Hoffmann, Alexander and Schurr, Daniela and Dittmeyer, Roland and Rinke, Günter and Herres-Pawlis, Sonja}},
journal = {{Chemical Engineering \& Technology}},
keywords = {{Copper guanidine complexes, Nitric oxide, SuperFocus mixer}},
number = {{8}},
pages = {{1475--1483}},
title = {{{Detection of Copper Bisguanidine NO Adducts by UV-vis Spectroscopy and a SuperFocus Mixer}}},
doi = {{10.1002/ceat.201600691}},
volume = {{40}},
year = {{2017}},
}
@inproceedings{9959,
abstract = {{Ultrasonic heavy wire bonding is a commonly used technology to conduct electrical devices in power electronics. In order to facilitate powerful solutions combined with an increased efficiency, involving a material change from aluminum to copper wire as conductor material takes place in recent years. Due to the material related properties, copper wire bonding requires significant higher bond processing parameters such as bond force and ultrasonic power compared to aluminum which can lead to damages or a failure of the bonded component. Therefore, a profound knowledge of the processes prevailing during wire bonding is essential to optimize the application of the copper wires and consequently to achieve the demands on quality and reliability. The behavior of different natural surface oxides of aluminum and copper are assumed to be one reason for the deviation in the required bond parameters. Accordingly, the impact of differently pre-treated substrates surfaces on which the bonding is applied were investigated in this study. First, all conditions investigated (as-received, oxidefree, AlOx and the CuOx) were characterized by utilizing scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam microscopy and atomic force microscopy. In addition, hardness tests were performed as well as perthometer measurements. Afterwards, a 500 $\mu$ m copper wire was bonded on the generated surfaces investigated. In consideration of the roughness, shear test of various bond times and microscopic images were evaluated. Finally, the results were compared and discussed. Overall, the current study indicates that an Al-oxide layer is beneficial for welding process in Cu wire bonding. On the contrary, the Cu-oxide is detrimental and leads to a delayed welding of the joining parts. Based on the obtained results, it can be expected that due to an ideal set of Al-oxide layers, lower optimal bond parameters can used to reach high bond strength with good reliability properties.}},
author = {{Eacock, Florian and Unger, Andreas and Eichwald, Paul and Grydin, Olexandr and Hengsbach, Florian and Althoff, Simon and Schaper, Mirko and Guth, Karsten}},
booktitle = {{IEEE 66th Electronic Components and Technology Conference}},
keywords = {{Ultrasonic copper wire bonding, Al-oxide, Cuoxide, oxide-free, roughness, morphology}},
pages = {{2111--2118}},
title = {{{Effect of different oxide layers on the ultrasonic copper wire bond process}}},
doi = {{10.1109/ECTC.2016.91}},
year = {{2016}},
}
@article{9878,
abstract = {{(K,Na)NbO3 ceramics have attracted much attention as lead-free piezoelectric materials with high piezoelectric properties. High-quality (K,Na)NbO3 ceramics can be sintered using KNbO3 and NaNbO3 powders synthesized by a hydrothermal method. In this study, to enhance the quality factor of the ceramics, high-power ultrasonic irradiation was employed during the hydrothermal method, which led to a reduction in the particle size of the resultant powders.}},
author = {{Isobe, G. and Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}},
issn = {{0885-3010}},
journal = {{Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on}},
keywords = {{Q-factor, ceramics, crystal growth from solution, particle size, piezoelectric materials, potassium compounds, powders, sintering, sodium compounds, ultrasonic effects, (K0.48Na0.52)NbO3, KNbO3 powders, NaNbO3 powders, high-power ultrasonic irradiation, lead-free piezoelectric materials, lead-free piezoelectric powders, particle size reduction, piezoelectric properties, quality factor, sintered (K0.48Na0.52)NbO3 ceramics, sintering, ultrasonic-assisted hydrothermal method, Acoustics, Ceramics, Lead, Piezoelectric materials, Powders, Radiation effects, Transducers}},
number = {{2}},
pages = {{225--230}},
title = {{{Synthesis of lead-free piezoelectric powders by ultrasonic-assisted hydrothermal method and properties of sintered (K0.48Na0.52)NBO3 ceramics}}},
doi = {{10.1109/TUFFC.2014.6722608}},
volume = {{61}},
year = {{2014}},
}
@inproceedings{9788,
abstract = {{A hydrothermal method utilizes a crystallization process in the solution so that the pure and high-quality powders can be realized. Sintering from the hydrothermal KNbO3 and NaNbO3 powders, a high-dense lead-free piezoelectric (K,Na)NbO3 ceramics could be obtained (density: 98.8\%). Concerning about the g33 constant, high value as large as commercial PZT ceramics was measured. Therefore, the hydrothermal (K,Na)NbO3 ceramics is usable for the sensors and the energy harvesting devices. To demonstrate the (K,Na)NbO3 ceramics, a hydrophone sensor was fabricated and evaluated.}},
author = {{Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}},
booktitle = {{Ultrasonics Symposium (IUS), 2012 IEEE International}},
issn = {{1948-5719}},
keywords = {{crystallisation, hydrophones, piezoceramics, potassium compounds, powder technology, powders, sensors, sintering, sodium compounds, (K0.48Na0.52)NbO3, KNbO3 powder, NaNbO3 powder, crystallization, energy harvesting devices, g33 constant, hydrophone sensor, hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics, hydrothermal method, piezoelectric applications, sintering, Materials, Transducers}},
pages = {{194--195}},
title = {{{Piezoelectric applications of hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics}}},
doi = {{10.1109/ULTSYM.2012.0048}},
year = {{2012}},
}
@article{9743,
abstract = {{The hydrothermal method enables the production of high-quality piezoelectric materials. In this study, we propose to irradiate the reaction solutions with ultrasonic power during the hydrothermal method to obtain a shorter reaction time and a smooth film surface. A high-pressure reaction container for the ultrasonic transducer was newly developed, and the ultrasonically-assisted hydrothermal method was examined by using this container. The effect of ultrasonic assist on the synthesis of lead-zirconate-titanate (PZT) thin films and (K,Na)NbO$_{3}$ powders was verified. Thicker PZT film, thickness around 10 ${\mu}$m, could be obtained in one process, and (K,Na)NbO$_{3}$ powder was synthesized in half the previous reaction time.}},
author = {{Ageba, Ryo and Kadota, Yoichi and Maeda, Takafumi and Takiguchi, Norihito and Morita, Takeshi and Ishikawa, Mutsuo and Bornmann, Peter and Hemsel, Tobias}},
issn = {{1948-5719}},
journal = {{Journal of Korean Physical Society}},
keywords = {{Hydrothermal method, High-power ultrasonic, PZT thin film, Lead-free piezoelectric materials}},
number = {{4}},
pages = {{918--923}},
title = {{{Ultrasonically-assisted Hydrothermal Method for Ferroelectric Material Synthesis}}},
doi = {{10.3938/jkps.57.918}},
volume = {{57}},
year = {{2010}},
}
@article{9758,
abstract = {{As a lead-free piezoelectric ceramics, (K,Na)NbO$_{3}$ is a promising material because of its good piezoelectric properties. In this study, (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics were synthesized from a KNbO$_{3}$ and NaNbO$_{3}$ mixture powder prepared by the hydrothermal reaction. The hydrothermal reaction enables the production of high quality powder for the ceramics fabrication process. To obtain (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics, these two powders KNbO$_{3}$ and NaNbO$_{3}$ were mixed and then sintered together. X-Ray diffraction analysis revealed that the solid solution ceramics (K$_{1-x}$Na$_{x}$)NbO$_{3}$ was produced by the sintering process. The K/Na ratio in (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics was optimized for the best piezoelectric properties. The optimized forms was (K$_{0.48}$Na$_{0.52}$)NbO$_{3}$, which showed the following piezoelectric properties; k$_{33}$=0.56, d$_{33}$=114pC/N. In addition, the ferroelectric properties, P$_{r}$=7.72mC/cm$^{2}$, E$_{c}$=857V/mm, and the Curie temperature T$_{c}$=420$_{o}$C were also measured.}},
author = {{Maeda, Takafumi and Takiguchi, Norihito and Morita, Takeshi and Ishikawa, Mutsuo and Hemsel, Tobias}},
issn = {{1948-5719}},
journal = {{Journal of Korean Physical Society}},
keywords = {{Lead-free piezoelectric material, KNN, Hydrothermal method}},
number = {{4}},
pages = {{924--928}},
title = {{{Hydrothermal (K1-xNax)NbO3 Lead-free Piezoelectric Ceramics}}},
doi = {{10.3938/jkps.57.924}},
volume = {{57}},
year = {{2010}},
}