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Author: Mändl, Stephan × DDC: 540 ×

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    Carbon and Neon Ion Bombardment Induced Smoothing and Surface Relaxation of Titania Nanotubes
    (Basel : MDPI, 2021) Kupferer, Astrid; Mensing, Michael; Lehnert, Jan; Mändl, Stephan; Mayr, Stefan G.
    Titania nanotube arrays with their enormous surface area are the subject of much attention in diverse fields of research. In the present work, we show that not only 60 keV and 150 keV ion bombardment of amorphous titania nanotube arrays yields defect creation within the tube walls, but it also changes the surface morphology: the surface relaxes and smoothens in accordance with a curvature-driven surface material’s transport mechanism, which is mediated by radiation-induced viscous flow or radiation-enhanced surface diffusion, while the nanotubes act as additional sinks for the particle surface currents. These effects occur independently of the ion species: both carbon and neon ion bombardments result in comparable surface relaxation responses initiated by an ion energy of 60 keV at a fluence of 1 × 1016 ions/cm2. Using atomic force microscopy and contact angle measurements, we thoroughly study the relaxation effects on the surface topography and surface free energy, respectively. Moreover, surface relaxation is accompanied by further amorphization in surface-near regions and a reduction in the mass density, as demonstrated by Raman spectroscopy and X-ray reflectivity. Since ion bombardment can be performed on global and local scales, it constitutes a versatile tool to achieve well-defined and tunable topographies and distinct surface characteristics. Hence, different types of nanotube arrays can be modified for various applications.
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    Compositional Patterning in Carbon Implanted Titania Nanotubes
    (Weinheim : Wiley-VCH, 2021) Kupferer, Astrid; Holm, Alexander; Lotnyk, Andriy; Mändl, Stephan; Mayr, Stefan G.
    Ranging from novel solar cells to smart biosensors, titania nanotube arrays constitute a highly functional material for various applications. A promising route to modify material characteristics while preserving the amorphous nanotube structure is present when applying low-energy ion implantation. In this study, the interplay of phenomenological effects observed upon implantation of low fluences in the unique 3D structure is reported: sputtering versus readsorption and plastic flow, amorphization versus crystallization and compositional patterning. Patterning within the oxygen and carbon subsystem is revealed using transmission electron microscopy. By applying a Cahn–Hilliard approach within the framework of driven alloys, characteristic length scales are derived and it is demonstrated that compositional patterning is expected on free enthalpy grounds, as predicted by density functional theory based ab initio calculations. Hence, an attractive material with increased conductivity for advanced devices is provided. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
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    Oberflächenchemie nano- und mikrodimensionaler Materialien und Werkstoffe : Schlussbericht zum Vorhaben ; Laufzeit: 01.09.2008 bis 31.01.2012
    (Hannover : Technische Informationsbibliothek (TIB), 2012) Rauschenbach, Bernd; Gerlach, Jürgen W.; Hirsch, Dietmar; Mändl, Stephan; Arnold, Th.; Mießler, André; Prager, Lutz; Prager, Andrea; Elsner, Christian; Reichelt, Senta; Pender, Alya
    [no abstract available]