TY - CHAP A1 - Schreiner, Rupert A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Mingels, Stephan A1 - Serbun, Pavel A1 - Müller, Günter T1 - Field emission from surface textured extraction facets of GaN light emitting diodes T2 - 26th International Vacuum Nanoelectronics Conference (IVNC), 8-12 July 2013, Roanoke, VA, USA N2 - We report on the field emission properties of GaN LED surfaces. The textured extraction facet acts both as light scattering layer in order to increase the light extraction efficiency of the LED as well as nanostructured cathode surface for the field emission (FE) of electrons. The LED emits blue light with a peak wavelength of around 450 nm. The FE properties were investigated by a scanning microscope. Integral measurements as well as regulated voltage scans for 1 nA FE current over an area of 400 * 400 µm2were used to investigate both overall and local FE properties. A high number of well-distributed emitters with an average field enhancement factor ß of 85 and stable integral emission currents up to 100 µA at an electric field of   80 V/µm (Øanode= 880 µm) were found. Photo-field-emission spectroscopy (PFES) using a tunable pulsed laser revealed an enhanced photo absorption of the InGaN/GaN quantum well structures near the emission wavelength of the LED (<3.5 eV), whereas at high photon energies (>4.1 eV) photoemission from the GaN surface was observed. KW - Gallium nitride KW - Iron KW - Light emitting diodes KW - Cathodes KW - Surface texture KW - Surface waves KW - Photonics Y1 - 2013 U6 - https://doi.org/10.1109/ivnc.2013.6624721 PB - IEEE ER - TY - CHAP A1 - Moser, Elisabeth A1 - Pangerl, Jonas A1 - Jobst, Simon A1 - Weigl, Stefan A1 - Bierl, Rudolf T1 - Modeling the Photoacoustic Spectrum of a Quantum Cascade Laser for Human Breath T2 - Optical Sensors and Sensing Congress 2022 (AIS, LACSEA, Sensors, ES): July 11 - 15, 2022, Vancouver, British Columbia Canada N2 - A modeling approach to create a photoacoustic spectrum from synthetic data is presented and evaluated. The resulting model reaches a MAPE score of 2.7% and can be used to enable data-driven development in future work. KW - Quantenkaskadenlaser KW - Photoakustische Spektrometrie KW - Atemluft Y1 - 2022 SN - 978-1-957171-10-4 U6 - https://doi.org/10.1364/AIS.2022.ATu3G.2 PB - Optica Publishing Group ER - TY - JOUR A1 - Goldschmidt, Jens A1 - Moser, Elisabeth A1 - Nitzsche, Leonard A1 - Bierl, Rudolf A1 - Wöllenstein, Jürgen T1 - Improving the performance of artificial neural networks trained on synthetic data in gas spectroscopy – a study on two sensing approaches JF - tm - Technisches Messen N2 - Artificial neural networks (ANNs) are used in quantitative infrared gas spectroscopy to predict concentrations on multi-component absorption spectra. Training of ANNs requires vast amounts of labelled training data which may be elaborate and time consuming to obtain. Additional data can be gained by the utilization of synthetically generated spectra, but at the cost of systematic deviations to measured data. Here, we present two approaches to train ANNs with a combination of comparatively small, measured data sets and synthetically generated data. For the first approach a neural network is trained hybridly with synthetically generated infrared absorption spectra of mixtures of N2O and CO and measured zero-gas spectra, taken with a mid-infrared dual comb spectrometer. This improves the mean absolute error (MAE) of the network predictions from 0.46 to 0.01 ppmV and 0.24 to 0.01 ppmV for the concentration predictions of N2O and CO respectively for zero-gas measurements which was previously observed for training with purely synthetic data. At the same time a similar performance on spectra from gas mixtures of 0–100 ppmV N2O and 0 to 60 ppmV CO was achieved. For the second approach an ANN pre-trained on synthetic infrared spectra of mixtures of acetone and ethanol is retrained on a small dataset consisting of 26 spectra taken with a mid-infrared photoacoustic spectrometer. In this case the MAE for the concentration predictions of ethanol and acetone are improved by 45 % and 20 % in comparison to purely synthetic training. This shows the capability of using synthetically generated data to train ANNs in combination with small amounts of measured data to further improve neural networks for gas sensing and the transferability between different sensing approaches. N2 - Künstliche neuronale Netze werden in der quantitativen Infrarot-Gasspektroskopie eingesetzt, um Gaskonzentrationen in Multi-Komponenten-Absorptionsspektren vorherzusagen. Das Training von künstlichen neuronalen Netzen benötigt große Mengen an Trainingsdaten, was mit einem hohen Arbeits- und Zeitaufwand verbunden ist. Zusätzliche Trainingsdaten können durch synthetisch generierte Spektren gewonnen werden, sind jedoch mit systematischen Abweichungen zu tatsächlich gemessenen Daten verbunden. In dieser Arbeit werden zwei Ansätze präsentiert, um künstliche neuronale Netze mit einer Kombination aus vergleichsweise kleinen, gemessenen Datensätzen und synthetisch erzeugten Daten zu trainieren. Für den ersten Ansatz wird das neuronale Netz hybrid mit synthetisch erzeugten Infrarot-Absorptionsspektren von Mischungen aus N2O und CO und gemessenen Null-Gas-Spektren trainiert, welche mit einem Doppel-Kamm-Spektrometer im Mittelinfraroten aufgenommen wurden. Dieses Vorgehen verbessert den mittleren, absoluten Fehler der Netzvorhersagen von 0,46 auf 0,01 ppmV und 0,24 auf 0,01 ppmV für N2O bzw. für CO für Null-Gas-Messungen, im Vergleich zu den Vorhersagen des neuronalen Netzes, welches nur mit synthetisch erzeugten Daten trainiert wurde. Gleichzeitig zeigte das hybrid trainierte Netz eine gleichbleibende Performance für Konzentrationsvorhersagen für Spektren aus Gasmischungen von 0 bis 100 ppmV N2O und 0 bis 60 ppmV CO. Für den zweiten Ansatz wird ein neuronales Netz, welches bereits mit synthetischen erzeugten Infrarotspektren von Mischungen aus Aceton und Ethanol trainiert wurde, erneut auf einem kleinen gemessenen Datensatz bestehend aus 26 Spektren trainiert, welche mit einem photoakustischen Spektrometer im mittleren Infrarot aufgenommen wurden. In diesem Fall hat sich der mittlere absolute Fehler der Konzentrationsvorhersage für Ethanol und Aceton um 45 % bzw. 20 % im Vergleich zu einem rein synthetischen Training verbessert. Das zeigt das Potential synthetisch erzeugte Daten für das Training von künstlichen neuronalen Netzen in Kombination mit kleinen gemessenen Datensätzen zu nutzen, um neuronale Netze für den Einsatz im Bereich der Gassensorik zu verbessern und gleichzeitig die Übertragbarkeit der Methodik auf verschiedene Messansätze. Y1 - 2023 U6 - https://doi.org/10.1515/teme-2023-0051 PB - Oldenbourg Wissenschaftsverlag ET - Online veröffentlicht ER - TY - CHAP A1 - Ulreich, Fabian A1 - Moser, Elisabeth A1 - Olbrich, Florian A1 - Ebert, Martin A1 - Bierl, Rudolf A1 - Kaup, André ED - Keil, Rudolf ED - Tschorn, Jan Alexander ED - Tümler, Johannes ED - Altinsoy, Mehmet Ercan T1 - Luminance Simulation in CARLA under Cloud Coverage - Model Validation and Implications T2 - 2023 IEEE International Workshop on Metrology for Automotive (MetroAutomotive), -30 June 2023, Modena, Italy N2 - To decrease the number of kilometers driven during the development of autonomous cars or driving assistance systems, performant simulation tools are necessary. Currently, domain distance effects between simulation and reality are limiting the successful application of rendering engines in data-driven perception tasks. In order to mitigate those domain distance effects, simulation tools have to be as close to reality as possible for the given task. For optical sensors like cameras, the luminance of the scene is essential. We provide within this paper a method to measure the luminance of rendered scenes within CARLA, an often used open-source simulation environment. Thereby, it is possible to validate the environment and weather models by taking real-world measurements with photometric sensors or with the help of open-source weather data, published e.g. by the German federal service for weather data (DWD - "Deutscher Wetterdienst"). Employing our proposed luminance measurement, the domain gap resulting from the simulation can be specified, which makes it possible to evaluate the statements about the safety of the automated driving system determined within the simulation. We show that the ratio between global and diffuse radiation modeled by the default atmosphere models within CARLA are under limited conditions similar to real-world measurements taken by the DWD. Nevertheless, we show, that the ratio’s temporal variability in real-world situations is not modeled by CARLA. KW - Atmospheric measurements KW - Atmospheric modeling KW - Cameras KW - carla KW - Cloud computing KW - cloud coverage KW - Data models KW - luminance KW - meteorology KW - Simulation KW - Soft sensors KW - weather KW - Wind Y1 - 2023 SN - 979-8-3503-2187-6 U6 - https://doi.org/10.1109/MetroAutomotive57488.2023.10219098 SP - 228 EP - 233 PB - IEEE ER - TY - JOUR A1 - Müller, Max A1 - Weigl, Stefan A1 - Müller-Williams, Jennifer A1 - Lindauer, Matthias A1 - Rück, Thomas A1 - Jobst, Simon A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - Comparison of photoacoustic spectroscopy and cavity ring-down spectroscopy for ambient methane monitoring at Hohenpeißenberg JF - Atmospheric Measurement Techniques N2 - With an atmospheric concentration of approximately 2000 parts per billion (ppbV, 10−9), methane (CH4) is the second most abundant greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO2). The task of long-term and spatially resolved GHG monitoring to verify whether climate policy actions are effective is becoming more crucial as climate change progresses. In this paper we report the CH4 concentration readings of our photoacoustic (PA) sensor over a 5 d period at Hohenpeißenberg, Germany. As a reference device, a calibrated cavity ring-down spectrometer, Picarro G2301, from the meteorological observatory of the German Weather Service (DWD) was employed. Trace gas measurements with photoacoustic instruments promise to provide low detection limits at comparably low costs. However, PA devices are often susceptible to cross-sensitivities related to fluctuating environmental conditions, e.g. ambient humidity. The obtained results show that for PA sensor systems non-radiative relaxation effects induced by varying humidity are a non-negligible factor. Applying algorithm compensation techniques, which are capable of calculating the influence of non-radiative relaxation effects on the photoacoustic signal, increase the accuracy of the photoacoustic sensor significantly. With an average relative deviation of 1.11 % from the G2301, the photoacoustic sensor shows good agreement with the reference instrument. Y1 - 2023 U6 - https://doi.org/10.5194/amt-16-4263-2023 SN - 1867-8548 VL - 16 IS - 18 SP - 4263 EP - 4270 PB - Copernicus Publications ER - TY - JOUR A1 - Fritz, D. M. A1 - Reis, D. A. A1 - Adams, B. A1 - Akre, R. A. A1 - Arthur, J. A1 - Blome, Christian A1 - Bucksbaum, P. H. A1 - Cavalieri, A. L. A1 - Engemann, S. A1 - Fahy, S. A1 - Falcone, R. W. A1 - Fuoss, P. H. A1 - Gaffney, K. J. A1 - George, M. J. A1 - Hajdu, J. A1 - Hertlein, M. P. A1 - Hillyard, P. B. A1 - Horn-von Hoegen, Michael A1 - Kammler, Martin A1 - Kaspar, J. A1 - Kienberger, R. A1 - Krejcik, P. A1 - Lee, S. H. A1 - Lindenberg, A. M. A1 - McFarland, B. A1 - Meyer, D. A1 - Montagne, T. A1 - Murray, E. D. A1 - Nelson, A. J. A1 - Nicoul, Matthieu A1 - Pahl, R. A1 - Rudati, J. A1 - Schlarb, H. A1 - Siddons, D. P. A1 - Sokolowski-Tinten, Klaus A1 - Tschentscher, Th A1 - von der Linde, D. A1 - Hastings, J. B. T1 - Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays JF - Science N2 - Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid. Y1 - 2007 U6 - https://doi.org/10.1126/science.1135009 VL - 315 IS - 5812 SP - 633 EP - 636 PB - AAAS ER - TY - CHAP A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Blums, Juris A1 - Shymanovich, Uladzimir A1 - Nicoul, Matthieu A1 - Cavalleri, Andrea A1 - Tarasevitch, A. A1 - Horn-von Hoegen, Michael A1 - Kammler, Martin A1 - von der Linde, Dietrich ED - Kobayashi, Tetsuro T1 - Ultrafast X-ray diffraction T2 - Ultrafast Phenomena XIV N2 - In the last few years the generation of femtosecond pulses in the X-ray regime has become possible. These ultrashort X-ray pulses have enabled femtosecond time- resolution to be extended to X-rays. Y1 - 2004 SN - 978-3-540-27213-7 U6 - https://doi.org/10.1007/3-540-27213-5_53 VL - 79 SP - 170 EP - 174 PB - Springer CY - Berlin, Heidelberg ER - TY - JOUR A1 - Kammler, Martin A1 - Horn- von Hoegen, Michael A1 - Voss, N. A1 - Tringides, Michael C. A1 - Menzel, Andreas A1 - Conrad, E. H. T1 - Si(001) step dynamics: A temporal low-energy electron diffraction study JF - Physical Review B N2 - We present equilibrium measurements of the dynamics of steps on Si(001) using temporal electron-diffraction spectroscopy. Activation energies and the rate limiting kinetics are identified for 950K<~T<~1130K. Unlike previous studies at higher temperatures, we can exclude evaporation and condensation of atoms or dimers from the step edges as the rate limiting process in this temperature regime. The possible reason for this difference is discussed in terms of a crossover from different rate-limiting kinetics. Y1 - 2002 U6 - https://doi.org/10.1103/PhysRevB.65.075312 VL - 65 IS - 7 PB - APS ER - TY - CHAP A1 - Navitski, Aliaksandr A1 - Serbun, Pavel A1 - Müller, Günter A1 - Schreiner, Rupert A1 - Dams, Florian T1 - Efficient and reliable field emission from silicon tip arrays for miniaturized electron sources T2 - 2011 24th International Vacuum Nanoelectronics Conference ; 18-22 July 2011 Wuppertal N2 - Silicon-based cathodes with precisely aligned field emitter arrays (FEA) applicable for miniaturized electron sources were successfully developed and fabricated. The cathode chips contain about 3×105 Si tips/cm2 in a triangular array with a tip height of 2.5 μm, tip radius of 20 nm, and lateral distance between tips of 20 μm. Amazingly homogeneous and well-aligned field emission (FE) from all tips (i.e. 100% efficiency) and maximum stable currents of typically 0.1 μA for p- and 0.6 μA for n-type Si were reproducibly achieved. Current-voltage characteristics of p-type Si tips exhibit the expected saturation at around 10 nA due to limited supply of electrons from a depletion layer, while the n-type Si tips show the usual FN behaviour. Additional coating of the Si tips with a 10 nm Au layer resulted in at least 5 times higher average FE current levels i.e. typically 3 μA but lead, however, to a 30% increase of the onset voltage. KW - cathodes KW - coatings KW - elemental semiconductors KW - field emission KW - field emitter arrays KW - miniaturized electron sources KW - silicon tips KW - structured cold cathode Y1 - 2011 UR - https://ieeexplore.ieee.org/document/6004567?arnumber=6004567 SN - 978-3-00-035081-8 SN - 978-1-4577-1243-2 SN - 2380-6311 SN - 2164-2370 SP - 71 EP - 72 PB - IEEE CY - Piscataway, NJ ER - TY - JOUR A1 - Pirker, Luka A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Remškar, Maja A1 - Višić, Bojana T1 - MoₓWₓ₋₁S₂ Nanotubes for Advanced Field Emission Application JF - Advanced Functional Materials N2 - Transition metal dichalcogenide (TMDC) nanotubes complement the field of low-dimensional materials with their quasi-1D morphology and a wide set of intriguing properties. By introducing different transition metals into the crystal structure, their properties can be tailored for specific purpose and applications. Herein, the characterization and a subsequent preparation of single-nanotube field emission devices of MoxWx-1S2 nanotubes prepared via the chemical vapor transport reaction is presented. Energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction indicate that the molybdenum and tungsten atoms are randomly distributed within the crystal structure and that the material is highly crystalline. High resolution transmission electron microscopy and electron diffraction (ED) patterns further corroborate these findings. A detailed analysis of the ED patterns from an eight-layer nanotube reveal that the nanotubes grow in the 2H structure, with each shell consists of one bilayer. The work function of the nanotubes is comparable to that of pure MoS2 and lower of pure WS2 NTs, making them ideal candidates for field emission applications. Two devices with different geometrical setup are prepared and tested as field emitters, showing promising results for single nanotube field emission applications. Y1 - 2023 U6 - https://doi.org/10.1002/adfm.202213869 SN - 1616-3028 N1 - Early View. Online Version of Record before inclusion in an issue SP - 1 EP - 8 PB - Wiley ER - TY - INPR A1 - Pangerl, Jonas A1 - Moser, Elisabeth A1 - Müller, Max A1 - Weigl, Stefan A1 - Jobst, Simon A1 - Rück, Thomas A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - A Highly Sensitive Acetone and Ethanol Quantum Cascade Laser Based Photoacoustic Sensor: Characterization and Multi-Component Spectra Recording in Synthetic Breath T2 - SSRN Electronic Journal N2 - Trace gas analysis in breath is challenging due to the vast number of different components. We present a highly sensitive quantum cascade laser based photoacoustic setup for breath analysis. Scanning the range between 8260 and 8270 nm with a spectral resolution of 48 pm, we are able to quantify acetone and ethanol within a typical breath matrix containing water and CO2. We photoacoustically acquired spectra within this region of mid-infra-red light and prove that those spectra do not suffer from non-spectral interferences. The purely additive behavior of a breath sample spectrum was verified by comparing it with the independently acquired single component spectra using Pearson and Spearman correlation coefficients. A previously presented simulation approach is improved and an error attribution study is presented. With a 3σ detection limit of 6.5 ppbV in terms of ethanol and 250 pptV regarding acetone, our system is among the best performing presented so far. KW - Photoacoustic spectroscopy KW - quantum cascade laser KW - spectral simulation KW - breath analysis KW - acetone Y1 - 2022 U6 - https://doi.org/10.2139/ssrn.4305376 PB - Elsevier ER -