@article{36414, abstract = {{ Recently, microcavities with anisotropic materials were shown to be able to create bands with non-zero local Berry curvature. The anisotropic refractive index of the cavity layer is believed to be critical in opening an energy gap at the tilted Dirac points. In this work, we show that the anticrossing between a cavity mode and a Bragg mode can also be realized within an empty microcavity without any birefringent materials in the cavity layer. Nondispersive bands are observed within the energy gap due to the particular refractive index distribution of the sample. The intrinsic TE-TM splitting and XY splitting of DBR mirrors induce the squeezing of the cavity modes in momentum space, so that the nondispersive bands are tilted and spin-dependent. Our results pave the way to investigate interesting physical phenomena of photonic modes close to or in the nondispersive bands without anisotropic cavity layers. }}, author = {{Gao, Ying and Li, Yao and Ma, Xuekai and Gao, Meini and Dai, Haitao and Schumacher, Stefan and Gao, Tingge}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{Physics and Astronomy (miscellaneous)}}, number = {{20}}, publisher = {{AIP Publishing}}, title = {{{Tilting nondispersive bands in an empty microcavity}}}, doi = {{10.1063/5.0093908}}, volume = {{121}}, year = {{2022}}, } @article{33671, abstract = {{Abstract We demonstrate the fabrication of micron-wide tungsten silicide superconducting nanowire single-photon detectors on a silicon substrate using laser lithography. We show saturated internal detection efficiencies with wire widths ranging from 0.59 µm to 1.43 µm under illumination at 1550 nm. We demonstrate both straight wires, as well as meandered structures. Single-photon sensitivity is shown in devices up to 4 mm in length. Laser-lithographically written devices allow for fast and easy structuring of large areas while maintaining a saturated internal efficiency for wire widths around 1 µm.}}, author = {{Protte, Maximilian and Verma, Varun B and Höpker, Jan Philipp and Mirin, Richard P and Woo Nam, Sae and Bartley, Tim}}, issn = {{0953-2048}}, journal = {{Superconductor Science and Technology}}, keywords = {{Materials Chemistry, Electrical and Electronic Engineering, Metals and Alloys, Condensed Matter Physics, Ceramics and Composites}}, number = {{5}}, publisher = {{IOP Publishing}}, title = {{{Laser-lithographically written micron-wide superconducting nanowire single-photon detectors}}}, doi = {{10.1088/1361-6668/ac5338}}, volume = {{35}}, year = {{2022}}, } @article{30342, author = {{Lange, Nina Amelie and Höpker, Jan Philipp and Ricken, Raimund and Quiring, Viktor and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}}, issn = {{2334-2536}}, journal = {{Optica}}, keywords = {{Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}}, number = {{1}}, publisher = {{The Optical Society}}, title = {{{Cryogenic integrated spontaneous parametric down-conversion}}}, doi = {{10.1364/optica.445576}}, volume = {{9}}, year = {{2022}}, } @article{33672, abstract = {{Abstract Lithium niobate is a promising platform for integrated quantum optics. In this platform, we aim to efficiently manipulate and detect quantum states by combining superconducting single photon detectors and modulators. The cryogenic operation of a superconducting single photon detector dictates the optimisation of the electro-optic modulators under the same operating conditions. To that end, we characterise a phase modulator, directional coupler, and polarisation converter at both ambient and cryogenic temperatures. The operation voltage V π / 2 of these modulators increases, due to the decrease in the electro-optic effect, by 74% for the phase modulator, 84% for the directional coupler and 35% for the polarisation converter below 8.5 K . The phase modulator preserves its broadband nature and modulates light in the characterised wavelength range. The unbiased bar state of the directional coupler changed by a wavelength shift of 85 n m while cooling the device down to 5 K . The polarisation converter uses periodic poling to phasematch the two orthogonal polarisations. The phasematched wavelength of the utilised poling changes by 112 n m when cooling to 5 K .}}, author = {{Thiele, Frederik and vom Bruch, Felix and Brockmeier, Julian and Protte, Maximilian and Hummel, Thomas and Ricken, Raimund and Quiring, Viktor and Lengeling, Sebastian and Herrmann, Harald and Eigner, Christof and Silberhorn, Christine and Bartley, Tim}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, keywords = {{Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}}, number = {{3}}, publisher = {{IOP Publishing}}, title = {{{Cryogenic electro-optic modulation in titanium in-diffused lithium niobate waveguides}}}, doi = {{10.1088/2515-7647/ac6c63}}, volume = {{4}}, year = {{2022}}, } @article{33673, abstract = {{ Superconducting Nanowire Single Photon Detectors (SNSPDs) have become an integral part of quantum optics in recent years because of their high performance in single photon detection. We present a method to replace the electrical input by supplying the required bias current via the photocurrent of a photodiode situated on the cold stage of the cryostat. Light is guided to the bias photodiode through an optical fiber, which enables a lower thermal conduction and galvanic isolation between room temperature and the cold stage. We show that an off-the-shelf InGaAs–InP photodiode exhibits a responsivity of at least 0.55 A/W at 0.8 K. Using this device to bias an SNSPD, we characterize the count rate dependent on the optical power incident on the photodiode. This configuration of the SNSPD and photodiode shows an expected plateau in the single photon count rate with an optical bias power on the photodiode above 6.8 µW. Furthermore, we compare the same detector under both optical and electrical bias, and show there is no significant changes in performance. This has the advantage of avoiding an electrical input cable, which reduces the latent heat load by a factor of 100 and, in principle, allows for low loss RF current supply at the cold stage. }}, author = {{Thiele, Frederik and Hummel, Thomas and Protte, Maximilian and Bartley, Tim}}, issn = {{2378-0967}}, journal = {{APL Photonics}}, keywords = {{Computer Networks and Communications, Atomic and Molecular Physics, and Optics}}, number = {{8}}, publisher = {{AIP Publishing}}, title = {{{Opto-electronic bias of a superconducting nanowire single photon detector using a cryogenic photodiode}}}, doi = {{10.1063/5.0097506}}, volume = {{7}}, year = {{2022}}, } @article{47984, abstract = {{Recent analyses by polarization resolved second-harmonic (SH) microscopy have demonstrated that ferroelectric (FE) domain walls (DWs) can possess non-Ising wall characteristics and topological nature. These analyses rely on locally analyzing the properties, directionality, and magnitude of the second-order nonlinear tensor. However, when inspecting FE DWs with SH microscopy, a manifold of different effects may contribute to the observed signal difference between domains and DWs, i.e., far-field interference, Čerenkov-type phase-matching (CSHG), and changes in the aforementioned local nonlinear optical properties. They all might be present at the same time and, therefore, require careful interpretation and separation. In this work, we demonstrate how the particularly strong Čerenkov-type contrast can selectively be blocked using dark- and bright-field SH microscopy. Based on this approach, we show that other contrast mechanisms emerge that were previously overlayed by CSHG but can now be readily selected through the appropriate experimental geometry. Using the methods presented, we show that the strength of the CSHG contrast compared to the other mechanisms is approximately 22 times higher. This work lays the foundation for the in-depth analysis of FE DW topologies by SH microscopy.}}, author = {{Hegarty, Peter A. and Beccard, Henrik and Eng, Lukas M. and Rüsing, Michael}}, issn = {{0021-8979}}, journal = {{Journal of Applied Physics}}, keywords = {{General Physics and Astronomy}}, number = {{24}}, publisher = {{AIP Publishing}}, title = {{{Turn all the lights off: Bright- and dark-field second-harmonic microscopy to select contrast mechanisms for ferroelectric domain walls}}}, doi = {{10.1063/5.0094988}}, volume = {{131}}, year = {{2022}}, } @article{47982, abstract = {{Spontaneous Raman spectroscopy (SR) is a versatile method for analysis and visualization of ferroelectric crystal structures, including domain walls. Nevertheless, the necessary acquisition time makes SR impractical for in situ analysis and large scale imaging. In this work, we introduce broadband coherent anti-Stokes Raman spectroscopy (B-CARS) as a high-speed alternative to conventional Raman techniques and demonstrate its benefits for ferroelectric domain wall analysis. Using the example of poled lithium niobate, we compare the spectral output of both techniques in terms of domain wall signatures and imaging capabilities. We extract the Raman-like resonant part of the coherent anti-Stokes signal via a Kramers–Kronig-based phase retrieval algorithm and compare the raw and phase-retrieved signals to SR characteristics. Finally, we propose a mechanism for the observed domain wall signal strength that resembles a Čerenkov-like behavior, in close analogy to domain wall signatures obtained by second-harmonic generation imaging. We, thus, lay here the foundations for future investigations on other poled ferroelectric crystals using B-CARS.}}, author = {{Reitzig, Sven and Hempel, Franz and Ratzenberger, Julius and Hegarty, Peter A. and Amber, Zeeshan H. and Buschbeck, Robin and Rüsing, Michael and Eng, Lukas M.}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, keywords = {{Physics and Astronomy (miscellaneous)}}, number = {{16}}, publisher = {{AIP Publishing}}, title = {{{High-speed hyperspectral imaging of ferroelectric domain walls using broadband coherent anti-Stokes Raman scattering}}}, doi = {{10.1063/5.0086029}}, volume = {{120}}, year = {{2022}}, } @article{47989, abstract = {{Thin-film materials from μm thickness down to single-atomic-layered 2D materials play a central role in many novel electronic and optical applications. Coherent, nonlinear optical (NLO) μ-spectroscopy offers insight into the local thickness, stacking order, symmetry, or electronic and vibrational properties. Thin films and 2D materials are usually supported on multi-layered substrates leading to (multi-)reflections, interference, or phase jumps at interfaces during μ-spectroscopy, which all can make the interpretation of experiments particularly challenging. The disentanglement of the influence parameters can be achieved via rigorous theoretical analysis. In this work, we compare two self-developed modeling approaches, a semi-analytical and a fully vectorial model, to experiments carried out in thin-film geometry for two archetypal NLO processes, second-harmonic and third-harmonic generation. In particular, we demonstrate that thin-film interference and phase matching do heavily influence the signal strength. Furthermore, we work out key differences between three and four photon processes, such as the role of the Gouy-phase shift and the focal position. Last, we can show that a relatively simple semi-analytical model, despite its limitations, is able to accurately describe experiments at a significantly lower computational cost as compared to a full vectorial modeling. This study lays the groundwork for performing quantitative NLO μ-spectroscopy on thin films and 2D materials, as it identifies and quantifies the impact of the corresponding sample and setup parameters on the NLO signal, in order to distinguish them from genuine material properties.<}}, author = {{Amber, Zeeshan H. and Spychala, Kai J. and Eng, Lukas M. and Rüsing, Michael}}, issn = {{0021-8979}}, journal = {{Journal of Applied Physics}}, keywords = {{General Physics and Astronomy}}, number = {{21}}, publisher = {{AIP Publishing}}, title = {{{Nonlinear optical interactions in focused beams and nanosized structures}}}, doi = {{10.1063/5.0125926}}, volume = {{132}}, year = {{2022}}, } @article{47988, abstract = {{Second harmonic (SH) microscopy represents a powerful tool for the investigation of crystalline systems, such as ferroelectrics and their domain walls (DWs). Under the condition of normal dispersion, i.e., the refractive index at the SH wavelength is larger as compared to the refractive index at the fundamental wavelength, n(2ω)>n(ω), bulk crystals will generate no SH signal. Should the bulk, however, contain DWs, an appreciable SH signal will still be detectable at the location of DWs stemming from the Čerenkov mechanism. In this work, we demonstrate both how SH signals are generated in bulk media and how the Čerenkov mechanism can be inhibited by using anomalous dispersion, i.e., n(ω)A new decomposition mechanism for trimethylborane at high temperatures has been discovered.}}, author = {{Schleier, Domenik and Gerlach, Marius and Schaffner, Dorothee and Mukhopadhyay, Deb Pratim and Hemberger, Patrick and Fischer, Ingo}}, issn = {{1463-9076}}, journal = {{Physical Chemistry Chemical Physics}}, keywords = {{Physical and Theoretical Chemistry, General Physics and Astronomy}}, number = {{6}}, pages = {{4511--4518}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{Threshold photoelectron spectroscopy of trimethylborane and its pyrolysis products}}}, doi = {{10.1039/d2cp04513c}}, volume = {{25}}, year = {{2022}}, } @article{35322, author = {{Bux, Kai-Uwe and Hilgert, Joachim and Weich, Tobias}}, issn = {{1664-039X}}, journal = {{Journal of Spectral Theory}}, keywords = {{Geometry and Topology, Mathematical Physics, Statistical and Nonlinear Physics}}, number = {{2}}, pages = {{659--681}}, publisher = {{European Mathematical Society - EMS - Publishing House GmbH}}, title = {{{Poisson transforms for trees of bounded degree}}}, doi = {{10.4171/jst/414}}, volume = {{12}}, year = {{2022}}, } @article{36332, abstract = {{AlSi casting alloys combine excellent castability with high strength. Hence, this group of alloys is often used in the automotive sector. The challenge for this application is the brittle character of these alloys which leads to cracks during joint formation when mechanical joining technologies are used. A rise in ductility can be achieved by a considerable increase in the solidification rate which results in grain refinement. High solidification rates can be realized in twin–roll casting (TRC) by water-cooled rolls. Therefore, a hypoeutectic EN AC–AlSi9 (for European Norm - aluminum cast product) is manufactured by the TRC process and analyzed. Subsequently, joining investigations are performed on castings in as-cast and heat-treated condition using the self-piercing riveting process considering the joint formation and the load-bearing capacity. Due to the fine microstructure, the crack initiation can be avoided during joining, while maintaining the joining parameters, especially by specimens in heat treatment conditions. Furthermore, due to the extremely fine microstructure, the load-bearing capacity of the joint can be significantly increased in terms of the maximum load-bearing force and the energy absorbed.}}, author = {{Neuser, Moritz and Kappe, Fabian and Ostermeier, Jakob and Krüger, Jan Tobias and Bobbert, Mathias and Meschut, Gerson and Schaper, Mirko and Grydin, Olexandr}}, issn = {{1438-1656}}, journal = {{Advanced Engineering Materials}}, keywords = {{Condensed Matter Physics, General Materials Science}}, number = {{10}}, publisher = {{Wiley}}, title = {{{Mechanical Properties and Joinability of AlSi9 Alloy Manufactured by Twin‐Roll Casting}}}, doi = {{10.1002/adem.202200874}}, volume = {{24}}, year = {{2022}}, } @article{53080, abstract = {{Quantitative speciation data for alternative fuels is highly desired to assess their emission potential and to develop and validate chemical kinetic models. In terms of substitute choices for fossil diesel are oxymethylene ethers (OMEs) strongly discussed. Due to the absence of carbon-carbon bonds, soot emis-sions from combustion of OMEs are low, but significant emissions of unregulated pollutants such as alde-hydes emerge. The combustion behavior of OME fuels with different chain lengths, OME0-4, was investigated in lam-inar premixed low-pressure flames using complementary molecular-beam mass spectrometry (MBMS) techniques. MBMS sampling provides an in-situ access directly into the reaction zone of the flame. Al-most all chemical species involved in the oxidation process can be detected and quantified simultane-ously. Neat OME0-3 flames were analyzed by electron ionization (EI) MBMS with high mass resolution ( R approximate to 3900) providing exact elementary composition. To obtain isomer-specific information, an OME1- doped hydrogen flame and a stochiometric OME4 flame were studied by double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy. Both, EI-MBMS detection and i2PEPICO spectroscopy, en-ables a complete overview of all intermediates. The results show a dominance of oxygenated intermediates for all measured conditions. Mole fraction profiles for the most important species are presented (i.e. formaldehyde, methanol, methyl formate and formic acid) and compared to modeling results. Hydrocarbons with more than four carbon atoms were not detected under the investigated conditions. Isomers such as ethanol/dimethyl ether (m/z = 46) and ethenol/acetaldehyde (m/z = 44) could be separated using threshold photoelectron spectra for clear iden-tification and photoionization efficiency curves for quantification. This investigation permits the discus-sion and analysis of systematic trends, including intermediate species, for the combustion of the studied series of oxymethylene ether fuels. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.}}, author = {{Gaiser, Nina and Zhang, Hao and Bierkandt, Thomas and Schmitt, Steffen and Zinsmeister, Julia and Kathrotia, Trupti and Hemberger, Patrick and Shaqiri, Shkelqim and Kasper, Tina and Aigner, Manfred and Oßwald, Patrick and Köhler, Markus}}, issn = {{0010-2180}}, journal = {{Combustion and Flame}}, keywords = {{General Physics and Astronomy, Energy Engineering and Power Technology, Fuel Technology, General Chemical Engineering, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{Investigation of the combustion chemistry in laminar, low-pressure oxymethylene ether flames (OME0–4)}}}, doi = {{10.1016/j.combustflame.2022.112060}}, volume = {{243}}, year = {{2022}}, } @article{53081, abstract = {{Recent progress in molecular combustion chemistry allows for detailed investigation of the intermediate species pool even for complex chemical fuel compositions, as occur for technical fuels. This study pro-vides detailed investigation of a comprehensive set of complex alternative gasoline fuels obtained from laminar flow reactors equipped with molecular-beam sampling techniques for observation of the com-bustion intermediate species pool in homogeneous gas phase reactions. The combination of ionization techniques including double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy enables deeper mechanistic insights into the underlying reaction network relevant to technical fuels. The se-lected fuels focus on contemporary automotive engine application as drop-in fuels compliant to European EN 228 specification for gasoline. Therefore, potential alternative gasoline blends containing oxygenated hydrocarbons as octane improvers obtainable from bio-technological production routes, e.g., ethanol, iso- butanol, methyl tert -butyl ether (MTBE), and ethyl tert -butyl ether (ETBE), as well as a Fischer-Tropsch surrogate were investigated. The fuel set is completed by two synthetic naphtha fractions obtained from Fischer-Tropsch and methanol-to-gasoline processes alongside with a fossil reference gasoline. In total, speciation data for 11 technical fuels from two atmospheric flow reactor setups are presented. Detailed main and intermediate species profiles are provided for slightly rich ( 4) = 1.2) and lean ( 4) = 0.8) con-ditions for intermediate to high temperatures. Complementary, the isomer distribution on different mass channels, like m/z = 78 u fulvene/benzene, of four gasolines was investigated. Experimental findings are analyzed in terms of the detailed fuel composition and literature findings for molecular combustion chemistry. Influences of oxygenated fuel components as well as composition of the hydrocarbon frac-tions are examined with a particular focus on the soot precursor chemistry. This dataset is available for validation of chemical kinetic mechanisms for realistic gasolines containing oxygenated hydrocarbons.(c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.}}, author = {{Zinsmeister, Julia and Gaiser, Nina and Melder, Jens and Bierkandt, Thomas and Hemberger, Patrick and Kasper, Tina and Aigner, Manfred and Köhler, Markus and Oßwald, Patrick}}, issn = {{0010-2180}}, journal = {{Combustion and Flame}}, keywords = {{General Physics and Astronomy, Energy Engineering and Power Technology, Fuel Technology, General Chemical Engineering, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{On the diversity of fossil and alternative gasoline combustion chemistry: A comparative flow reactor study}}}, doi = {{10.1016/j.combustflame.2021.111961}}, volume = {{243}}, year = {{2022}}, } @article{53084, abstract = {{AbstractThe thermal decomposition of Zr(acac)4 is studied in a SiC-microreactor on the micro-second time scale. By utilizing synchrotron radiation and photoelectron photoion coincidence spectroscopy, six important zirconium intermediates, as for instance Zr(C5H7O2)2(C5H6O2), and Zr(C5H6O2)2, are identified in the gas phase for the first time. The adiabatic ionization thresholds of intermediately formed zirconium species are estimated and the main products of their thermal decomposition, acetylacetone, acetylallene and acetone are characterized unambiguously and isomer-selectively. Based on all detected intermediates, we deduce the predominant pyrolysis pathways of the precursor in the temperature range from 400 to 900 K. Our findings are complemented by numerical simulations of the flow field in the microreactor, which show that the choice of dilution gas significantly influences the temperature profile and residence times in the microreactor, such that helium provides a more uniform flow field than argon and should preferentially be used. Graphical abstract Using a soft ionization method coupled to velocity map imaging (VMI), leads to valuable insights in the thermal decomposition of Zr(C5H7O2)4, used in the synthesis of functional nanomaterials and ceramic coatings. Thanks to the use of a microreactor, important gas}}, author = {{Grimm, Sebastian and Baik, Seung-Jin and Hemberger, Patrick and Kasper, Tina and Kempf, Andreas M. and Atakan, Burak}}, issn = {{0884-2914}}, journal = {{Journal of Materials Research}}, keywords = {{Mechanical Engineering, Mechanics of Materials, Condensed Matter Physics, General Materials Science}}, number = {{9}}, pages = {{1558--1575}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Insights into the decomposition of zirconium acetylacetonate using synchrotron radiation: Routes to the formation of volatile Zr-intermediates}}}, doi = {{10.1557/s43578-022-00566-6}}, volume = {{37}}, year = {{2022}}, } @article{47552, author = {{Herrmann, Felix and Grünewald, Marcus and Riese, Julia}}, issn = {{0360-3199}}, journal = {{International Journal of Hydrogen Energy}}, keywords = {{Energy Engineering and Power Technology, Condensed Matter Physics, Fuel Technology, Renewable Energy, Sustainability and the Environment}}, number = {{25}}, pages = {{9377--9389}}, publisher = {{Elsevier BV}}, title = {{{Model-based design of a segmented reactor for the flexible operation of the methanation of CO2}}}, doi = {{10.1016/j.ijhydene.2022.12.122}}, volume = {{48}}, year = {{2022}}, } @article{36874, author = {{Su, Jiangling and González Orive, Alejandro and Grundmeier, Guido}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, keywords = {{Surfaces, Coatings and Films, Condensed Matter Physics, Surfaces and Interfaces, General Physics and Astronomy, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{Nano-FTIR and chemical force analysis of electrografted aryldiazonium salts on ODT-microcontact printed Au-surfaces}}}, doi = {{10.1016/j.apsusc.2022.155355}}, volume = {{609}}, year = {{2022}}, } @article{36872, author = {{Bobzin, K. and Kalscheuer, C. and Grundmeier, Guido and de los Arcos, T. and Kollmann, S. and Carlet, M.}}, issn = {{0257-8972}}, journal = {{Surface and Coatings Technology}}, keywords = {{Materials Chemistry, Surfaces, Coatings and Films, Surfaces and Interfaces, Condensed Matter Physics, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{Oxidation stability of chromium aluminum oxynitride hard coatings}}}, doi = {{10.1016/j.surfcoat.2022.128927}}, volume = {{449}}, year = {{2022}}, } @article{36817, author = {{Hoener, Martin and Kasper, Tina}}, issn = {{0010-2180}}, journal = {{Combustion and Flame}}, keywords = {{General Physics and Astronomy, Energy Engineering and Power Technology, Fuel Technology, General Chemical Engineering, General Chemistry}}, publisher = {{Elsevier BV}}, title = {{{Nitrous acid in high-pressure oxidation of CH4 doped with nitric oxide: Challenges in the isomer-selective detection and quantification of an elusive intermediate}}}, doi = {{10.1016/j.combustflame.2022.112096}}, volume = {{243}}, year = {{2022}}, }