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End date: 2024 × Start date: 2020 × End date: 2024 × Start date: 2020 × DDC: 540 × Version: publishedVersion × WGL Institute: FBH ×

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    The 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, Katja
    Focused 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.
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    The Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB-LED Structures
    (Weinheim : Wiley-VCH, 2020) Knauer, Arne; Mogilatenko, Anna; Weinrich, Jonas; Hagedorn, Sylvia; Walde, Sebastian; Kolbe, Tim; Cancellara, Leonardo; Weyers, Markus
    Strain relaxation mechanisms in AlGaN based light emitting diodes emitting in the ultraviolet B spectral range (UVB-LEDs) grown on different AlN/sapphire templates are analyzed by combining in situ reflectivity and curvature data with transmission electron microscopy. In particular, the impact of dislocation density, surface morphology, and lattice constant of the AlN/sapphire templates is studied. For nonannealed AlN/templates with threading dislocation densities (TDDs) of 4 × 109 and 3 × 109 cm−2 and different surface morphologies strain relaxation takes place mostly by conventional ways, such as inclination of threading dislocation lines and formation of horizontal dislocation bands. In contrast, a TDD reduction down to 1 × 109 cm−2 as well as a reduction of the lattice constant of high temperature annealed AlN template leads to drastic changes in the structure of subsequently grown AlGaN layers, e.g., to transformation to helical dislocations and enhanced surface enlargement by formation of macrofacets. For the growth of strongly compressively strained AlGaN layers for UVB-LEDs the relaxation mechanism is strongly influenced by the absolute values of TDD and the lattice constant of the AlN templates and is less influenced by their surface morphology.
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    Shifted 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, Bernd
    To 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.