Browsing by Author "Rauschenbach, Bernd"

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    Biaxially Textured Titanium Thin Films by Oblique Angle Deposition: Conditions and Growth Mechanisms
    (Weinheim : Wiley-VCH, 2020) Liedtke-Grüner, Susann; Grüner, Christoph; Lotnyk, Andriy; Gerlach, Juergen W.; Rauschenbach, Bernd
    Growing highly crystalline nanowires over large substrate areas remains an ambiguous task nowadays. Herein, a time-efficient and easy-to-handle bottom-up approach is demonstrated that enables the self-assembled growth of biaxially textured Ti thin films composed of single-crystalline nanowires in a single-deposition step. Ti thin films are deposited under highly oblique incidence angles by electron beam evaporation on amorphous substrates. Substrate temperature, angle of the incoming particle flux, and working pressure are varied to optimize the crystallinity in those films. Height-resolved structure information of individual nanowires is provided by a transmission electron microscopy (TEM) nanobeam, high-resolution TEM, and electron diffraction. Ti nanowires are polycrystalline at 77 K, whereas for ≥300 K, single-crystalline nanowires are tendentially found. The Ti crystals grow along the thermodynamically favored c-direction, but the nanowires’ tilt angle is determined by shadowing. Biaxially textured Ti thin films require a certain temperature range combined with highly oblique deposition angles, which is proved by X-ray in-plane pole figures. A general correlation between average activation energy for surface self-diffusion and melting point of metals is given to estimate the significant influence of surface self-diffusion on the evolution of obliquely deposited metal thin films.
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    BMBF-Verbundprojekt: Si- und SiGe-Dünnfilme für thermoelektrische Anwendungen, Teilvorhaben "Glancing Angle Deposition von Si-Ge-Nanosäulen" : Abschlussbericht ; Bewilligungszeitraum: 01.07.2009 - 30.06.2012
    (Hannover : Technische Informationsbibliothek (TIB), 2013) Rauschenbach, Bernd; Bauer, Jens; Manova, Darina; Grüner, Christoph
    [no abstract available]
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    Comparative study of sculptured metallic thin films deposited by oblique angle deposition at different temperatures
    (Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2018) Liedtke, Susann; Grüner, Christoph; Gerlach, Jürgen W.; Rauschenbach, Bernd
    Metals with a wide range of melting points are deposited by electron beam evaporation under oblique deposition geometry on thermally oxidized Si substrates. During deposition the sample holder is cooled down to 77 K. It is observed that all obliquely deposited metals grow as tilted, high aspect ratio columns and hence with a similar morphology. A comparison of such columns with those deposited at room temperature (300 K) reveals that shadowing dominates the growth process for columns deposited at 77 K, while the impact of surface diffusion is significantly increased at elevated substrate temperatures. Furthermore, it is discussed how the incidence angle of the incoming particle flux and the substrate temperature affect the columnar tilt angles and the porosity of the sculptured thin films. Exemplarily for tilted Al columns deposited at 77 K and at 300 K, in-plane pole figure measurements are carried out. A tendency to form a biaxial texture as well as a change in the crystalline structure depending on the substrate temperature is found for those films.
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    Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation
    (London : Nature Publishing Group, 2016) Sun, Xinxing; Ehrhardt, Martin; Lotnyk, Andriy; Lorenz, Pierre; Thelander, Erik; Gerlach, Jürgen W.; Smausz, Tomi; Decker, Ulrich; Rauschenbach, Bernd
    The amorphous to crystalline phase transformation of Ge2Sb2Te5 (GST) films by UV nanosecond (ns) and femtosecond (fs) single laser pulse irradiation at the same wavelength is compared. Detailed structural information about the phase transformation is collected by x-ray diffraction and high resolution transmission electron microscopy (TEM). The threshold fluences to induce crystallization are determined for both pulse lengths. A large difference between ns and fs pulse irradiation was found regarding the grain size distribution and morphology of the crystallized films. For fs single pulse irradiated GST thin films, columnar grains with a diameter of 20 to 60 nm were obtained as evidenced by cross-sectional TEM analysis. The local atomic arrangement was investigated by highresolution Cs-corrected scanning TEM. Neither tetrahedral nor off-octahedral positions of Ge-atoms could be observed in the largely defect-free grains. A high optical reflectivity contrast (~25%) between amorphous and completely crystallized GST films was achieved by fs laser irradiation induced at fluences between 13 and 16 mJ/cm2 and by ns laser irradiation induced at fluences between 67 and 130 mJ/cm2. Finally, the fluence dependent increase of the reflectivity is discussed in terms of each photon involved into the crystallization process for ns and fs pulses, respectively.
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    Detection of small bunches of ions using image charges
    (London : Nature Publishing Group, 2018) Räcke, Paul; Spemann, Daniel; Gerlach, Jürgen W.; Rauschenbach, Bernd; Meijer, Jan
    A concept for detection of charged particles in a single fly-by, e.g. within an ion optical system for deterministic implantation, is presented. It is based on recording the image charge signal of ions moving through a detector, comprising a set of cylindrical electrodes. This work describes theoretical and practical aspects of image charge detection (ICD) and detector design and its application in the context of real time ion detection. It is shown how false positive detections are excluded reliably, although the signal-to-noise ratio is far too low for time-domain analysis. This is achieved by applying a signal threshold detection scheme in the frequency domain, which - complemented by the development of specialised low-noise preamplifier electronics - will be the key to developing single ion image charge detection for deterministic implantation.
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    ESCA- und SIMS-Untersuchungen an ionenausgetauschten Glasoberflächen
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1982) Hähnert, Manfred; Müller, Wolfgang; Richter, W.; Rauschenbach, Bernd
    Oberflächennahe Konzentrationsprofile werden an einem K/Na-ionenausgetauschten Natrium-Alumosilicatglas mit Hilfe von ESCA und SIMS untersucht. Ausgehend von der Charakterisierung unterschiedlich präparierter Probenoberflächen wird der Nachweis des Ca²⁺-Einbaus in die Glasoberfläche aus Spurengehalten der KNO₃-Schmelzen erbracht. Die nach dem lonenaustausch ablaufenden Segregationsprozesse werden nach Langzeitlagerungen gemessen. Alkalianreicherungen an der Oberfläche sind mit Hilfe von Segregationsenthalpieunterschieden zwischen Oberfläche und Volumen interpretierbar. ESCA and SIMS investigations of ion-exchanged glass surfaces Concentration profiles near the surface of a K/Na ion-exchanged sodium aluminosilicate glass were investigated by ESCA and SIMS. Starting from the characterization of differently prepared sample surfaces, the incorporation into the glass surface of Ca²⁺ present as an impurity in the KNO₃ melt was demonstrated. The segregation developing after ion exchange was measured after storing for a long time. Alkali enrichment at the surface can be interpreted in terms of the difference in enthalpy of segregation between the surface and the bulk. Etude, par les méthodes ESCA et SIMS, de surfaces de verre traitées par échange d'ions Des profils de concentration proches de la surface ont été étudiés par ces méthodes sur un verre d'aluminosilicate de sodium ayant été traité par échange d'ions K/Na. La caractérisation de surfaces d'échantillons traitées différemment, a permis d'apporter la preuve de l'insertion, dans la structure de la surface du verre, de Ca²⁺ provenant de traces contenues dans les fontes de KNO₃. Les processus de ségrégation qui se déroulent après l'échange d'ions sont étudiés après de longues durées. Les enrichissements en alcalins à la surface peuvent être interprétés à l'aide de différences d'enthalpie de ségrégation entre la surface et la masse.
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    Fibroblast Response to Nanocolumnar TiO2 Structures Grown by Oblique Angle Sputter Deposition
    (Weinheim : Wiley-VCH, 2021) Kapprell, Uta; Friebe, Sabrina; Grüner, Susann; Grüner, Christoph; Kupferer, Astrid; Rauschenbach, Bernd; Mayr, Stefan G.
    Cells are established to sense and respond to the properties, including nano- and microscale morphology, of the substrate they adhere to, which opens up the possibility to tailor bioactivity. With this background, the potential of tilted TiO2 nanostructures grown by oblique angle sputtering to affect fibroblasts with particular focus on inducing anisotropy in cell behavior is explored. By depositing TiO2 at different oblique angles relative to the substrate normal, morphologies, columnar tilt angle, roughness, and distances between neighbored nanocolumns can be adjusted. To assess bioactivity of the resulting structures, L929-mouse fibroblasts are seeded in vitro on TiO2 nanostructured substrates. Angle-dependent movement and velocity distributions of the cells on differently tilted columns and a smooth reference sample are studied. Cell proliferation rates and cell areas are additional factors which provide information about viability and the well-being of cells. It could be shown that the local topography of the surface has an influence on the directed movement of the cells. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
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    Highly sensitive and specific detection of E. coli by a SERS nanobiosensor chip utilizing metallic nanosculptured thin films
    (Cambridge : Soc., 2015) Srivastava, Sachin K.; Hamo, Hilla Ben; Kushmaro, Ariel; Marks, Robert S.; Grüner, Christoph; Rauschenbach, Bernd; Abdulhalim, Ibrahim
    A nanobiosensor chip, utilizing surface enhanced Raman spectroscopy (SERS) on nanosculptured thin films (nSTFs) of silver, was shown to detect Escherichia coli (E. coli) bacteria down to the concentration level of a single bacterium. The sensor utilizes highly enhanced plasmonic nSTFs of silver on a silicon platform for the enhancement of Raman bands as checked with adsorbed 4-aminothiophenol molecules. T-4 bacteriophages were immobilized on the aforementioned surface of the chip for the specific capture of target E. coli bacteria. To demonstrate that no significant non-specific immobilization of other bacteria occurs, three different, additional bacterial strains, Chromobacterium violaceum, Paracoccus denitrificans and Pseudomonas aeruginosa were used. Furthermore, experiments performed on an additional strain of E. coli to address the specificity and reusability of the sensor showed that the sensor operates for different strains of E. coli and is reusable. Time resolved phase contrast microscopy of the E. coli-T4 bacteriophage chip was performed to study its interaction with bacteria over time. Results showed that the present sensor performs a fast, accurate and stable detection of E. coli with ultra-small concentrations of bacteria down to the level of a single bacterium in 10 μl volume of the sample.
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    Influence of substrate dimensionality on the growth mode of epitaxial 3D-bonded GeTe thin films: From 3D to 2D growth
    (Amsterdam [u.a.] : Elsevier Science, 2019) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, Bernd
    The pseudo-binary line of Sb2Te3-GeTe contains alloys featuring different crystalline characteristics from two-dimensionally (2D-) bonded Sb2Te3 to three-dimensionally (3D-) bonded GeTe. Here, the growth scenario of 3D-bonded GeTe is investigated by depositing epitaxial GeTe thin films on Si(111) and Sb2Te3-buffered Si(111) substrates using pulsed laser deposition (PLD). GeTe thin films were grown in trigonal structure within a temperature window for epitaxial growth of 210–270 °C on unbuffered Si(111) substrates. An unconventional growth onset was characterized by the formation of a thin amorphous GeTe layer. Nonetheless, the as-grown film is found to be crystalline. Furthermore, by employing a 2D-bonded Sb2Te3 thin film as a seeding layer on Si(111), a 2D growth of GeTe is harnessed. The epitaxial window can substantially be extended especially towards lower temperatures down to 145 °C. Additionally, the surface quality is significantly improved. The inspection of the local structure of the epitaxial films reveals the presence of a superposition of twinned domains, which is assumed to be an intrinsic feature of such thin films. This work might open a way for an improvement of an epitaxy of a 3D-bonded material on a highly-mismatched substrate (e.g. Si (111)) by employing a 2D-bonded seeding layer (e.g. Sb2Te3).
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    Ion Beam Assisted Deposition of Thin Epitaxial GaN Films
    (Basel : MDPI, 2017-6-23) Rauschenbach, Bernd; Lotnyk, Andriy; Neumann, Lena; Poppitz, David; Gerlach, Jürgen W.
    The assistance of thin film deposition with low-energy ion bombardment influences their final properties significantly. Especially, the application of so-called hyperthermal ions (energy <100 eV) is capable to modify the characteristics of the growing film without generating a large number of irradiation induced defects. The nitrogen ion beam assisted molecular beam epitaxy (ion energy <25 eV) is used to deposit GaN thin films on (0001)-oriented 6H-SiC substrates at 700 °C. The films are studied in situ by reflection high energy electron diffraction, ex situ by X-ray diffraction, scanning tunnelling microscopy, and high-resolution transmission electron microscopy. It is demonstrated that the film growth mode can be controlled by varying the ion to atom ratio, where 2D films are characterized by a smooth topography, a high crystalline quality, low biaxial stress, and low defect density. Typical structural defects in the GaN thin films were identified as basal plane stacking faults, low-angle grain boundaries forming between w-GaN and z-GaN and twin boundaries. The misfit strain between the GaN thin films and substrates is relieved by the generation of edge dislocations in the first and second monolayers of GaN thin films and of misfit interfacial dislocations. It can be demonstrated that the low-energy nitrogen ion assisted molecular beam epitaxy is a technique to produce thin GaN films of high crystalline quality.
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    Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures
    (London : Nature Publishing Group, 2016) Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd
    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.
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    Mikrodefektstrukturuntersuchungen oberflächennaher Schichten des Glases mit einer Bläschenmethode
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1978) Rauschenbach, Bernd; Hinz, Wilhelm
    In Veröffentlichungen der Autoren [1 bis 3] wurde eine unkonventionelle Methode vorgestellt, mit der Mikrodefekte in der Oberfläche und in oberflächennahen Schichten des Glases durch Bläschenbildung von im Glas implantierten Gasen nachzuweisen sind. In der vorliegenden Arbeit werden einige theoretische und praktische Aspekte dieser Methode aufgezeigt und einige Effekte zur Diskussion gestellt. Hierzu zählen insbesondere die Sichtbarmachung primärer und sekundärer Entmischungen, Anfangsstadien der Kristallisation in Gläsern, die Sichtbarmachung von Restspannungen an Mikrorissen sowie die latente Veränderung des Glases in der Umgebung von Rißspitzen (Ausbildung plastischer Zonen). Investigation of microstructural defects in the surface layers of glasses by a bubble method In several recent Communications [1 to 3] the authors have reported the development of an unconventional method by which micro-defects on the surface or in the surface layers of glasses may be revealed by the formation of bubbles from gases implanted in the glass. Some theoretical and practical aspects of this method are here considered further and some specific effects discussed. The following are particularly considered: making visible primary and secondary phase Separation, the initial stages of crystallization, revealing residual Stresses at micro-cracks and changes in the glass (plastic zones) around crack tips. Analyse de la structure des microdéfauts dans les couches superficielles du verre à l'aide de la « méthode des bulles » Les auteurs [1 à 3], dans de récentes publications, ont présenté une méthode peu conventionnelle permettant de déceler certains microdéfauts à la surface et dans les couches superficielles du verre, et qui consiste à provoquer la formation de bulles de gaz implantés dans le verre. On évoque quelques aspects theoriques et pratiques de cette méthode. Suit une discussion de certains effets typiques tels que la mise en évidence de démixtions primaires et secondaires, de débuts de cristallisation dans les verres, la mise en évidence de tensions résiduelles autour des microfissures de même qu'une modification latente du verre près de la pointe des fissures (formation de zones plastiques).
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    Nanostructures on fused silica surfaces produced by ion beam sputtering with Al co-deposition
    (Heidelberg [u.a.] : Springer, 2017) Liu, Ying; Hirsch, Dietmar; Fechner, Renate; Hong, Yilin; Fu, Shaojun; Frost, Frank; Rauschenbach, Bernd
    The ion beam sputtering (IBS) of smooth mono-elemental Si with impurity co-deposition is extended to a pre-rippled binary compound surface of fused silica (SiO2). The dependence of the rms roughness and the deposited amount of Al on the distance from the Al source under Ar+ IBS with Al co-deposition was investigated on smooth SiO2, pre-rippled SiO2, and smooth Si surfaces, using atomic force microscopy and X-ray photoelectron spectroscopy. Although the amounts of Al deposited on these three surfaces all decreased with increasing distance from the Al target, the morphology and rms roughness of the smooth Si surface did not demonstrate a strong distance dependence. In contrast to smooth Si, the rms roughness of both the smooth and pre-rippled SiO2 surfaces exhibited a similar distance evolution trend of increasing, decreasing, and final stabilization at the distance where the results were similar to those obtained without Al co-deposition. However, the pre-rippled SiO2 surfaces showed a stronger modulation of rms roughness than the smooth surfaces. At the incidence angles of 60° and 70°, dot-decorated ripples and roof-tiles were formed on the smooth SiO2 surfaces, respectively, whereas nanostructures of closely aligned grains and blazed facets were generated on the pre-rippled SiO2, respectively. The combination of impurity co-deposition with pre-rippled surfaces was found to facilitate the formation of novel types of nanostructures and morphological growth. The initial ripples act as a template to guide the preferential deposition of Al on the tops of the ripples or the ripple sides facing the Al wedge, but not in the valleys between the ripples, leading to 2D grains and quasi-blazed grating, which offer significant promise in optical applications. The rms roughness enhancement is attributed not to AlSi, but to AlOxFy compounds originating mainly from the Al source.
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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]
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    Plastische Deformation von mikroskopischen Rißspitzen im Glas
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1980) Rauschenbach, Bernd; Küchler, Roland; Hinz, Wilhelm
    Einleitend werden Betrachtungen zur mikroplastischen Deformation eines Glases angestellt und die Bedingungen für den elektronenmikroskopischen Nachweis dargelegt. Die beschriebenen Experimente geben Aufschluß über die Beschaffenheit des Rißgrundes, über Beziehungen zwischen Rißlänge und Länge der plastischen Zone sowie über das Rißwachstum. Mit Hilfe eines theoretischen Rißmodells werden aus dem Verhältnis von Rißlänge und Länge der plastischen Zone sowie aus der Rißverschiebung die Fließspannungen berechnet. Plastic deformation of microscopic crack tips in glass Considerations bearing on micro-plastic deformation in a glass and the conditions for their examination by electron microscopy are first discussed. The experiments described give information about the character of the crack field, the relation between the lengths of crack and plastic zone and crack growth. A theoretical model is used to calculate the yield stress from the relation between the lengths of crack and plastic zone and from the crack displacement. Déformation plastique des pointes de microfissures dans le verre Après quelques réflexions sur la déformation microplastique des verres, on passe en revue les conditions nécessaires au décèlement des fissures par microscopic électronique. Les essais décrits ici permettent d'obtenir des données sur la configuration du fond de fissure, sur le rapport entre la longueur de la fissure et la longeur de la zone plastique et sur la propagation de la fissure. Un modèle théorique permet de calculer les contraintes de fluage aussi bien à partir du rapport longueur de la fissure: longueur de la zone plastique qu'à partir du déplacement de fissure.
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    Research Update: Van-der-Waals epitaxy of layered chalcogenide Sb2Te3 thin films grown by pulsed laser deposition
    (Melville, NY : AIP Publ., 2017) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, Bernd
    An attempt to deposit a high quality epitaxial thin film of a two-dimensionally bonded (layered) chalcogenide material with van-der-Waals (vdW) epitaxy is of strong interest for non-volatile memory application. In this paper, the epitaxial growth of an exemplary layered chalcogenide material, i.e., stoichiometric Sb2Te3 thin films, is reported. The films were produced on unreconstructed highly lattice-mismatched Si(111) substrates by pulsed laser deposition (PLD). The films were grown by vdW epitaxy in a two-dimensional mode. X-ray diffraction measurements and transmission electron microscopy revealed that the films possess a trigonal Sb2Te3 structure. The single atomic Sb/Te termination layer on the Si surface was formed initializing the thin film growth. This work demonstrates a straightforward method to deposit vdW-epitaxial layered chalcogenides and, at the same time, opens up the feasibility to fabricate chalcogenide vdW heterostructures by PLD.
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    Structural Transitions in Ge2Sb2Te5 Phase Change Memory Thin Films Induced by Nanosecond UV Optical Pulses
    (Basel : MDPI, 2020) Behrens, Mario; Lotnyk, Andriy; Bryja, Hagen; Gerlach, Jürgen W.; Rauschenbach, Bernd
    Ge-Sb-Te-based phase change memory alloys have recently attracted a lot of attention due to their promising applications in the fields of photonics, non-volatile data storage, and neuromorphic computing. Of particular interest is the understanding of the structural changes and underlying mechanisms induced by short optical pulses. This work reports on structural changes induced by single nanosecond UV laser pulses in amorphous and epitaxial Ge2Sb2Te5 (GST) thin films. The phase changes within the thin films are studied by a combined approach using X-ray diffraction and transmission electron microscopy. The results reveal different phase transitions such as crystalline-to-amorphous phase changes, interface assisted crystallization of the cubic GST phase and structural transformations within crystalline phases. In particular, it is found that crystalline interfaces serve as crystallization templates for epitaxial formation of metastable cubic GST phase upon phase transitions. By varying the laser fluence, GST thin films consisting of multiple phases and different amorphous to crystalline volume ratios can be achieved in this approach, offering a possibility of multilevel data storage and realization of memory devices with very low resistance drift. In addition, this work demonstrates amorphization and crystallization of GST thin films by using only one UV laser with one single pulse duration and one wavelength. Overall, the presented results offer new perspectives on switching pathways in Ge-Sb-Te-based materials and show the potential of epitaxial Ge-Sb-Te thin films for applications in advanced phase change memory concepts.