Advanced Materials Science
Advanced Materials Science |
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The Field-of-Expertise Advanced Materials Science is an interdisciplinary network of researchers at the TU Graz in chemistry, physics, architecture, mechanical engineering, civil engineering, electrical engineering and geodesy who discover, characterize and model materials, functional coatings and components.
Due to the current COVID-19 situation, Advanced Materials Day 2020 will be held in a hybrid form: the posters will be physically displayed but the discussion will be done virtually.
Welcome 9:00 - 9:20 | |
| 09:00 - 09:20 |
Advanced Materials Day Online |
Metals and Alloys 9:20 - 10:10 | |
Evaluation of Quenching and Partitioning C20MnSi Steel microstructure Abstract: Quenching and partitioning is a novel heat treatment that has been proposed to give a good mixture of tensile strength and the total elongation by producing martensitic steel containing a certain amount of retained austenite (RA). The 2-step Q&P process enhances the stabilization of austenite by carbon enrichment through the segregation of the carbon from martensite to RA. The microstructure was investigated using LOM, SEM, EBSD, and XRD. The X-ray diffraction has been carried out in order to assess the retained austenite (RA%) volume fraction. It showed convergent RA fractions for different heat treatments with different quenching and partitioning temperatures. However, for different holding time in quenching and partitioning steps, recognizable differences in RA% can be observed. The mechanical properties obtained by Q&P reported for 20CMnSi steel at different Q&P temperatures showed comparable results. While, at different Q&P holding time, observable change in the mechanical properties is reported.
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Hydrogen embrittlement of advanced high-strength steels Abstract: Advanced high-strength steels have emerged interest in the automotive industry, because of the potential to reduce weight and to increase fuel efficiency. However, with increasing strength steels become prone to hydrogen embrittlement/stress corrosion cracking. Hydrogen absorbed during production or service can easily penetrate the components and lead to time-delayed brittle failure. The delay in time is crucial, because structural components have to be crack free for the whole lifetime of a car. Successful assessment strategies for advanced high-strength steels are still rare and experimental testing is very time consuming and expensive. Furthermore, hydrogen embrittlement tests are performed under controlled laboratory conditions for limited time and extrapolation to the lifetime of a car needs special consideration.
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Large Deformation Dislocation Density Based Crystal Plasticity Abstract: In dislocation density based crystal plasticity, the intersection events between dislocations moving on different slip systems are usually neglected. At large deformations, this is no longer appropriate.
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A finite elasto-plasticity model with orthotropic yield function and plastic spin Abstract: The concept of plastic spin, as presented by Dafalias, is the spin of the continuum relative to the material substructure. We concentrate on metal sheets in forming processes, in which pre-existing preferred orientations govern the orthotropic plastic behaviour. These orthotropic axes rotate with further deformations.
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Investigation the reversion transformation of deformation-induced Martensite Abstract: The reversion of deformation-induced martensite (DIM) was studied by investigating the microstructure evolution of the rolled austenitic stainless steel S304 during the heat treatment. The conventional light optical microscopy (LOM), electron microscopy (SEM), XRD, and magnetometry using ferritoscope have been used to characterize the microstructure and to estimate the phase fraction of microstructure constituents. Austenite with 2% ferrite compose the microstructure of the as-received S304 while during the rolling process ά and martensite formed inside the grains based on the stress assistance mechanisms. The ά martensite and ferrite are ferromagnetic phases detectable with a ferritoscope. According to the heat treatment result, the phase fraction of ferromagnetic phases decreases depending on the time and temperature of heat treatment. However light optical images reveal that the martensite phase fraction does not change significantly at 600°C and 700°C. Heat treatment at 800°C shows higher kinetics of reversion transformation for both ά and martensite. The microstructure of heat-treated samples at 800°C shows the completion of the recrystallization after 60 minutes. The recrystallized samples have much finer grain with a size of around 3µm than the as-received and rolled samples with a grain size of around 35µm.
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Microstructural Characterization of Thick Walled Ultra High Strength Steel S1100 Welded in Different Weld Positions Abstract: Using ultra high strength structural steels enables not only light weight constructions, by reducing sheet thickness and thereby weight and filler material but also contributes to achieving current challenges in different fields of technology. Due to their accurately tuned chemical composition and precisely controlled thermo-mechanical processes during the production, a very efficient microstructure with respect to strength and ductility is maintained. Various strengthening mechanisms are applied to achieve the desired strength, ductility, toughness and fatigue properties.
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A hybrid continuum model for dynamic concurrent atomistic-to-continuum methods Abstract: Dynamic concurrent atomistic-to-continuum methods commonly employ either a dynamic or a quasi-static continuum model. Both of these approaches have advantages and drawbacks which render their applicability problem-specific. We present a hybrid continuum model, which has been developed to combine the advantages of both approaches while removing the drawbacks. This novel approach is based on the superposition of a dynamic and a quasi-static subproblem and, thus, is limited to linear elastic continua. We apply the approach to a prototypical representative of the concurrent atomistic-to-continuum methods and namely, the coupled atomistic and discrete dislocation (CADD) method.
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Microbiologically influenced corrosion (MIC) of steel – a study using correlative SEM, EDX and Raman microscopy Abstract: Microbiologically influenced corrosion (MIC) is responsible for 20% of all corrosion damage [1]. In this context, there is great interest in understanding MIC especially, since it has been shown that some microbes slow down the rate of corrosion [2], while others speed it up [3]. During experiments in the Koralmtunnel, iron-oxidizing bacteria were found, to be part of a MIC causing, microbial community. SEM pictures shows typical structures produced by this bacterial culture in figure 1.
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3D - Printing 10:10 - 10:55 | |
Influence of bed surface on the mechanical performance of CF-PA6 parts printed by FFF Abstract: The objective of this study was to gain an understanding of the influence of different materials commonly used as printing bed on the mechanical performance of carbon fiber reinforced polyamide-6 (CF-PA6) parts 3D-printed by Fused Filament Fabrication (FFF). This analysis was based on finding an appropriate relationship between temperature evolution, ultimate tensile strength (UTS) and resulting microstructure. Results showed that there is a loss of approximately 30% in UTS when changing the bed surface from glass to aluminum. The use of up to four Kapton layers (0.35 mm thickness each) between the 3D-printed part and the aluminum bed did not result in any significant differences with respect to the mechanical performance. A severe interlayer delamination was observed on specimens printed in the aluminum bed, which did not occur when printing on glass. Although temperature gradients during the process remained unchanged regardless of the bed surface, the cooling rate on the 3D-printed part after the process was 36% higher when printing on an aluminum bed, which could have increased the content of residual stresses.
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Microstructure analysis of additive manufactured CF-PA6 parts under consideration of different consolidation parameters. Abstract: Additive manufacturing is becoming increasingly important in field of component design. In order to enhance the mechanical properties of 3D printed components, load-oriented Continuous fiber Composite Materials (CFC) are used. A poor parameter selection for the manufacturing process of 3D-Printed CFC components leads to an inhomogeneous distribution of the fibers and increased occurrence of cavities in the matrix material [1]. These imperfections can be described by deconsolidation occurring in the laminate and indicate an insufficient consolidation, temperature management over time in the process. This research presents the problem analysis and shows possibilities for an improvement of the 3D-Printed Carbon Fiber Reinforced Polyamide-6 (CF-PA6) material by: First, printing specimens of the used material with different parameter settings and second, conducting material tests in combination with microstructural analysis. By preparing microsections of the specimens, a closer look inside the structure of the material is obtained which defines the basis for further development in terms of its homogeneity. For the printing process, the Continuous Filament Fabrication (CFF) system from MarkForged (MF) with a self-developed controller board and an open source software is used.
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Expanding 3D Nano-Printing Performance by Blurring the Electron Beam Abstract: FEBID is a mask-less direct-write fabrication process where surface adsorbed precursor molecules are dissociated and thereby immobilized upon irradiation with a focused electron beam. Aside from the additive character with minimal demands on the substrate materials and morphologies, this technology allows the fabrication of freestanding, 3-dimensional architectures with feature sizes down to the sub-20 nm range. As FEBID based 3D nanoprinting[1] is realized by the slow lateral movement of the electron beam, the design flexibility is very high, which opens up entirely new possibilities for e.g. optical metamaterials, plasmonic structures and advanced scanning probe microscopy tips[2]. The long term aim of this work is to tune the 3D-FEBID process in a way, which allows the deposition of functional electromagnetic helices, which require long, freestanding and shallow inclined segments. While beneficial for other applications such as 3D plasmonics, the small nanowire diameters, obtained by standard 3D-FEBID conditions, entail highly growth instabilities due to their high thermal resistance, which lead to heating issues in the beam impact regions. Based on previous studies with defocused electron-beams[3], we studied the controlled introduction of a beam blur for 3D-FEBID. Our results reveal, that the introduction of a defocused e-beam can stabilize the spatial growth in 3D space (precision), while growth rates strongly increase (efficiency) and all unwanted artifacts are minimized (co-deposits and / or structural collapse). At the same time, blurred beams not only allow an on-purpose tuning of branch diameters but also can be used for shifting the height/width aspect ratio within certain ranges. By that, this study lies the foundation for the originally aimed fabrication of functional electromagnetic helices, which will be in focus in near future.
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Electron beam freeform fabrication of NiTi shape memory alloys Abstract: Recently, Shape Memory Alloys (SMA) have been fabricated by wire-based electron beam additive manufacturing technique for the first time1. Despite successful, no attention was paid to the effect of processing parameters on the structural aspects (height and width), implications on welding features (dilution), and compositional variations (Ni evaporation). The understanding of the aforementioned aspects shed light over the fabrication, indicating how each of the processing parameters affects these features. For this purpose, the current work addresses, by means of Design of Experiments using Box-Behnken Design (BBD), how beam current, welding and feeding speeds affect the stability of the built part and its properties. Based on these findings, one can propose a suitable combination of parameters to deposit a bulky multi-track structure, aiming further mechanical assessment.
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In situ structural analysis of AlSi$_{10}$Mg for additive manufacturing – from powder to thermally treated parts Abstract: Printing three-dimensional, robust metallic structures via laser beam melting of alloy powders is a rapidly growing industry branch. Manufacturers of such parts strive for optimizing their processes, not only to improve material properties, but also to enhance the interchangeability of building platforms and thus, their economic flexibility. However, the number of critical parameters for 3-D printing is large and most simulations or macroscopic tests do not paint a broad enough picture about the outcome of a recipe. As-built samples from the same powder alloys but from different manufacturing batches with altered process parameters differ in mechanical properties due to the grade of intrinsic thermal treatment they experience in the respective laser-melting process. Differential scanning calorimetry and X-ray diffraction are prominent techniques used to provide information on transitions and crystallinity in the material before and after additional treatments, but the results are often inconclusive with respect to morphological changes. Through in situ heating experiments in TEM, applying EDXS and EELS for structural and elemental analysis, we aim to bridge this gap. We therefore studied the micro- and nanostructure of an AlSi$_{10}$Mg – a high-hardness lightweight alloy with well-known casting properties that is of great interest for additive manufacturing.
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Friction Surfacing as an alternative additive manufacturing technique for titanium alloys Abstract: The most used additive manufacturing technologies, like powder bed fusion or wire arc additive manufacturing, are all fusion based processes, meaning that the melting temperature of the metal is reached during the layer-by-layer production. This frequently results in undesired microstructural features, such as pores, inclusions, high residual stresses induced by solidification and coring effects. Due to this, a fusionless solid-state additive manufacturing method is in high demand. One process that fulfills this requirement is the Friction Surfacing, which uses a rotating metallic consumable rod to generate heat by friction and plasticizes the materials, without melting. Since this a relatively new technique, not many material combinations have been investigated, in particular titanium alloys, remaining a vastly unexplored application area. Therefore, the aim of this work was to firstly deposit a single layer of Ti-64 by friction surfacing with 12 mm rods and obtain information about the microstructure and mechanical properties. The results were considered to determine the feasibility of a double layer deposition (meaning that two single layers are consecutively deposited and centered on top of each other). Results showed that the double layer formation was not as stable as the single layer, since the decreased contact surface demanded longer times for shear layer formation at the beginning. As for the microstructure, the double layer showed a grain enlargement in the second layer and some porosity in the transition zone. The hardness of both second and first layer was increased by the reduction in grain size and formation of oxygen-stabilized regions, consisting of the α-phase.
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Expanding Capabilities of Focused Electron Beam Based 3D Nano-Printing: From Meshes Towards Closed 3D Nano-Architectures Abstract: Focused electron beam induced deposition (FEBID) is an aspiring technology for next-generation direct-write fabrication on the nano-scale. While FEBID-based fabrication of freestanding, 3D mesh-like nano-architectures has already reached a high level of precision, predictability and reliability[1,2], we now expand those single wire designs towards closed and semi-closed 3D nano-architectures. This opens up numerous possibilities as well as new challenges that will need further research in the future. Although 3D growth of meshed objects is meanwhile well understood, the expansion to closed basic building blocks namely vertical walls, rises new challenges. In particular, beam induced heating was found to entail partly unexpected effects at exposed regions such as edges or corners. Hence, we currently focus on the fundamental understanding of the growth behaviour for vertical walls, which will form the basis for any further expansion concerning their shape (e.g. circles or triangles) and / or their inclination angles to enable highly precise fabrication of closed and semi-closed 3D nano-architectures. In a combined approach between experiments and simulations, we develop a growth model, which in turn can compensate for such drawbacks to approach the intrinsic precision limits during 3D-FEBID. This will lead to predictable and reproducible fabrication of even complex 3D nano-architectures as essential element on the route towards a generic 3D nano-printing technology for future applications in various fields of research and development.
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Porous Materials 11:15 - 12:00 | |
Investigation on the influence of alkyl ligands of zinc xanthate complexes on the formation and porosity of ZnS thin films Abstract: Many metal sulfides show great interest in various applications including luminescent devices, sensors, solar cells and many more. Among the various routes towards metal sulfides, we focus on a single source precursor route using metal dithiocarbonates, also known as metals xanthates. These are metal-organic compounds exhibiting a sulfur-metal bond, which decompose at relatively low temperatures (<200°C) resulting in highly pure metal sulfides via a mechanism called Chugaev elimination. Another advantage is the ability to control their properties (decomposition temperature, solubility) by changing the structure of the xanthate ligand and/or adding additional ligands.[1,2]
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Deposition of Ion Conductive Membranes from Ionic Liquids via Initiated Chemical Vapor Deposition Abstract: Ionic liquids (ILs) are salts that are liquid below 100°C, many are still in their liquid state at room temperature. Their high proton or anion conductivity makes ionic liquids highly attractive for a large variety of new electrochemical applications. For many applications, however, it would be much easier to handle ILs in a solid state, in form of a membrane.
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Insights into dealloying from in-situ magnetometry Abstract: The formation of nanoporous metals via corrosion of one component from a binary alloy is commonly referred to as 'dealloying'. This dealloying synthesis route allows to produce a plethora of different nanoporous metal systems with manifold possible applications in catalysis, sensing, actuation, biomedicine, or energy storage. Although a good basic understanding of the dealloying process has been acquired from kinetic Monte Carlo (KMC) simulations[1], mechanistic details, such as the less noble metal retention, remained mostly unexplored. Using cobalt as a magnetic sacrifical element makes SQUID magnetometry a sensitve method to study the dealloying process. In-situ measurements of corrosion charge and magnetic moment allow to separate the dealloying process into two distinct phases of pore growth. Evolution of coercivity revealed a transition from collective ferromagnetism to superparamagnetism of small alloy clusters, which gradually evolve in the dealloying process. This evolution of clustered alloy regions is also prediced by our KMC simulations. In addition, SQUID magnetometry reveals how these residual alloy clusters can be altered via the corrosion parameters, allowing the production of tailor-made magnetic nanostructures[2].
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In situ monitoring of the formation and orientation of mesopores in H1-ePt films by GI-SAXS during templated electrodeposition Abstract: The electrochemical deposition and growth of nanostructured platinum and palladium films was investigated in situ with Grazing Incidence Small Angle X-ray Scattering (GISAXS) - a nondestructive surface-sensitive technique for structure determination in the nm-regime. The growth of the films was templated using hexagonal (H$_1$) lyotropic liquid crystalline phases of non-ionic surfactants, which are in our case a ternary mixture of aqueous 0.2 M H$_2$PtCl$_6$ and C$_{16}$EO$_8$ (50:50 wt.%) or a quarternary mixture of 12 wt.% (NH$_4$)$_2$PdCl$_4$ , 47 wt.% C$_{16}$EO$_8$ , 2 wt.% heptane and 39 wt.% water.
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Revealing the photo-triggered structural dynamics of photo-responsive Metal-Organic Frameworks grown on oriented heteroepitaxial ceramic thin films Abstract: Abstract: At present, most developments based on microelectronics, sensing and optical devices rely on the technology of thin-film fabrication. The ever-growing field of Metal-Organic Frameworks (MOFs) has been shown to have a huge potential in various of these subjects, especially when deposited as thin films on solid substrates. Yet, the development of automated deposition techniques for MOF thin film fabrication in high yields comprising a defined orientation still remain a challenge in this field.
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Functional Biodegradable Polymer-based 3D Scaffolds: Fabrication, Characterization and Application in Tissue Engineering Applications Abstract: Three-dimensional (3D) scaffolds have been widely used for the reconstruction and restoration of various anatomical defects of complex organs and functional tissues. The biomaterial scaffold enables cell attachment, proliferation, migration, transport of body fluids, and reconstruction of bones, nerves, vessels, etc., while providing a platform for the reconstruction of defects. Scaffolds integrated with all these demanding features can be fabricated by combining biodegradable polymers and the advanced 3D bioprinting technique, which is capable of producing custom scaffolds with high structural complexity and design flexibility for soft (e.g. cartilage) and hard (e.g. bone) tissue engineering applications. This work presents a generic method for the design of porous scaffolds from the water-soluble/dispersible polysaccharides (e.g. nanofibrillated cellulose) or thermoplastic polymer like starch esters or polycaprolactone. 'Inks' with different viscosities from polysaccharides/thermoplastic polymers were formulated and used to generate differently shaped self-standing structures by the combination of freeze-drying and direct ink writing 3D printing technique[1, 2]. Besides their excellent biocompatibility with human bone tissue derived cells (e.g. bone or stem cells), the scaffolds showed controlled degradability, dual-porosity, and long-term mechanical and dimensional stability in biofluids. The latter features of the polysaccharides-based scaffolds were improved by the physical cross-linking via dehydrothermal treatment or by chemical cross-linking with polycarboxylic acids. The simple and straightforward avenue proposed here for the design of polysaccharide-based fibrous or thermoplastic inks and multi-porous scaffolds from the biodegradable polymers pave the way for the development of implantable and cell-laden complex 3D biomaterials for tissue regeneration and regenerative medicines.
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Implications of pulp fiber porosity on material modelling Abstract: Pulp fibers are extracted out of the "lamellar" wood structure by rough mechanical and chemical treatment. A side effect of these treatments is that in the fiber wall locally material is removed or delaminates. In combination with commonly applied moisture changes this damaged regions evolve to a porous space. Porous material which is eventually filled with water behaves especially in compression quite differently. While modelling techniques of saturated porous material (poroelasticity) is an established research field in civil engineering, we adopt this concepts of poroelasticity to identifiy an increased relaxation behavior while fibers are immersed in water.
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Organic Electronics and Sensors 12:00 - 12:30 | |
Laboratory of Applied Materials for Printed and Soft electronics (LAMPSe) Abstract: Laboratory of Applied Materials for Printed and Soft electronics (LAMPSe) investigates soft/stretchable/conformable conductive materials with main applications in sensing, actuation and biomedicine. The focus of our lab includes laser-induced carbons, conducting polymers, organic semiconductors, nanocomposite functional materials, and stimuli-responsive polymers and interfaces. Our research is carried out with modern fabrication and deposition techniques including laser induced pyrolysis, inkjet and screen printing, solution and vacuum based methods with the aim to create novel wearable, skin-conformable devices. Temporary tattoo paper is adopted as an unconventional substrate to build up transferable body compliant devices, which establishes a stable and long-lasting interface with the skin.[1] This approach is advancing to become state-of-the-art, overcoming some limits of existing technologies, as in the case of skin-contact electrodes made of thin film of PEDOT:PSS.
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pH Sensor Tattoo Abstract: The design of a flexible pH sweat sensor that is bio-compatible, has skin-alike elasticity and is sustainable in acidic environments is a challenging task. Current trends in research tend to an organic compound consisting pH sensor for medical diagnostic applications. But so far the manufacturing process of such sensors is not feasible nor scalable. In this study a novel all-polymer sensor will be presented that address all the challenges mentioned above and use a manufacturing process that is direct and scalable. Polymer electrodes were screen printed on temporary tattoo paper and coated with a bio-compatible pH responsive hydrogel via initiated Chemical Vapor Deposition. The pH responsive hydrogels absorbed different amounts of artificial sweat depending on the pH. Upon swelling of the gel film the conductivity was increasing and the resistance was decreasing which was measured by means of resistance measurements through impedance spectroscopy. The use of temporary tattoo paper as substrate material will have two major advantages. One being the fact that tattoo transferred hydrogels will be in intimate contact with the skin leading to more precise and faster detection of the pH of the skin. The other being that the printed polymer electrodes can directly act as read out terminals for the hydrogels response. For the first time tattoo electrodes were coated with a responsive material via a vapor-based deposition technique. This novel combination enables for a very thin sensor, excellent conformal adhesion to the skin and great pH sensitivity. All through the use of direct and scalable methods, which in combination open the door for a wide range of possible interesting applications.
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Phase behaviour and order in an asymmetric Benzothieno-benzothiophene derivative Abstract: 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzo-thiophene (Ph-BTBT-10) is an organic semiconductor, which’s properties are interesting for the use in OFETs, due to a high charge carrier mobility in thin films. Due to its assymetric shape and combination of a rigid core, consisting of a Benzothieno-benzothiophene (BTBT) and its different end-groups (decyl and phenyl), complex phase transitions to liquid crystalline phases can be observed. Here we present a transitions to a new polymorphic phase, when prepared via physical vapour deposition, which, surprisingly, only becomes stable at film thicknesses above 12 nm. The structure of this polymorph is solved with a combined experimental/ computational approach, merging Grazing Incidence X-ray Diffraction experiments with Molecular Dynamics simulations. In further work, a study on the influence of order in such an asymmetric molecule is undertaken, revealing a specific kind of disorder due to the missing invariance of the molecule being stacked in either a head-to-head or a head-to-tail arrangement. Such disorders are introduced into the molecules by fast processing methods, far away from thermodynamical equilibrium, e.g. Thermal Gradient Crystallization or Bar-assisted Meniscus Shearing.
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Synthesis and Characterization of Perylene-Linker-Perylene Triad Structures as Non-Fullerene Acceptors for Organic Solar Cells Abstract: Perylenes are a material class which can be implemented as acceptor in organic solar cells (OSC) due to well-suited and easily tunable optoelectronic properties. So far, research is focused mainly on perylene diimides and solar cells with efficiencies of ~10% could be fabricated. On the other side, perylene monoimides got less attention although they offer another open site for substitution and thus more possibilities for chemical modification. Hereby, also the too pronounced π-π stacking of perylene diimides can be tackled by twisting the molecule and positive properties like good solubility and absorption behavior are maintained.
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Cold crystallization of the organic n-type small molecule semiconductor 2-decyl-7-phenyl-[1]benzothieno[3,2- b][1]benzothiophene S,S,S´,S´-tetraoxide Abstract: The asymmetric n-type BTBT derivative 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene S,S,S',S'-
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Thin-film formation of 2,7-bis(2(2-methoxyethoxy)ethoxy) benzo[b]benzo[4,5]thieno[2,3-d]thiophene (FD44) Abstract: Organic semiconductors are promising for thin-film transistor applications as they potentially offer distinctive advantages over their inorganic counterparts particularly in terms of its properties, processing techniques and cost-effectiveness. Small molecules with extended aromatic core and solubilizing long chains are budding candidates for solution-processed organic semiconductors. Here we investigate the crystal structure solution and film-forming properties of FD44, which is a [1]benzothieno[3,2-b]benzothiophene (BTBT) derivative. When we consider the structural aspect of the BTBT core, molecules arrange in a herringbone type packing which facilitates 2D carrier transport properties. The thin films were solution-processed by spin coating and drop-casting techniques from solvents with different boiling points. Chloroform and tetrahydrofuran are the low boiling point solvents used for the thin film preparations whereas chlorobenzene, 1,2-dichlorobenzene, o-xylene and cyclohexanone are the high boiling point solvents used. Morphologies of the thin films were different depending upon the type of solvent used for their fabrications. We obtained good quality films from the preparations and their crystal structure investigations were performed using both in house X-ray equipment and synchrotron. The crystal structure of FD44 was resolved from the single crystal and the Grazing Incidence Xray Diffractions(GIXRD) were performed to determine the crystallographic structure within the thin film. All the observed peaks in the films were mapped well by the single crystal lattice. That is, the structure in the thin films was identical with that in the single crystal. Also, monolayer investigations of FD44 films were carried out in various solvents and the results were analysed using X-ray reflectivity measurements in order to understand its monolayer formation at the substrate surface and thereby determine its polymorph formation due to the presence of a surface during the crystallisation process.
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Gründungsgarage 13:20 - 13:30 | |
Gründungsgarage: The Academic Startup Accelerator! Abstract:
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Inorganic Materials 13:30 - 14:10 | |
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Studies of Ionizing Radiation Effects in NanoScale Technology Nodes for High Energy Physics Experiments (SIRENS) Abstract: Radiation effects on electronic devices have been in research focus for over four decades. New degradation mechanisms are being observed with new device developments and in particular with scaling of the integrated circuits. The SIRENS project focuses on radiation-induced device degradation in CMOS processes with high dielectric constant (high-K) gate stack. Specifically the planar bulk 28 nm and 40 nm MOS transistors are investigated. The high-K gate stack coupled with severe device scaling is going to be studied in terms of geometry-dependence and the dominant locations of interface and oxide traps. The radiation effects will be modelled for device-level simulation.
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Stability of lead-based perovskite solar cells with respect to structural changes Abstract: Perovskite solar cells are a rising star in the field of thin film photovoltaics. Their efficiency increased to over 25% within hardly more than a decade and has thus reached values comparable to those of crystalline silicon solar cells. The success of perovskite solar cells lies in the rare combination of easy, low-temperature processability and excellent photovoltaic properties. However, serious challenges are faced when it comes to their long-term stability. Degradation can be induced by almost all external factors, such as light, oxygen or humidity. The degradation mechanisms can be complex and are not yet fully understood. This thesis' work takes a look at the response of perovskite solar cells to several different external stressors, most importantly light, and investigates the role of the hole transport layer. The stability behaviour under illumination is investigated for an organic and an inorganic hole transport layer.
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Particle losses in a porous tube diluter for different nanoparticle materials and generators Abstract: Particle emissions are the second largest contributor to air pollution [1], therefore particle concentration levels have to be monitored. Although several measurement devices are available, in most cases aerosol sampling is necessary. Diluters are used to decrease the particle concentration and shift it to a range, that is suitable for the measurement instrument. One can obtain the original concentration by multiplying the measurement results with the dilution factor of the system.
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Charging mechanisms of nanoporous electrodes in hybrid supercapacitors Abstract: Hybrid supercapacitors combine the positive properties of batteries and electric double-layer capacitors (EDLCs). In these devices, one electrode stores charge at electric double-layer (EDL), generally made from nanoporous carbons, and the other is a high capacity battery-like electrode. We work with two types of hybrid supercapacitors. First where lithium based battery electrode is used in organic electrolytes (high reachable voltage) and the second where iodine based battery electrode is used in aqueous electrolytes (low reachable voltage), while keeping the same EDL electrode made from high surface area carbon material.
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Thermocrystals: Calculation and preparation of coherent phonon sources Abstract: In collaboration with the materials center Leoben, this projects goal is to computationally design and physically produce thermocrystals that can be used as coherent phonon sources, filters and detectors. Thermocrystals are nanostructured semiconductor alloy crystals which allow to manipulate heat similar as light waves are manipulated by lenses and mirrors. For the fabrication of such systems, plasma-enhanced atomic layer deposition (PE-ALD) is used, as it allows the control in layered structures down to monolayers. After fabrication, samples are analyzed using X-ray diffraction, ellipsometry, UV-Vis spectroscopy, atomic force microscopy and x-ray photoelectron spectroscopy.
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Piezoelectricity of zinc oxide thin films deposited by plasma enhanced atomic layer deposition Abstract: Investigation of the piezoelectric response of zinc oxide films prepared by plasma-enhanced atomic layer deposition (PE-ALD). The influence of the substrate as well as the substrate temperature during deposition is investigated. Films deposited on flexible polyethylene terephthalate (PET) generated higher piezoelectric current (> 1.8 nA) compared to films deposited on glass (> 0.3 nA) due to substrate bending. The generated piezoelectric current is enhanced at increased temperatures due to improved growth along the (002) crystallographic orientation.
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(Bio)Polymers 14:10 - 14:50 | |
Effect of the blend ratio on mechanical properties and morphology of elastomer-thermoplastic blends Abstract: Blending of raw polymeric components is a well-established strategy to design new materials. This conveniently allows the combination of favorable properties of different polymers.
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Extending the properties of polysaccharides by polymer analogous reactions Abstract: As a very diverse, somewhat arbitrarily defined group of biomolecules, polysaccharides fulfil significant biological functions, ranging as far as from peptidoglycans in bacteria, to glycogen in humans. Chemosynthetic derivatization of existing, biologically synthesized polysaccharides can extend their given properties, can allow for a better understanding of their biological function, and can potentially lead to new applications. The most often encountered functional groups in polysaccharides are hydroxyl, carboxyl, ester, amide, ether, and acetal groups, among others. If the polymer backbone is to be preserved, chemical derivatization is therefore mostly concerned with the formation of ethers, esters, carboxyls, acetals, amides, amines or imines. Performing well controlled and chemically defined polymer analogous reactions with polysaccharides is complicated by: a) the presence of multiple functional groups and chiral centers, b) variations in the molecular weight distribution depending on the source and extraction method, c) accessibility and solubility, d) chemical stability and purification. By a carful choice and control of the reaction and purification methods however, useful polyfunctional derivatives of polysaccharides can be obtained.
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Detecting Nanoplastic Particles using Correlative Microscopy Abstract: Nowadays “microplastics” (MPs) is an already well-known term and micro-sized particles are increasingly found in several consumer products [1]. Moreover, effects of micro- and nanoplastics (NPs) on human health have been investigated and discussed [2]. In this study, the focus is pointed to MPs smaller than 1 µm, with a specific focus on particles in the scale of a couple of 100 nm, which are referred here as NPs. A correlative approach between scanning electron microscopy (SEM, high resolution) and Raman microscopy (chemical identification) was tested to meet the challenges of finding and identifying these small particles. For this purpose standardized polystyrene (PS) beads were mixed into various environments in different concentrations, ranging from ideal (distilled water) to realistic (sea salt, human amniotic fluid), to proof the detection limit of NPs with the so called RISE (Raman Imaging and Scanning Electron microscopy) system [3]. Promising results exhibit detection limits of 2·10-3 µg/L (distilled water), 20 µg/L (sea salt) and 200 µg/L (human amniotic fluid).
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Advanced Functional Surfaces from Biodegradable Materials Abstract: Owing to their abundance and simple manufacturing process, the biodegradable polysaccharides (PS) and polyesters like polycaprolactone (PCL) have great potential to be used in advanced applications such as functional wound dressings and textiles, biocompatible coatings or patterned thin films. For many of these functions surface properties and the interactions at the PS or PCL interfaces are crucial. By a detailed understanding of wetting, adsorption, adhesion, surface morphology and internal structure, PS/PCL materials and coatings with the desired properties can be created. Spin-coated thin films of PS or PCL a platform that can be used to elucidate these surface phenomena. Besides their defined composition and morphology, they can be characterized with, and employed in, modern surface analytical methods such as a quartz-crystal microbalance, surface Plasmon resonance, etc. These films can further be lithographically structured and serve as a basis for functional layers in optical sensors for the detection of DNA or as anticoagulant surfaces[1,2]. On the other hand, the biological efficacy of many charged polysaccharides or proteins can also be exploited in the coating of PS or polycaprolactone. This is demonstrated by the anticoagulant and cell growth properties of PS or PCL or combination of these two surfaces. Highly functional wound dressings that are antimicrobial, super-absorbing and analgesic are another example where basic and applied know-how on PS materials are leading to innovative products[3]. In this presentation an overview of current achievements in these fields of research will be given.
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Ultrasonic joining of additively manufactured stainless steel 316L and Polyetheretherketone Abstract: The Ultrasonic Joining (U-Joining) process is a novel friction-based joining technique capable of producing through-the-thickness reinforced hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. The process feasibility has been successfully demonstrated to join injection-molded Ti-4Al-6V and extruded unreinforced and glass-fiber-reinforced Polyetherimide structures; however, there is an unexplored field concerning U-Joining of additively manufactured (AM) parts. The aim of the investigations is to demonstrate the feasibility of U-Joining to assemble AM metal and polymer parts by investigating the case-study base materials stainless steel 316L and Polyetheretherketone (PEEK). Firstly, the 316L and the PEEK parts were produced by Powder Bed Laser Fusion (PBLF) and Fused Filament Fabrication (FFF) processes, respectively. Secondly, the joining parameters were optimized through Design of Experiments (DoE). Finally, the influence of the surface roughness of as-printed AM metal parts on the quasi-static mechanical performance of metal-polymer single-lap hybrid joints was evaluated to enable the understanding of joint formation and strength. The obtained results proved the feasibility of U-Joining to assemble AM metal and polymer through-the-thickness reinforced parts.
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E-Modulus of Geopolymer Mortar over Time and its Influencing Factors Abstract: Ordinary Portland Cement(OPC)-based concretes are widely used for wastewater infrastructure in the sewage systems. Aggresive environment in sewage systems causes the deterotion of calcium component in OPC-based concrete. This problem is the main issue in concrete durability that affects the performance and maintenance costs. With quite low calcium rate, Geopolymer (GP)-based binders can be an alternative material for OPC. Within this project, OPC-based concrete sewage infrastructure is covered with GP. Although GP has satisfying mechanical properties, due to its cost, a hybrid system OPC-GP system is developed. For this purpose, OPC-based concrete is covered with GP-mortar as a barrier, firstly to protect substrate from aggressive environment and secondly to be a load-carrying component. In order to have an efficient bonding between OPC-GP system, the properties of GP-mortar were investigated with two different curing conditions. For this purpose: Moisture content, E-Modulus and early-creep behaviour of GP-mortar was investigated on prismatic (40x40x160 mm) samples.
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Surface Science 14:50 - 15:20 | |
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Energy dissipation on Dirac and semimetal surfaces Abstract: At finite temperatures the ideal zero-Kelvin behaviour of Dirac materials is perturbed and scattering processes via electron-phonon (e-ph) coupling can give rise to energy losses. Atom-surface scattering provides a sensitive probe to determine the surface phonon energies and energy dissipation considering that electronic transport is coupled to the motion of the ion cores (phonons).
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Surface structure search for Organic/inorganic interfaces Abstract: Studying the electronic structure of organic monolayers on inorganic substrates requires knowledge about their atomistic structure. Such monolayers often display rich polymorphism arising from diverse molecular arrangements in different unit cells. The large number of possible arrangements poses a considerable challenge for determining the different polymorphs from first principles.
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Search for New Polymorphs by Epitaxial Growth Abstract: The formation of unknown polymorphs due to the crystallization at a substrate surface is frequently observed. This phenomenon is much less studied for epitaxially grown molecular crystals, since the unambiguously proof of a new polymorph is a challenging task. The multiple epitaxial alignment of the crystallites together with the presence different polymorphs do not allow simple phase identification. We present grazing incidence X-ray diffraction studies on conjugated molecules like PTCDA, pentacene, dibenzopentacene and of dicyanovinylquater-thiophene grown by physical vapor deposition on single crystalline surfaces like Ag(111), Cu(111) and graphene. A new method for indexation of the observed Bragg peaks allow a determination of the crystallographic unit cells so that the type of crystallographic phase can be determined. Additionally, epitaxial relationships between the epitaxially grown crystallites and the single crystalline surfaces are determined.
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Exploring polymorphism in phenoxazine and S-naproxen thin films on silica Abstract: Research on polymorphism played over the last decades an important role in various scientific fields like materials science, pharmaceutics etc. Especially, the behavior of various materials to form polymorphs close to surfaces is an essential area under investigation. Phenoxazine, a well-known heterocycle compound, is mainly used as a parent molecule for different application in organic electronics and pharmaceutics. [1] Since no crystal structure is known so far, here one crystal structure is solved by single crystal X-ray diffraction from extended crystals. The phenoxazine crystallization in thin films from tetrahydrofuran solutions revealed an additional 2nd polymorph. The structure solution was obtained by advanced indexation methods merged on reciprocal space maps and following Molecular Dynamic simulations. Within the thin films, selection between the two phases results from the crystallization process. Drop casting on the flat silica surface, ends in the formation of both phases but with a tendency to form the bulk phase, by decelerating solvent evaporation. The fast spin coating solely gives the kinetically driven 2nd phase.
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Selecting drug polymorphs by epitaxy using tunable templates Abstract: The presence of a surface during the crystallisation process can cause the appearance of unknown crystal structures of molecular materials. These polymorph structures show different molecular packings; as a consequence a variation of application relevant properties appear for pharmaceutical molecules appear like stability and solubility. This project is focussed on the epitaxial growth of pharmaceutical molecules. The used substrates are templates with adjustable geometry, so that lattice matching of the substrate and of the overgrown pharmaceutical crystals is possible. The tuneable templates will be prepared by solid solutions of rod-like conjugated molecules (e.g. phenothiazine and iminostilbene), fabricated by a monolayer on atomically flat silicon wafers. The goal of the project will be the selective preparation of defined polymorphs of carbamacepine by epitaxial growth and in a subsequent step the discovery of unknown polymorphs of carbamacepine or recorcinol by epitaxial growth. Two different types of sample preparation methods will be used: solution processing (spin coating, dip coating, drop casting) and physical vapour deposition. While physical vapour deposition is a highly defined process, where the preparation of the templates and the crystallisation experiments is performed in subsequent steps, solution processing is a rather joint preparation method for templates and pharmaceutical crystals. Details of the sample preparation process like the type of solvent, solvent evaporation rate, concentration of the solution have to be varied and optimized. The thin films will be investigated in terms of their structural properties. The morphology will be studied by a combination of optical microscopy and atomic force microscopy. The crystalline properties will be studied by grazing incidence X-ray diffraction using synchrotron radiation. The correlation of morphology with crystalline properties will be performed by lattice phonon Raman spectroscopy. The originality of the project is that epitaxial growth of molecular crystals can be tuned by variable substrates (as it is a standard approach for inorganic epitaxy). Moreover, one further central question for the appearance of substrate-induced crystal structures is addressed: the role of the crystallisation kinetics will be separated from the influence of the substrate geometry for polymorph formation.
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Spectroscopy and Microscopy 15:40 - 16:10 | |
Femtosecond Photoexcitation Dynamics of Atoms and Molecules inside Helium Nanodroplets Abstract: Superfluid helium nanodroplets (HeN) represent a promising approach to study femtosecond dynamics in previously inaccessible systems. Here, the first time-resolved investigations of single indium (In) atoms and In2 molecules located inside HeN are presented, which were obtained by combining time-resolved photoelectron and photo-ion spectroscopy and time-dependent helium density functional theory modelling.
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In situ temperature control in Raman microscopy – Hot or Not? Abstract: In the last year, students had the following task at our advanced lab exercise:
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Precise measurements of potassium ions with Fourier transform spectroscopy Abstract: Spectroscopic experiments have been utilized for investigating chemical and physical phenomena. In particular, Fourier transform spectroscopy (FTS) has been the leading spectroscopic tool in molecular spectroscopy. FTS has allowed for the precise measurements with both high resolution and broad spectral range. These advantages revealed the vibrational wavepacket motion in Na$_2^+$ with FTS. Dual-comb spectroscopy (DCS) as a special subspecies of FTS offers utmost spectral resolution by overlapping two slightly detuned frequency combs, however so far mainly limited to linear absorption spectroscopy, caused by the comparably low intensity of the combs.
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Differential Phase Contrast Imaging in Scanning Transmisson Electron Microscopy Abstract: Differential phase contrast in scanning transmission electron microscopy (DPC - STEM) measures small displacements of an electron beam with a position sensitive detector due to the presence of electromagnetic fields. Recent improvements of the technique in combination with aberration corrected microscopes now allow imaging electro-magnetic fields down to atomic scale resolution. Integration of DPC signals enables the possibility to detect light elements, such as hydrogen, nitrogen or oxygen, next to heavier atom columns which is a major advantage compared to other high-resolution STEM imaging techniques. To demonstrate the power of this technique, two examples of DPC measurements are shown on this poster. First the magnetic domain structure of a thin, polycrystalline, Co-film and its evolution upon tilting within an external magnetic field is shown. Second, a comparison of high-resolution HAADF and iDPC images of GaN are shown and demonstrate the benefits of this new STEM imaging method. Combined with image simulations based on multislice algorithms we are now able to fully explore all the new possibilities given by (i)DPC STEM imaging.
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Ultrafast control of helicity dependent electron dynamics in molecules and solids Abstract: To study ultra-fast charge carrier dynamics in chiral molecules and ferromagnets in real time we develop a gas-filled hollow-core-fiber compressor to compress the 25-femtosecond near infrared laser pulses from commercial laser system. The resulting near single-optical-cycle transients will be converted to circular polarization by an all-reflective octave spanning phase retarder that overcomes the bandwidth and pulse duration limitations of conventional wave plates. The envisaged electric field waveforms approach the single cycle limit in time domain and single revolution limit in the polarization plane. Equipped with this novel platform for ultrafast polarization sensitive experiments optical dichroism photo-electron spectroscopy of charge dynamics in chiral molecules and studies of magnetic circular dichroism under the influence of strong electric pumping will be pursued.
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Physics Doctoral School 16:10 - 17:30 | |
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Conceptual studies for a future collider beam dumping system Abstract: The Future Circular Collider project [1] investigates future options for particle accelerators. One such options, which is also strongly encouraged by the European Strategy for Particle Physics, is a 100 km circumference lepton collider (FCC-ee). This collider will function as a Higgs-Factory and therefore is supposed to have high intensity/high energy density particle beams [2].
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Strongly correlated quantum transport systems in non-equilibrium Abstract: Strongly correlated materials are a promising class of materials, that could help in the advancement in various technological areas. For using strongly correlated materials in these areas a fundamental understanding of these systems in non-equilibrium is of major importance. Strong correlations cannot be properly taken into account by DFT calculations. While other methods are able to take these correlations into account, these methods are based on simple model Hamiltonians. Our goal is to combine the advances of ab-initio methods like DFT and methods suited for correctly describing strong correlations. We aim for a combination of a DFT+NEGF approach and methods well-suited for strong correlations allowing not just qualitative but also quantitative predictions of the behavior of strongly correlated materials in non-equilibrium. Using this combination we aim to not only describe results of past experiments but to also predict results of future experiments. Using this combination we are going to learn more about the properties of these materials and their suitability for various technological applications.
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Structural transitions of organic polymorphs on metal surfaces Abstract: Organic molecules can arrange in various polymorphs on surfaces, which can be already determined with an in-house program named SAMPLE[1]. Knowing the corresponding physical properties of the polymorphs allows to computationally design novel materials with superior properties. However, to be able to suggest a route on how to realize these materials, also knowledge about how the different polymorphs transform into each other is required. In particular, the following questions have to be answered beforehand: How stable single polymorphs are under specific conditions? Under which mechanisms phase transitions occur? Is there a sequence of process parameters that allows to kinetically stabilize a specific target polymorph? The key to answer these questions is to estimate lifetimes and transitions rates of polymorphs as function of environmental conditions. In practice, the main ingredients for the lifetime determination are the electronic energy barriers between neighboring polymorphs, which demands exploring the multidimensional potential energy surface. The harmonic approximation, Nudged Elastic Band method and the Dimer Method are tools, which enable a more or less sophisticated computation of energy barriers.
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Non-destructive analytical determination of coated wood, paper and composite surfaces by combining AFM with spectroscopic methods Abstract: The aim of this PhD thesis is the development of a non-destructive
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Long-Range Correlations and Magnetic Ordering in Pyrochlore-Iridates Abstract: In this thesis, we will investigate the electronic, magnetic, as well as topological properties of Pyrochlore Iridates. These materials are under intense investigation right now, since they are meant to host non-trivial topological states. However, previous theoretical studies did not yet converge on a consistent picture for the physical properties. Therefore, we will use state-of-the-art numerical techniques to clarify some of the open questions. We will
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Effects of phonons in strongly correlated systems out of equilibrium: application to Mott photovoltaics Abstract: Theoretical comprehension and simulation of strongly correlated systems driven out of equilibrium is a major challenge in current research. The role of phonons in such situations is still under debate [1]. Its understanding is important for possible applications as photovoltaics and RAM memories [2][3]. The aim of our study is to address the influence of these lattice vibrations on the electronic motion. We include electron-phonon interaction in a perturbative scheme, to be embedded in a successful computational scheme for the treatment of nonequilibrium systems with strong electron-electron interaction [4][5]. We consider a strongly-correlated layer between two metallic leads, under the influence of a time-periodic electric field [6]. The Floquet nonequilibrium steady-state reached in this setup will offer insights to understand the interplay between electronic correlation and eletron-phonon interaction.
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Transition Metal Chalcogenides under Extreme Pressures: Material Properties from First-Principles Calculations Abstract: Transition metal chalcogenides (TMC, C = S, Se, Te, Po) tend to crystallize into layered structures [1] that can exhibit interesting phenomena such as charge-density wave (CDW) formation or superconductivity (SC). While transition metal dichalcogenides (TMC$_2$) and their behaviour as a function of pressure have attracted great research interest in recent years due to the interplay of CDW and SC in metallic phases on the one hand, and photovoltaic prospects in semiconducting phases [2,3,4] on the other hand, complete phase diagrams with respect to pressure for the full TM$_x$C$_y$ systems are largely unexplored.
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Understanding heat transport in metal-organic frameworks in real and reciprocal space Abstract: Metal-organic frameworks (MOFs) are a type of highly porous materials consisting of inorganic nodes connected by organic linkers, which have been thoroughly investigated in the past two decades. They show promising applications regarding gas storage, gas separation and catalysis. Many of the processes occurring in applications of MOFs rely on the dissipation of heat. Therefore, it is crucial to investigate heat transport properties in these materials. Due to the sheer number of possible materials, it is not sufficient to just investigate the thermal conductivity for individual MOFs, but a fundamental understanding regarding the heat transport mechanisms in these materials is desired.
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High-temperature superconductivity in SuperHydrides at extreme pressures Abstract: The over 100 years old challenge of finding a room-temperature superconductor might be close to an end. The discovery of a Tc of 203 K in sulfur hydride at 150 GPa (2014), and 260 K in LaH10 at 130 GPa (2018) has re-ignited interest in superconductors, which has kept growing during the last six years [1]. Thanks to their high-energy unscreened ionic vibrations, hydrogen-rich materials (superhydrides) are in fact optimal candidates for phonon-mediated high-temperature superconductivity, and lanthanum hydride currently holds the record for the highest critical temperature ever recorded in experiments. In our work we use genetic algorithms for crystal structure prediction to identify new superhydrides, and determine their electronic and superconducting properties using Density Functional Theory (DFT) and its extensions. We aim at exploiting the exceptional properties of superhydrides to overcome the limit of room-temperature superconductivity, and reduce the extreme pressures that are necessary to stabilize currently known superhydrides. Using first-principles computational methods, we unveiled the role of hydrogen in superconductivity of high-Tc yttrium hydride clathrates [2] and calcium boron hydrides [3].
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Ultrafast Charge and Spin Control in Nanoengineered Devices Abstract: Ultrafast light-field control of spin dynamics and magnetic moments paves the way for future coherent spintronic applications, spin transistors and data storage by establishing optical frequencies as the speed limit. Although the ultrafast manipulation of spins is restricted by the weak coupling between light and spin, a recent experimental and theoretical study [1] demonstrated the light-wave control of magnetic moments on a sub-fs time scale. Based on this work we set up an experimental program dedicated to the investigation of magnetization dynamics with attosecond temporal and nanometer spatial resolution. Photoelectrons, thereby, are one of the most promising candidates as experimental observable as they can provide both - spatial and temporal - information. In particular, the unique combination of our NanoESCA photoemission electron microscope and our ultrafast laser systems carries unprecedented potential for the exploration of magnetization dynamics in alloys and magnetic multi-layer structures. Preliminary experiments already show the feasibility of imaging magnetic domain textures from a buried interface by employing circularly-polarized visible light pulses and utilizing magnetic circular dichroism near the Fermi level. Furthermore, first time-resolved measurements reveal a significantly intensity dependent response to an infrared pump-pulse inducing either a dynamic demagnetization process or the formation of a new domain network.
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Orbital Mapping by STEM-EELS Abstract: The shape of electron orbitals influences properties on the atomic, as well on the macroscopic scale. Despite their importance, however, there are only very limited possibilities of directly investigating individual orbitals inside a specimen so far. While orbital mapping with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) was found to be possible [1], two major challenges related to the inherently poor signal-to-noise ratio (SNR) and the required low symmetry of the samples prevented more routine studies.
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Cylindrical gas-gap capacitor structure: Performance and reliability of gas-gaps within semiconductor devices Abstract: The aim of this thesis is to obtain a physical model for gas gaps within micro- and nanometer silicon structures at high electric fields. The fundamental approach of this study is key to enable a profound assessment of such systems and their evolution in terms of performance and reliability. Theoretically, the Paschen law describes the electrical breakdown of a gas between two electrodes as a function of gas pressure and gap distance. For gap distances smaller than the mean free path of the electrons it predicts an increase in breakdown voltage. However, in systems where pressure and gap distances are decreased to extreme values electrical breakdown of the gas via the underlying Townsend mechanism is unlikely. In this regime, we expect to have a significant rise of the leakage current due to field emission such that electrical breakdown will be a matter of definition related to the amount of leakage. The influence due to geometry and surface effects might introduce a non-negligible impact. Additionally, new current mechanisms are conceivable via residual gas within the gap such as ion induced effects or surface interactions.
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Late Posters | |
Highly Integrated Ion-Traps for Quantum Computing Abstract: While not a new concept anymore, quantum computing is currently being pushed by numerous global players to speed up several currently intractable computer calculations, most notably in quantum chemistry and data security. Trapped-ion quantum bits (qubits) are, among others, a promising candidate for future quantum computers. These use the quantized energy levels of the valence electron to encode quantum information. A future quantum computer will require thousands of physical qubits to function correctly. As part of the PIEDMONS (https://www.piedmons.eu) project, we address two obstacles that currently prevent scaling-up the trapped-ion platform. Like most quantum computers, trapped ions require cryogenic temperatures to keep their quantum state. However, increasing the trap size to accommodate that many qubits will lead to significant heat dissipation due to wire resistance and dielectric losses. Thus, Alexander will characterize the oxide in the operating-frequency range (about 30MHz) and improve its quality to reduce dielectric losses. Secondly, he will investigate breakdown mechanisms between electrodes. The final target is an improved trap design that tolerates higher voltages and offers reduced losses and higher ion density.
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