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- ItemOptimized diamond inverted nanocones for enhanced color center to fiber coupling(Melville, NY : American Inst. of Physics, 2021) Torun, Cem Güney; Schneider, Philipp-Immanuel; Hammerschmidt, Martin; Burger, Sven; Munns, Joseph H. D.; Schröder, TimNanostructures can be used for boosting the light outcoupling of color centers in diamond; however, the fiber coupling performance of these nanostructures is rarely investigated. Here, we use a finite element method for computing the emission from color centers in inverted nanocones and the overlap of this emission with the propagation mode in a single-mode fiber. Using different figures of merit, the inverted nanocone parameters are optimized to obtain maximal fiber coupling efficiency, free-space collection efficiency, or rate enhancement. The optimized inverted nanocone designs show promising results with 66% fiber coupling or 83% free-space coupling efficiency at the tin-vacancy center zero-phonon line wavelength of 619 nm. Moreover, when evaluated for broadband performance, the optimized designs show 55% and 76% for fiber coupling and free-space efficiencies, respectively, for collecting the full tin-vacancy emission spectrum at room temperature. An analysis of fabrication insensitivity indicates that these nanostructures are robust against imperfections. For maximum emission rate into a fiber mode, a design with a Purcell factor of 2.34 is identified. Finally, possible improvements offered by a hybrid inverted nanocone, formed by patterning into two different materials, are investigated and increase the achievable fiber coupling efficiency to 71%. © 2021 Author(s).
- ItemThe patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2021) Deinhart, Victor; Kern, Lisa-Marie; Kirchhof, Jan N.; Juergensen, Sabrina; Sturm, Joris; Krauss, Enno; Feichtner, Thorsten; Kovalchuk, Sviatoslav; Schneider, Michael; Engel, Dieter; Pfau, Bastian; Hecht, Bert; Bolotin, Kirill I.; Reich, Stephanie; Höflich, KatjaFocused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.
- ItemTemperature dependence of the complex permittivity in microwave range of some industrial polymers(New York, NY : American Inst. of Physics, 2022) Porteanu, Horia-Eugen; Kaempf, Rudolf; Flisgen, Thomas; Heinrich, WolfgangThe microwave properties of a number of polymers common in industry are investigated. A cylindrical resonator in the TM012 mode is used. The cavity perturbation method and detailed COMSOL simulations are applied for extracting the complex permittivity as a function of temperature. The results are useful for the design of plastic processing tools by heating with electromagnetic fields. The intrinsic parameters of absorption are derived based on two exponential decays: polarization and Arrhenius dependence of the decay times on temperature.
- ItemShifted excitation Raman difference spectroscopy as enabling technique for the analysis of animal feedstuff(Chichester [u.a.] : Wiley, 2021) Sowoidnich, Kay; Oster, Michael; Wimmers, Klaus; Maiwald, Martin; Sumpf, BerndTo achieve the best performance and health in farm animals, high-quality pellets should be applied for feeding. Raw materials used for pellet production can have a significant influence on the nutritive and physical characteristics of the final product. A comprehensive quality control of raw materials and pellets is therefore essential. Optical inspection techniques show great promise as they enable fast, simple, and non-destructive analysis. This study demonstrates the potential of shifted excitation Raman difference spectroscopy (SERDS) for inspection of intact feed pellets and their constituents. SERDS combines the ability of conventional Raman spectroscopy to obtain chemically specific information from the sample with efficient fluorescence background rejection capabilities. The latter is an essential prerequisite for the application to highly fluorescent natural samples, for example, feedstuffs. A custom dual-wavelength diode laser with two slightly shifted emission wavelengths (785.2 and 784.6 nm) as required for SERDS is used as excitation light source. Results demonstrate that Raman signals can efficiently be separated from unwanted background contributions allowing for qualitative spatially resolved analysis of chicken feed pellets. Individual constituents present at levels down to 10 g/kg were successfully detected by means of their characteristic spectral signature. This highlights the large potential of SERDS and could pave the way for future inspection of raw materials and pellets at selected points along the process chain.
- ItemEuPRAXIA Conceptual Design Report(Berlin ; Heidelberg : Springer, 2020) Assmann, R. W.; Weikum, M. K.; Akhter, T.; Alesini, D.; Alexandrova, A. S.; Anania, M. P.; Andreev, N. E.; Andriyash, I.; Artioli, M.; Aschikhin, A.; Audet, T.; Jafarinia, F. J.; Jakobsson, O.; Jaroszynski, D. A.; Jaster-Merz, S.; Joshi, C.; Kaluza, M.; Kando, M.; Karger, O. S.; Karsch, S.; Khazanov, E.; Bacci, A.; Khikhlukha, D.; Kirchen, M.; Kirwan, G.; Kitégi, C.; Knetsch, A.; Kocon, D.; Koester, P.; Kononenko, O. S.; Korn, G.; Kostyukov, I.; Barna, I. F.; Kruchinin, K. O.; Labate, L.; Le Blanc, C.; Lechner, C.; Lee, P.; Leemans, W.; Lehrach, A.; Li, X.; Li, Y.; Libov, V.; Bartocci, S.; Lifschitz, A.; Lindstrøm, C. A.; Litvinenko, V.; Lu, W.; Lundh, O.; Maier, A. R.; Malka, V.; Manahan, G. G.; Mangles, S. P. D.; Marcelli, A.; Bayramian, A.; Marchetti, B.; Marcouillé, O.; Marocchino, A.; Marteau, F.; Martinez de la Ossa, A.; Martins, J. L.; Mason, P. D.; Massimo, F.; Mathieu, F.; Maynard, G.; Beaton, A.; Mazzotta, Z.; Mironov, S.; Molodozhentsev, A. Y.; Morante, S.; Mosnier, A.; Mostacci, A.; Müller, A. -S.; Murphy, C. D.; Najmudin, Z.; Nghiem, P. A. P.; Beck, A.; Nguyen, F.; Niknejadi, P.; Nutter, A.; Osterhoff, J.; Oumbarek Espinos, D.; Paillard, J. -L.; Papadopoulos, D. N.; Patrizi, B.; Pattathil, R.; Pellegrino, L.; Bellaveglia, M.; Petralia, A.; Petrillo, V.; Piersanti, L.; Pocsai, M. A.; Poder, K.; Pompili, R.; Pribyl, L.; Pugacheva, D.; Reagan, B. A.; Resta-Lopez, J.; Beluze, A.; Ricci, R.; Romeo, S.; Rossetti Conti, M.; Rossi, A. R.; Rossmanith, R.; Rotundo, U.; Roussel, E.; Sabbatini, L.; Santangelo, P.; Sarri, G.; Bernhard, A.; Schaper, L.; Scherkl, P.; Schramm, U.; Schroeder, C. B.; Scifo, J.; Serafini, L.; Sharma, G.; Sheng, Z. M.; Shpakov, V.; Siders, C. W.; Biagioni, A.; Silva, L. O.; Silva, T.; Simon, C.; Simon-Boisson, C.; Sinha, U.; Sistrunk, E.; Specka, A.; Spinka, T. M.; Stecchi, A.; Stella, A.; Bielawski, S.; Stellato, F.; Streeter, M. J. V.; Sutherland, A.; Svystun, E. N.; Symes, D.; Szwaj, C.; Tauscher, G. E.; Terzani, D.; Toci, G.; Tomassini, P.; Bisesto, F. G.; Torres, R.; Ullmann, D.; Vaccarezza, C.; Valléau, M.; Vannini, M.; Vannozzi, A.; Vescovi, S.; Vieira, J. M.; Villa, F.; Wahlström, C. -G.; Bonatto, A.; Walczak, R.; Walker, P. A.; Wang, K.; Welsch, A.; Welsch, C. P.; Weng, S. M.; Wiggins, S. M.; Wolfenden, J.; Xia, G.; Yabashi, M.; Boulton, L.; Zhang, H.; Zhao, Y.; Zhu, J.; Zigler, A.; Brandi, F.; Brinkmann, R.; Briquez, F.; Brottier, F.; Bründermann, E.; Büscher, M.; Buonomo, B.; Bussmann, M. H.; Bussolino, G.; Campana, P.; Cantarella, S.; Cassou, K.; Chancé, A.; Chen, M.; Chiadroni, E.; Cianchi, A.; Cioeta, F.; Clarke, J. A.; Cole, J. M.; Costa, G.; Couprie, M. -E.; Cowley, J.; Croia, M.; Cros, B.; Crump, P. A.; D’Arcy, R.; Dattoli, G.; Del Dotto, A.; Delerue, N.; Del Franco, M.; Delinikolas, P.; De Nicola, S.; Dias, J. M.; Di Giovenale, D.; Diomede, M.; Di Pasquale, E.; Di Pirro, G.; Di Raddo, G.; Dorda, U.; Erlandson, A. C.; Ertel, K.; Esposito, A.; Falcoz, F.; Falone, A.; Fedele, R.; Ferran Pousa, A.; Ferrario, M.; Filippi, F.; Fils, J.; Fiore, G.; Fiorito, R.; Fonseca, R. A.; Franzini, G.; Galimberti, M.; Gallo, A.; Galvin, T. C.; Ghaith, A.; Ghigo, A.; Giove, D.; Giribono, A.; Gizzi, L. A.; Grüner, F. J.; Habib, A. F.; Haefner, C.; Heinemann, T.; Helm, A.; Hidding, B.; Holzer, B. J.; Hooker, S. M.; Hosokai, T.; Hübner, M.; Ibison, M.; Incremona, S.; Irman, A.; Iungo, F.This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.
- ItemModelling of a miniature microwave driven nitrogen plasma jet and comparison to measurements(Bristol : IOP Publ., 2021) Klute, Michael; Kemaneci, Efe; Porteanu, Horia-Eugen; Stefanović, Ilija; Heinrich, Wolfgang; Awakowicz, Peter; Brinkmann, Ralf PeterThe MMWICP (miniature microwave ICP) is a new plasma source using the induction principle. Recently Klute et al presented a mathematical model for the electromagnetic fields and power balance of the new device. In this work the electromagnetic model is coupled with a global chemistry model for nitrogen, based on the chemical reaction set of Thorsteinsson and Gudmundsson and customized for the geometry of the MMWICP. The combined model delivers a quantitative description for a non-thermal plasma at a pressure of p = 1000 Pa and a gas temperature of Tg = 650–1600 K. Comparison with published experimental data shows a good agreement for the volume averaged plasma parameters at high power, for the spatial distribution of the discharge and for the microwave measurements. Furthermore, the balance of capacitive and inductive coupling in the absorbed power is analyzed. This leads to the interpretation of the discharge regime at an electron density of ne ≈ 6.4 × 1018 m−3 as E/H-hybridmode with an capacitive and inductive component.
- ItemHigh‐Temperature Annealing and Patterned AlN/Sapphire Interfaces(Weinheim : Wiley-VCH, 2021) Hagedorn, Sylvia; Mogilatenko, Anna; Walde, Sebastian; Pacak, Daniel; Weinrich, Jonas; Hartmann, Carsten; Weyers, MarkusUsing the example of epitaxial lateral overgrowth of AlN on trench-patterned AlN/sapphire templates, the impact of introducing a high-temperature annealing step into the process chain is investigated. Covering the open surfaces of sapphire trench sidewalls with a thin layer of AlN is found to be necessary to preserve the trench shape during annealing. Both the influence of annealing temperature and annealing duration are investigated. To avoid the deformation of the AlN/sapphire interface during annealing, the annealing duration or annealing temperature must be low enough. Annealing for 1 h at 1730 °C is found to allow for the lowest threading dislocation density of 3.5 × 108 cm−2 in the subsequently grown AlN, while maintaining an uncracked smooth surface over the entire 2 in. wafer. Transmission electron microscopy study confirms the defect reduction by high-temperature annealing and reveals an additional strain relaxation mechanism by accumulation of horizontal dislocation lines at the interface between annealed and nonannealed AlN. By applying a second annealing step, the dislocation density can be further reduced to 2.5 × 108 cm−2.
- ItemCurrent Status of Carbon‐Related Defect Luminescence in GaN(Weinheim : Wiley-VCH, 2021) Zimmermann, Friederike; Beyer, Jan; Röder, Christian; Beyer, Franziska C.; Richter, Eberhard; Irmscher, Klaus; Heitmann, JohannesHighly insulating layers are a prerequisite for gallium nitride (GaN)-based power electronic devices. For this purpose, carbon doping is one of the currently pursued approaches. However, its impact on the optical and electrical properties of GaN has been widely debated in the scientific community. For further improvement of device performance, a better understanding of the role of related defects is essential. To study optically active point defects, photoluminescence is one of the most frequently used experimental characterization techniques. Herein, the main recent advances in the attribution of carbon-related photoluminescence bands are reviewed, which were enabled by the interplay of a refinement of growth and characterization techniques and state-of-the-art first-principles calculations developed during the last decade. The predicted electronic structures of isolated carbon defects and selected carbon-impurity complexes are compared to experimental results. Taking into account both of these, a comprehensive overview on the present state of interpretation of carbon-related broad luminescence bands in bulk GaN is presented.
- ItemTemperature Dependence of Dark Spot Diameters in GaN and AlGaN(Weinheim : Wiley-VCH, 2021) Netzel, Carsten; Knauer, Arne; Brunner, Frank; Mogilatenko, Anna; Weyers, MarkusThreading dislocations in c-plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called “dark spots.” These areas are observable in luminescence measurements with spatial resolution in the submicrometer range. Dark spots reduce the internal quantum efficiency in single layers and light-emitting devices. In cathodoluminescence measurements, the diameter of dark spots (full width at half maximum [FWHM]) is observed to be 200–250 nm for GaN. It decreases by 30–60% for AlxGa1−xN with x ≈ 0.5. Furthermore, the dark spot diameter increases with increasing temperature from 83 to 300 K in AlGaN, whereas it decreases in GaN. Emission energy mappings around dark spots become less smooth and show sharper features on submicrometer scales at low temperature for AlGaN and, on the contrary, at high temperature for GaN. It is concluded that charge carrier localization dominates the temperature dependence of dark spot diameters and of the emission energy distribution around threading dislocations in AlGaN, whereas the temperature-dependent excitation volume in cathodoluminescence and charge carrier diffusion limited by phonon scattering are the dominant effects in GaN. Consequently, with increasing temperature, nonradiative recombination related to threading dislocations extends to wider regions in AlGaN, whereas it becomes spatially limited in GaN.
- ItemWedged Nd:YVO4 crystal for wavelength tuning of monolithic passively Q-switched picosecond microchip lasers(Washington, DC : Soc., 2021) Marianovich, André; Spiekermann, Stefan; Brendel, Moritz; Wessels, Peter; Neumann, Jörg; Weyers, Markus; Kracht, DietmarWe present a monolithic integrated passively Q-switched sub-150 ps microchip laser at 1064 nm with a wedged Nd:YVO4 crystal operating up to a repetition rate of 1 MHz. The wedge enables to change the cavity length by a small amount to fine tune the spectral cavity mode position over the full gain bandwidth of Nd:YVO4 and hence to optimize the output power. This additional degree of freedom may be a suitable approach to increase the wafer scale mass production yield or also to simplify frequency tuning of CW single-frequency microchip lasers.
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