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. Thirty-three institutes from six faculties are presently involved.
Advanced Materials Day is the yearly meeting where the members of the FOE present their latest results. In 2019, the meeting will be held on September 26 at the Neue Technik campus in HS H "Ulrich Santner" in the Chemistry building.
Talks | |
| 09:00 - 09:10 |
Introduction |
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09:10 - 09:30 |
Real-time tracking of electron and spin dynamics Abstract: By means of attosecond spectroscopy we can explore electron and spin dynamics in real time. This information can be crucial to understand the microscopic origin of a functional material’s interaction with light. As examples I will show how quickly silicon can absorb a photon and introduce an experiment that recorded the fastest magnetic switching ever achieved.
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 09:30 - 09:50 |
Porous Materials@Work Abstract: The lead project „Porous Materials @ Work” aims at establishing a technology platform within the Graz University of Technology’s research portfolio by connecting existing skills and by developing expertise in nano-, meso- and macroporous materials as an exciting state of matter. Porous Materials @ Work aims at excellence in science, research, and training to create a beacon that attracts scientists and industry alike to work with TU Graz faculty and to draw from their considerable expertise.
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| 09:50 - 10:10 |
Design of sustainable hybrid electrochemical capacitors Abstract: Hybrid electrochemical capacitors display higher power than batteries and higher energy than electrical double-layer capacitors (EDLCs). Generally, in these devices, high surface area activated carbon is used as electrode materials. To enhance energy, we have implemented redox active aqueous electrolyte which transforms the charging mechanism of positive electrode to a battery-like, and it is then internally hybridized with an electrical double-layer (EDL) negative electrode. Thereby, a hybrid cell displays twice higher capacitance than its symmetric counterpart. This construction is advantageous owing to the low assembling cost, no toxicity issues and high cycling performance. The presentation will include data related with investigation of carbon/redox specie interface by thermogravimetry coupled with mass spectrometry (TG-MS) and Raman spectroscopy.
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10:10 - 10:30 |
Studies of ionizing radiation effects in nanoscale CMOS technology nodes Abstract: X-ray radiation damage of semiconductor devices originates from radiation-induced fixed charge in the insulating regions and interface traps [1]. Device arrays fabricated in 28 nm bulk CMOS with pMOSFET and nMOSFET transistors of different dimensions have been studied. Stress tests have been performed with X-rays of energies in range 10 to 40 keV. Transfer and output characteristics have been measured before irradiation as well as after 12 steps of total ionizing dose (TID) to track evolution of device parameters. These steps start with 100 krad and 500 krad, corresponding to TID levels close to those experienced by instruments in space missions or medical imaging and reach ultrahigh levels of 900 Mrad, which is of interest for high energy physics experiments. Similarly to older technology nodes the effect of radiation induced narrow channel effect (RINCE) [2] related to traps within the shallow trench isolation (STI) is observed on device characteristics. Transistors in the 28 nm process, in contrast to technology nodes down to 65 nm already widely studied for TID effects, are equipped with high-K/metal gate. Therefore material properties and formation of traps might have to be reconsidered when interpreting the post-irradiation measurement results. TCAD device model including HfO2 - SiO2 gate stack and strained channel is adapted to measurement results. In this talk the 28nm CMOS process will be introduced and selected device parameters will be analysed with respect to radiation damage. Finally the approach of employing the model to examine various radiation damage effects observed after TID stress will be discussed.
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| 10:30 - 11:00 |
Coffee Break |
| 11:00 - 11:20 |
Silica-based nanostructured particles/ SOMAPP Lab Abstract: Lipid based liquid crystalline systems form various structures depending on the lipid composition, their hydrophilic head group as well as their lipophilic tail. These self-assembled structures formed are affected by temperature and additives[1–4]. Additionally, they can also be dispersed to form nanostructured particles.
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| 11:20 - 11:40 |
Investigating the Mechanisms of Dolomite Formation at Low Temperatures Abstract: Dolomite is a Ca-Mg-carbonate mineral that is abundant in ancient carbonate platforms and is an important component of petroleum reservoir rocks. In its ideal state dolomite has the stoichiometric composition CaMg(CO3)2 (i.e. molar Ca:Mg = 1:1) and consists of an ordered arrangement of alternating layers of Ca2+ and Mg2+ cations interspersed with CO32- anion layers normal to the c-axis. The formation conditions of dolomite are not clearly understood as so far dolomite synthesis from an aqueous fluid under laboratory conditions and at ambient temperatures has not been established. Recent synthesis experiments at >140°C indicate that dolomite forms through a series of intermediate phases starting with an amorphous calcium magnesium carbonate (ACMC) precursor being replaced by very high Mg-calcite (VHMC). The VHMC products are subsequently replaced by a stoichiometric dolomite. However, a large gap of knowledge exists with respect to this reaction pathway at low temperature.
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11:40 - 12:00 |
The Paper Pulp Fiber to Fiber Interface Abstract: The bonding formed by two single cellulosic fibers and the corresponding Fiber to Fiber interface is a key feature of paper-based materials. They play a critical role on its response to strain and relative humidity changes. Although several experiments have been performed during last years this interface is still far form being clearly understood. In this talk we will first present a general overview of the research activities at TU-Graz on paper. Then, we will present previous experimental studies on the Fiber to Fiber interface. Finally, we will present our approach using Ptychographic X-ray Computed Tomography. Ptychography is a phase-contrast imaging technique capable of retrieving 3D images with nano-metric resolution.
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Posters 15:30 - 17:30 | |
Comparing new testing methods for the sulfate resistance of shotcrete Abstract: Modern excavation and tunnelling methods rely on the application of mechanical stabilisers such as shotcrete. Shotcrete frequently encounters chemically aggressive solutions, leading to, amongst others, external sulfate attack. A better understanding of the mechanisms of this type of attack is necessary to better assess the durability of newly developed shotcrete mixes. We compare the performances of 7 dry-mix shotcrete mix designs (using different amounts and types of supplementary cementitious materials) in novel sulfate resistance tests using either powdered samples or drill cores. The chemical and mechanical changes of the sample materials are monitored during the tests, showing the main chemical changes to be the dissolution of hydrated cement phases and the neo-formation of ettringite and calcite. The precipitation of ettringite in turn is responsible for destructive expansion, causing cracks and breaking. We find that certain mix designs perform better than others, forming less ettringite and in turn showing lower expansion. These differences are presumably due to variations in the mix designs such as supplementary cementitious materials used and water/binder ratios.
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Finding and Understanding Surface Structures with SAMPLE Abstract: Even if the physical properties of an organic semiconductor are ever so promising in the bulk phase, they may drastically change upon adsorption on the surface. Specifically, surfaces can induce the formation of polymorphs with worse, or under the right conditions, also greatly improved properties. Normally, the exponential growth of possible polymorphs with system size prohibits rigorous computational studies, that could explore the full configurational and thermodynamic search space. Thus, we use SAMPLE [1,2], which employs machine learning to suitably fit a physical energy model and therewith efficiently calculate the adsorption energies of an exhaustive set of coarse grained polymorphs.
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Investigation of welding parameters on geometric evolution in Wire Arc Additive Manufacturing via Cold Metal Transfer Abstract: Wire Arc Additive Manufacturing (WAAM) is an interesting alternative to the well-known and wide spread AM techniques and a powerful technique to build-up bigger near net structures by higher deposition rates. The investigated CMT based WAAM process of the AM structures takes place layer by layer and each stacked layer consist of multiple weld tracks arranged next to each other. In order to meet the geometric requirements of the final AM structure, a comprehensive knowledge of the correlation between welding parameters and the geometric evolution of the weld bead, overlapping distance as well as average growth rate per layer is needed. A range of suitable parameter configurations and its correlation to weld bead geometry were identified and for selected parameter sets overlapping welds with varying axial offset were produced. To measure the geometric evolution and to evaluate a proper offset, a digital microscope was conducted and analyzed. Considering the gained results, for two selected parameter sets 3D AM-structures with pre-defined dimensions were build-up. By applying the increased energy input parameter set, less layers were required to build-up the 3D part, than for the low energy input parameter set.
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Development of a process flow to enable packaging on wafer level Abstract: In an effort to enhance packaging efficiency (e.g. throughput, effort…) the currently used serial processing steps are aimed to be transferred into parallelized process steps. Based on this motivation, the development of a process flow enabling packaging on wafer level is comprised in this work. The introduction of an electrically insulating glass-substrate as a packaging material requires the adaption and integration of various established unit-processes in combination with the implementation of novel process steps. Apart from demonstrating the product-line fabrication feasibility of such a package, the characterization of device specific electrical parameters as well as diverse metal/metal and metal/glass – interfaces are the focus of this work.
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Coupling of Dislocations and Point Defects in Continuum Mechanics 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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Impact of Powder Production Process and Powder Properties on Selective Laser Melting of Ti6Al4V Abstract: Besides process parameters powder properties such as grain size, form and chemical composition have the highest impact on material properties of parts produced by selective laser melting. In scope of this work this influence for differently produced Ti6Al4V powders from 3 different providers on density and mechanical properties of build samples has been investigated.
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Dual Comb Spectroscopy Abstract: Dual Comb Spectroscopy combines high spectral resolution (relative resolution demonstrated up to 10$^-$$^1$$^1$) with broad spectral coverage (>> 10 THz) and short measurement times (down to microseconds). In the recent years, the young spectroscopic method has proven its capabilities in spectroscopy in different spectral regions ranging from the visible across the infrared spectral region into the THz domain. Our recent efforts aim at the extension of the young spectroscopic method towards novel applications in the so far underexplored extreme ultraviolet region, but also towards imaging modalities via Raman spectroscopy and optical coherence tomography.
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Preliminary study on the AddJoining process over additively-manufactured metallic parts Abstract: The production of a polymer-metal hybrid components completely by additive manufacturing processes would allow great freedom in respect to part geometry, without the need to resort to conventional machining steps. Joining steps could be skipped as well if the polymeric features of such a component were directly assembled over the metallic parts, however rough raw metallic AM surfaces may be. Saving machining and joining times would lead to faster production rates, which is generally of great interest. The present study represents a preliminary attempt to produce polymer-metal hybrid coupons solely by additive manufacturing, avoiding machining and joining steps.
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Why are charge carrier mobilities in organic semiconductors typically low? Are COFs and MOFs the solution? Abstract: A crucial factor determining charge transport in organic semiconductors is the electronic coupling between the molecular constituents, which is heavily influenced by the relative arrangement of the molecules. To systematically investigate this interplay between transport relevant parameters, energetic stability, and the crystal structure we performed first principles calculations for the instructive example of quinacridone. For this material one finds three polymorphs with fundamentally different packing motifs. Additionally, based on the α-polymorph, an artificial coplanar quinacridone crystal can be constructed. The latter allows correlating electronic properties like transfer integrals t and band-widths with the total energy of the crystal. This way we identify the combination of Pauli repulsion and orbital rehybridization as driving force steering the system towards a structure in which the electronic coupling is minimal, resulting in poor transport properties. The general nature of these observations is supported by equivalent trends for an analogous pentacene model system. Thus, one can conclude that the electronic interaction between neighboring molecules provides a driving force towards structures with low transfer integrals and bandwidths, resulting in reduced transport properties. This also means that the design of high-performance materials cannot rely on the “natural” assembly of the pi-conjugated cores of the semiconducting materials into their most stable configurations. Rather, it must include the incorporation of functional groups that steer crystal packing towards more favorable structures. Freezing certain degrees of freedom by
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Electron Microscopy as an Essential Tool in Electrochemistry: Assessing the Surface Morphology of Al - Electrodes Abstract: The aim of this work is to realize a secondary aluminum battery, using metallic aluminum electrodes in combination with a deep eutectic solvent consisting of AlCl3 and urea as electrolyte [1, 2, 3].
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Integrated contactless temperature-control for Electron Beam Additive Manufacturing Abstract: Additive manufacturing is an upcoming and novel technique to meet industry’s requirement of producing near-net shape parts providing full functionality. Special focus is paid in processing titanium alloys, e.g. Ti-6Al-4V, which, due to its excellent relative strength, is widely applied in aerospace industries. In order to guarantee a stable and reproducible production process, an accurate and reliable temperature control of the additive manufactured structures is of interest. Due to its layer-by-layer build-up, conventional contact temperature measurement by means of thermocouples is not suitable and contactless temperature measurement is preferred. The prevailing vacuum atmosphere combined with the extensive heat input of the electron beam result in an evaporation of aluminium during processing Ti-6Al-4V and interfere contactless measurements. In order to get rid of certain influences, and to prevent coating of the pyrometer optics, a protection device providing heat resistant foil transport was designed and implemented. For the 1-color radiation pyrometer an emissivity for the overall system was determined by the means of a benchmark test and comparing the deviation between temperature curves recorded by thermocouples and pyrometer. Furthermore, the system was mounted on the wire feed unit in order to determine the temperature distribution during electron beam additive manufacturing and temperature curves for selected distances to the electron beam centre were recorded. The measured thermal cycles were analyzed and evaluated with respect to the prevailing peak temperatures, and the temperature distribution by reconstruction the resulting isotherms.
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Auxiliary master equation approach to the pseudogap Anderson model out of equilibrium Abstract: The auxiliary master equation approach [1,2] allows us to assess the time evolution and, in particular, the steady state properties of quantum impurities and small molecules in as well as out of equilibrium. It is based on a mapping of the physical system to an auxiliary open quantum system, whose dynamics is determined by a Lindblad master equation that we solve with Matrix Product States techniques.
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Adsorption and desorption of L-cysteine on nanoporous gold monitored by in-situ resistometry Abstract: Surface modifications of nanoporous metals have become a highly attractive research field as they exhibit great potential for various applications, especially in biotechnology. Using self-assembled monolayers is one of the most promising approaches to modify a gold surface, however, only few techniques are capable of characterizing the formation of these monolayers on porous substrates.
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Thermodynamic Precipitation Kinetic Simulation and Creep Deformation Modelling of Martensitic Steel X20 Based on Microstructural Evolution Abstract: Every material is subject to change over a certain period of time. Chemical composition and physical properties alter, and the material performance deteriorates. Lifetime and behaviour of a material strongly depend on influences affecting it, especially temperature and pressure. Over the years, great efforts have been made to predict material behaviour and to develop new, improved materials with better creep resistance and service properties.
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Database Development for Thermodynamic Simulation of Ta-based Z-Phase Formation in Martensitic Z-Steels Abstract: To raise efficiency of thermal power plants and to reduce CO2 emissions, creep-resistant materials suitable for higher operation temperatures and pressures are needed. One materials group fulfilling the demands of reaching at least 600°C and 300 bar (without being too expensive for the energy sector) are 9-12% martensitic Cr-steels. Z-steels represent a new promising generation of 12% Cr steels which contain Tantalum. High Cr content and Ta addition cause a very fast transformation of carbo-nitride precursor phases MX and M2X into long-term stable and finely distributed Z-phase CrTaN. This CrTaN Z-phase (in contrast to its harmful relative CrVN) provides significant precipitation strengthening during creep conditions.
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Describing complex intermolecular interactions with SAMPLE: Pushing the feature vector to the limit Abstract: The SAMPLE [1,2] approach for structure search on surfaces enables predictions of the geometric structures of inorganic/organic interfaces and their intermolecular interactions with uncertainties close to that of the underlying DFT calculations. However, so far the method has only been tested for simple, highly symmetric adsorbates with trivial chemistry. There, the interactions were overwhelmingly determined by either van-der-Waals interactions [1] or electrostatic interactions [2,3].
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Energy filtered photoemission electron microscopy (EF-PEEM) of nanoparticles, nanostructures and surfaces Abstract: Photoemission electron microscopy (PEEM) provides a powerful and versatile method for the investigation of a large variety of materials and a characterization of their properties. At the Institute of Experimental Physics we use a NanoESCA photoemission electron microscope (from Scienta Omicron/Focus), equipped with a double hemispherical detector for energy filtering (EF) of photoelectrons. The instrument allows for micro-spectroscopy by analyzing the photoelectron spectrum integrated over a small selected area as well as spectro-microscopy by recording images for a selected kinetic energy of the photoelectrons with a resolution down to 30 nm. This enables, for example, the analysis of the chemical composition of a sample based on local work function variations or shifts of core-level states. The EF-PEEM can also be used for momentum-space microscopy, allowing for a mapping of the band structure of single-crystalline samples. The employed light sources range from a cw discharge lamp, providing 21 eV photon energy, to different available laser systems with a photon energy of a few eV. In particular, the combination of our femtosecond laser system with the NanoESCA is our prime interest, which enables the study of dynamic processes in the materials under investigation in the femtosecond time domain.
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Characterization and functionalization of boron nitride nanosheets with organo silanes. Abstract: Different fillers are used in order to improve the thermal conductivity of polymers. Boron nitride nanosheets are an ideal candidate for this kind of application, due to their appealing properties. These nanosheets have a band gap of 5.955 eV [1], which makes this material an electrical insulator, but with a very high thermal conductivity. However, one of the challenges of using these as fillers is their dispersion in the polymer matrix, because of the high tendency of the nanosheets to aggregate. In order to improve this, the idea was to functionalize the boron nitride nanosheets with organo silanes, so that the modified nanosheets can bond covalently to the polymer matrix, leading to the prevention of aggregation and an increased thermal conductivity of the polymer. Silanes such as (3-aminopropyl)dimethylmethoxysilane as shown in Figure 1, as well as (3-aminopropyl)trimethoxysilane and (3-aminopropyl)diethoxymethylsilane were used to functionalize the boron nitride nanosheets. The modified nanosheets were characterized by dynamic light scattering (DLS), small angle x-ray scattering (SAXS), infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-VIS), and atomic force microscopy (AFM).
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Hot torsion tests of 100Cr6 steel to simulate the cross-roll piercing process Abstract: In these days the steel 100Cr6 is the most commonly used steel when it comes to bearing steel applications. One established process route for bearing ring production is by machining of seamless steel tubes. Seamless steel tubes made of 100Cr6 steel can be manufactured by applying the process of cross-roll piercing. To ensure high quality tubes it is essential to know the deformation behaviour of the material to be processed. The present thesis approaches the deformation behaviour of 100Cr6 steel through simulating the cross-roll piercing process at different temperatures and strain rates by conducting hot torsion tests with a Gleeble 3800 as well as flow stress curve computations with the software JMatPro. The resulting experimental and modelled flow stress curves are compared to each other and to similar works from the literature. Choosing a specific 100Cr6 alloy for the hot torsion tests is also carried out on the basis of the JMatPro computations previously performed. Additionally, the hot torsion samples are evaluated in terms of PA grain size to gather information about DRX occurrence. It can be concluded that DRX occurred under all deformation conditions and that DRX grain size decreases with decreasing deformation temperature and increasing strain rate.
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Friction Riveting – Single-phase process variant Abstract: Friction Riveting can be used to produce multi-material metallic-insert dissimilar connections. In general, the process aims to be used as an alternative connection method, reducing the usage of mechanical fasteners and adhesives. In single-phase friction riveting a simpler approach is used to join the materials in comparison to the more conventional multi-phase process. A basic application of the process consists of joining a featureless cylindrical metallic cylindrical rivet to a non-reinforced polymeric plate. The single-phase variant does not make use of a higher load phase – i.e. a forging phase – designed to promote extra plastic deformation of the metallic rivet. As such, it can constitute a solution to applications where the normal load applied to the materials must be kept at lower values. In the same manner as the multi-phase friction riveting, this process can be applied to join non-reinforced and reinforced thermoplastics and thermosets. These having been successfully joined with metals such as aluminum, steel and titanium. This work demonstrates that is possible to join AA2024 rivets, with 5 mm of diameter, to non-reinforced polyetherimide plates. A Box-Behnken design-of-experiments and statistical analysis were used to set the parameter matrix and understand the correlations between the process parameters used and the resulting joint properties. The parameters used resulted in a large variation of mechanical energy input (151 – 529 J). Higher-energy joining conditions led to rivet over-deformation and material rupture. Lower energy input corresponded to the best performing joints, characterized by a bell-shaped rivet plastic deformation. Joints performed achieved a maximum ultimate tensile force of 7486 N. The results allow for single-phase friction riveting to be established as an alternative joining process.
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Improvement of hydrogen induced stress corrosion cracking resistance of ultra-high strength steel screws and fasteners Abstract: Among different forms of environmentally assisted cracking (EAC), hydrogen embrittlement (HE), or more specifically, hydrogen induced stress corrosion cracking (HISCC) is the most critical form while dealing with high strength steel used for manufacturing of screws and fasteners(1). The downsizing trend of steel structures for mobility applications to increase efficiency and decrease CO2 emission face this problem, as it is well known that increasing steel strength also increase its susceptibility to HISCC. Thus screw strength class 10.9 (900 yield and 1000 MPa tensile strength) are specified as maximum for safety-related HISCC resistance(2). The main project goal is to establish a controllable method for HISCC testing, which should lead to a better understanding of the embrittlement mechanisms and to evaluate different microstructures, which are tempered martensite, bainite and pearlite by applying different heat treatments to achieve tensile strength of 1400 MPa or higher. The HISCC testing procedure will be performed as Incremental Step Load Test (ISLT) according to standard ASTM F 1624(3) with in situ hydrogen charging by cathodic polarization and corrosion measurements.
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Raman microscopy of inorganic materials – A stone is a stone! Is a stone? Abstract: “In our current laboratory exercise research project we are investigating the composition of common inorganic materials (such as rocks, dirt, crystals, and building materials) and the microscopic imaging of their components. A selection of samples from interested hobby geologist will be available, but students are also encouraged to bring their own samples (anything you are interested in from the soil in your back yard, to a weird looking rock you found while hiking). Our goal is to demonstrate that even in the limited time available during a lab exercise it is possible to produce a good quality analysis of a complex real world sample.”
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The Influence of Substrate Temperature during Focused electron beam induced deposition (FEBID) Abstract: As the needs for reliable 3D-printing at the nanoscale are rapidly increasing, proper techniques need to be developed to push their capabilities beyond current possibilities. In this context, Focused Electron Beam Induced Deposition (FEBID) is a very promising technique, as it enables mask-less, additive direct-write nano-fabrication of freestanding 3D nano-architectures. For highest precision and reliability, local precursor coverage is of highest importance, as it determines the incremental growth rates and by that predictability and reproducibility. Recently, it was found the local beam heating massively influences the local coverage due to reduced residence times, which explains previously observed stability problems for larger 3D structures[1]. Based on this motivation, we here turn around the situation and lower the substrate temperature to study the implications on stability and precision.
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Feature Selection for Functional Properties: Predicting Surface Rearrangements Abstract: With this poster I present an overview over my planned dissertation project. I layout the stages and milestones and give a brief insight into the methods I will be using.
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PEDOT:PSS/CeO2 composites with enhanced electrochemical properties via inkjet printing for smart biointerfaces Abstract: Nanoceria is a prospect material for many bioapplications. Presence of both Ce$^{4+}$ and Ce$^{3+}$ in its compositions allow active ROS scavenging and antioxidant capabilities. Presented work demonstrates fabrication and electrochemical characterisation of thin film PEDOT:PSS/CeO$_2$ composites. For film deposition inkjet printing was used as fast and simple way to produce thin films and functional microstructures. Cyclic voltammograms of individual films and composite shows significant enhancement of electrochemical properties.
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Strong field and time resolved photoexcitation effects in Helium nanodroplets Abstract: Measurement of ultrafast photoexcitation dynamics of isolated indium (In) atoms inside superfluid helium nanodroplets (HeN) has recently proven the feasibility of HeN as cold containers for femtosecond time resolved spectroscopy. As next step towards more complex systems, photoexcitation dynamics of indium dimers (In2) were studied with femtosecond time-resolved photoelectron and photoion spectroscopy. To get further insight into how the electron emerges the droplet and interacts with the superfluid Helium environment after photoionization, laser-assisted electron scattering (LAES) as ionization mechanism of doped droplets is demonstrated. First measurements of quasi free electrons interacting with He / dopant atoms and the electromagnetic field of the femtosecond laser light are presented.
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Smart-Data Machine Learning for Surface Polymorph Prediction Abstract: In this contribution we introduce the SAMPLE approach[1,2], a structure search tool for commensurate organic monolayers on inorganic substrates. The major challenge hereby is the large number of possible polymorphs such monolayers can form. To overcome this challenge, SAMPLE employs physically motivated coarse-grained modeling in combination with Bayesian linear regression to efficiently explore the potential energy surface.
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Weight reduction of a component for a moon landing module through topology optimization and selection of a suitable alloy Abstract: The aim of this master thesis is to reduce the weight of a pressure regulator to a minimum, which provides helium from a reservoir to maintain the pressure in the fuel tank which supplies the thrust nozzles of moon-landing-module, while perfect functionality and safety is guaranteed.
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Vapour Deposition of Metal-Organic Nanoporous Materials Abstract: Metal organic frameworks are known for storage and release of gases, catalysis and molecular separation due to their intrinsic nanoporosity and high internal surface area. However, classical synthesis methods are not compatible with device integration or large area deposition, calling for a viable alternative. Therefore, my PhD project is concerned with the deposition of metal-organic nanoporous materials from the vapour phase leading to new fields of application.
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On- and Off-Switching of Ferromagnetism in Nanoporous Pd(Co) Abstract: In the present work the particular features of dealloyed, nanoporous (np) metals have been exploited to switch magnetism. Besides the pore and ligament morphology itself, residues of the initial alloy affect the overall properties of np metals. During the dealloying process, parts of the base alloy are buried under nobler alloy atoms inside the ligaments. Ultimately, this leads to a cluster distribution of the remnant base alloy inside the np network, which sensitively depends on the initial dealloying parameters [1,2].
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Simulating Charge Transport Through Metal-Organic Semiconductor Interfaces: Bulk or Contact Limited? Abstract: The performance of organic electronic devices crucially relies on an efficient charge injection. This efficiency is governed by a complex interplay of experimentally tunable properties like level alignment and disorder. The impact of this interplay on the bulk current is only poorly understood from a theoretical point of view. To overcome this lack of knowledge, we utilize mesoscopic simulations to predict the current density across the contact interface. In these simulations, charges are viewed to migrate through disordered organic semiconductors due to hopping between localised states. Parameters like injection barrier, energetic disorder, electric field, Coulomb interactions and temperature can be directly considered. This intuitive method holds the promise to understand the effects and interactions that govern the interplay between interfacial and bulk properties. We analyse the current density for instructive combinations of interface and bulk properties. This analysis yields two distinct regimes, a bulk limited regime and a contact limited regime. The evolution of the current density with respect to injection barrier, energetic disorder and electric field strength is investigated and the origin of bulk vs. contact limitation is analysed.
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Phase diagram of the extended Hubbard model including spin-orbit coupling on a honeycomb lattice Abstract: In 2004, by isolating single layers of graphite, the first 2D-Material Graphene was found by Geim and Novoselov. One year later, the existence of a quantum spin Hall (QSH) state was proposed for lattices of the honeycomb type, as realized in graphene, by including spin-orbit coupling. This was the starting point for
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On the unexpected behaviour of Ni-Au and Co-Au core-shell nanoparticles Abstract: We present molecular dynamics simulations, static basin hopping calculations as well as comparisons with transmission electron microscopy (TEM) studies of 5 nm Ni-Au and Co-Au core-shell particles upon heating. The bimetallic nanoparticles are monitored through a heating cycle up to 1300 K and their structural rearrangement is observed. Via static basin hopping calculations we show that decentralised cores represent for both model systems the energetically most stable configuration. Heating can trigger a rearrangement of an initially centralised cores, however, as temperature increases entropy becomes more dominant, which finally can result in an alloying of the cluster. We show that this fascinating behaviour is an interplay between atomistic and bulk characteristics deduced from surface size effects and bimetallic phase diagrams.
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Vanadium(V) oxide clusters synthesized by sublimation from bulk Abstract: We present a new approach to neutral vanadium oxide nanoparticles synthesized by sublimation from bulk in combination with a pickup by superfluid helium droplets. Time-of-Flight mass spectroscopy measurements clearly demonstrate the preservation of the bulk stoichiometric ratio of vanadium to oxygen in He-grown nanoparticles, indicating a tendency towards sublimation of two of more $V_2O_5$ complexes. This unexpected finding opens up new possibilities for a combined on-the-fly synthesis of nanoparticles consisting of metal and metal-oxide layers. In comparison to mass spectra obtained via direct ionization of vanadium oxide in an effusive beam, where strong fragmentation occurred, we observe a clear preference for $(V_2O_5)_n$ oligomers with even n inside the He nanodroplets, which is further investigated. Additional characterisation of transmission electron microscopy (TEM) studies were performed on these $(V_2O_5)$ clusters. Here the UV-vis spectroscopy and the TEM images were used to determine that the oxidation state of the clusters is preserved during the synthesis process.
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Three-dimensional geometric integrator for charged particle orbits in toroidal fusion devices Abstract: A three-dimensional integrator for guiding center orbits of charged particles in toroidal fusion devices with 3D field geometry is described. The integrator uses a representation of the electro- magnetic field by low order polynomials on a 3D tetrahedal grid and is intrinsically designed to preserve the total energy, perpendicular adiabatic invariant, and the phase space volume accu- rately for any grid size. Thus, it belongs to the class of geometric integrators.
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Simulation of AlGaAs oxidation in semiconductor devices Abstract: The wet oxidation process of AlGaAs has become of interest in the light of Vertical Cavity Surface Emitting Laser mass production, as the optical and electrical confinement provided by the oxide enables high power conversion efficiencies. The produced oxide, however, is reported to reduce its volume, which introduces high-stress fields and aids the growth of so-called dark-line defects. A lot of research can be found about simulating the oxidation and failure modes of VCSELs, but there is very little information on how dark line defects are generated. In this poster, we present the first steps of including the stress field caused by the oxide as a driving force for defect generation by using finite element simulations. We calibrated the oxidation using a reaction limited Deal-Grove model and used it in combination with linear elasticity, to show the possibility of nonlinear deformations around the oxide tip. This insight will aid the creation of a defect generation model and enable the design of more robust VCSELs.
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Integrated Cryo-Electronics for Trapped Ions Abstract: The PIEDMONS project addresses several ways to enhance the integration of ion trap quantum devices. One important possible improvement is the integration of digital-to-analog converters directly into the ion trap to replace complex analog connections by simpler digital ones.
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CP-FE modelling and experimental investigation of gradient structured Al wires Abstract: During past decades some novel severe plastic deformation (SPD) methods have been developed to strengthen materials by achieving fine and ultrafine-grained (UFG) structures. However, the processes did not succeed from industrial point of view due to small size of the products and the required number of passes to reach to a desirable level of enhanced properties. To achieve a combination of high strength and ductility, one can develop advanced structural materials by artchitecturing imperfection across different length-scales. Among different introduced strategies, the gradient structures in form of gradually changes of microstructural elements (grain size, twining thickness and dislocation density) is shown to lead to an extraordinary strength-ductility synergy. Multiscale modeling plus crystal plasticity theory can be used to simulate microstructural evolution of complex deformation and strain inhomogeneity processes. In this study, we have developed gradient structured wires using ECATD method. To perform FE simulations, we have used NEPER to develop 3D polycrystalline geometry and DAMASK as a subroutine for ABAQUS. To evaluate the codes, We have performed FE simulations for pure torsion deformation and simple compression.
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Demand-based coupling of the scales: An application to the finite temperature CADD method | |
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Material Behavior Across Scales: Grain to Continuum Abstract: Granular materials are the second most manipulated material in industry, only after water. They span the wide spectrum ranging from assemblies of non-cohesive particles to consolidated solids formed of particulate precursors. Due to their discrete and heterogeneous nature, variety of microstructural features and grain-pair interaction mechanisms, as well as loading-induced anisotropic evolution of microstructure, these materials manifest interesting behavior traits. Developing an understanding of the macroscopic behavior of these materials as well as its connection to the micro-scale phenomena happening at grain-scale is, therefore, essential for analysis of existing materials as well as designing metamaterials.
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SimCP – Simulation-aided Cell Production – Investigation of the expansion of Li-ion cells with Si-based anodes Abstract: At the moment, Li-ion cells excel other battery technologies regarding capacity and energy density. They also show potential for further development. For a significant improvement of cell performance, the use of new electrode materials is necessary. Si and Si-compounds are promising candidates for anode materials due to their high capacity for the insertion of Li-ions. One big drawback, which hinders commercialization, is the large expansion of these materials when the ions are inserted. To overcome these problems, a detailed knowledge about the materials and their expansion behaviour under various conditions is necessary and vital for further development and optimization.
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Nanoporous Structure of Dealloyed Metals Analyzed by Electrochemical Impedance Spectroscopy and Positron Annihilation Lifetime Spectroscopy Abstract: Via electrochemical dealloying, a selective etching process [1], nanoporous gold (npAu), palladium (npPd) and platinum (npPt) was prepared from the initial alloys $Ag_{75}Au_{25}$, $Co_{75}Pd_{25}$ and $Cu_{75}Pt_{25}$ and characterized by electrochemical impedance spectroscopy (EIS) and positron lifetime spectroscopy (PALS). These dealloying systems exhibit clear differences in their impedance spectra which arise mainly from the characteristic length scales in the porous structures [2]. By fitting these spectra, structural parameters such as the pore radius, the ligament size, and the pore length can be determined. EIS also yields access to the tortuosity of the pores [3]. In all cases, the pore size is found to be about 50 % larger than the ligament size, which is in good accordance with literature [4]. Occluded pore shapes were estimated from the EIS spectra in the Nyquist plot representation for all investigated nanoporous metals. Particular focus is placed on structural changes due to heat induced coarsening of nanoporous gold. Beside an increase in the pore radius, also a change in the EIS spectrum and a decrease in the tortuosity, which are indications for more cylindrical pores, can be observed.
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4-D printing of NiTi Shape Memory Alloys Abstract: Nickel-Titanium (NiTi) shape memory alloys (SMA) have been broadly employed to biomedical and aerospace industry due to its functional properties, namely shape memory effect (SME) and superelasticity (SE). Usually, NiTi is thermo-mechanically processed from cast ingots, thereafter forming into rods, bars, sheets and wires. For this purpose, the material must follow a complex combination of working conditions. However, intrinsic problems such as high reactivity and strength configure an additional challenge to their processing. Moreover, if a complex design is aimed, the processing (and the shape memory behavior) might be compromised. Hence, the application potential of NiTi has been somehow limited.
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Towards new plasmonic materials: Synthesis of K and K-Au nanoparticles with helium droplets Abstract: We report on experiments on K and bimetallic K-Au nanoparticles produced under UHV conditions by synthesis in helium nanodroplets. Bimetallic K-Au nanoparticles are promising candidates as building blocks for future meta-materials due to their excellent plasmonic properties. Considering the growing importance of plasmonic technology with diverse applications, for example, in photovoltaics, medical diagnostics, catalysis and surface enhanced Raman spectroscopy, the search for better plasmonic materials constitutes an important task for both science and industry.
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Investigation of soft matter materials with the new system RISE combined with EDXS Abstract: At the Institute of Electron Microscopy and Nanoanalysis of Graz University of Technology (FELMI) together with the Graz Center for Electron Microscopy (ZFE) the new system RISE (Raman Imaging and Scanning Electron microscopy) offers the possibility of high resolution imaging by the scanning electron microscope Zeiss Sigma 300 VP (Oberkochen, Germany) and chemical analysis with the attached Raman microscope from WITec (Ulm, Germany). [1,2,3] Additionally the arrangement is equipped with a modern silicon drift detector from Oxford (UK) for energy dispersive x-ray spectroscopy (EDXS). This setup enables to distinguish different complex materials concerning layers, filler particles and additives and provides sample characterization in the same region of interest (ROI). This is realised in an uncomplicated manner by a stage movement (semi-automatically) between the SEM and the Raman measurement position in the specimen chamber. Different samples were investigated to present the possibilities of the new system.
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Alignment Study of Epitaxially Grown Cu(BDC)-MOFs via X-ray Pole Figure Technique Abstract: Aligned metal organic frameworks (MOFs) are interesting for usage in optical, sensor and microelectronic application.[1] Recent works demonstrated how MOFs can be epitaxially grown on a copper hydroxide surface.[2,3] In this work, copper-based MOFs linked in two dimensions by 1,4-benzenedioic acid (BDC) are grown on Cu(OH)2 nanobelts. The nanobelts, with dimensions of several µm in length, and approximately 20 nm in width, are deposited on silicon surfaces by solution processing. It is apparent that the alignment of the Cu(OH)2 nanobelt substrate is an important parameter for the controlled, oriented growth of the MOF. Samples are investigated using rotating grazing incidence X-ray diffraction (GIXD), probing a large volume of reciprocal space by rotation of the sample around its surface normal. This data then allows the determination of the nanobelt alignment by calculation of pole figures. Applying the same approach to the MOF, we studied the degree of alignment of the substrate transferred to the MOF. In a subsequent step, the crystal structure of the MOF can be compared to known crystal structures from literature.[4] Interestingly, we found that none of the known crystal structures is matching the experimental peak pattern, i.e. Cu-BDC can form a new crystal structure when grown on Cu(OH)2 nanobelts.
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Recovery and recrystallization study of an Al-3wt%Mg alloy using a unique combination of quantitative difference-dilatometry and electron backscatter diffraction Abstract: Special rolling and heating procedures, as well as the formation, migration and annihilation of dislocations are the cause for a well- defined microstructure, which results in the improvement of the properties of workhardenable metallic materials. Fundamental knowledge of these processes as well as the microstructure is also of utmost importance for the simulation of large- scale industrial processes, especially in aluminum industry.
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Studying surface dynamics and THz collective excitations in topological insulators with helium atom scattering Abstract: Inelastic helium atom scattering (HAS) is the ideal tool to study the surface vibrational modes of topological insulators such as $Bi_{2}Te_{3}$ and $Bi_{2}Se_{3}$, since it provides access to the low-energy meV region and allows to study subtle effects such as the influence of van der Waals bonding in layered crystals[1]. Considering that HAS has recently been recognised as a powerful tool to investigate the electron-phonon interaction at surfaces[2,3], the question arises whether it can also be used to study charge density waves (CDWs): Periodic modulations of the electron density, which are ubiquitous phenomena in crystalline metals[4].
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Development of site-specific arrays of pressure, temperature and humidity multi-responsive nanorods Abstract: Zinc oxide deposited by a novel new technique, Plasma Enhanced Atomic Layer Deposition (PEALD) is combined with a thermoresponsive hydrogel, namely p(NVCL), deposited by Initiated Chemical Vapor Deposition (iCVD), which results in multi-stimuli responsive core-shell nanorods. These nanorods are deposited into a template material (UV-curable Polyurethane acrylate). The template material is deposited onto flexible PET substrates and is subsequently patterned using UV-NIL techniques. Electrical characterization of the resultant device is required to quantify the response to humidity, temperature and pressure, which is accompanied by FEM simulations.
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Microbiologically influenced corrosion (MIC) of steel - A study using correlative SEM, EDX and Raman microscopy Abstract: Direct costs due to corrosion worldwide amount to 3% and in some countries up to 5% of the GDP (gross domestic product). Secondary cost like production losses or efficiency loss can be much higher. Apart from these enormous costs and the economic consequences, in many areas, corrosion represents a very high safety risk (e.g. aircraft and pipelines). Microbiologically influenced corrosion (MIC) is responsible for 20% of all corrosion damage. 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, while others speed it up. It is important to note that one of the difficulties in understanding MIC is that the composition of bacterial cultures and biofilms can vary greatly. This makes any newly discovered composition an interesting topic to study.
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Analysing Tunneling Current-Voltage Characteristics in Molecular Junctions Abstract: When characterizing molecular and monolayer junctions one of the key-parameters used is the so-called transition voltage Vt. Its relation to the intrinsic electronic properties of the junction is still poorly understood, although Bâldea, Frisbie and coworkers[1] have recently obtained an excellent correlation between the energetic positions of the electronic transport channels extracted from a simple onestate model and the positions of the peaks in the density of states obtained via photoelectron spectroscopy measurements. This raises the question, to what extent a model building on a single, discrete energy level can be sufficient to represent the complex electronic structure of the junction. We investigated the applicability of the aforementioned model especially in view of the vastly different coupling strength between substrates and molecules upon changing the docking chemistry.
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Understanding Phonon Properties in Metal-Organic Frameworks From First Principles Abstract: Metal-organic frameworks (MOFs) have been extensively studied during the last years due to their numerous possible applications exploiting the large amount of internal surface area (e.g. catalysis, storage, capture and separation of gases). Due to the relatively new trend to employ MOFs in functional devices [1-3], researchers have been gradually becoming more interested in their functional properties, many of which are typically dominated by contributions of phonons – i.e. quasi-particles of lattice vibration with energy and momentum. However, vibrational properties in MOFs, despite their importance for describing practically relevant quantities like thermal conductivity [4], mechanical behaviour [5], or thermal expansion [6], are still largely unexplored. Here, the phonon picture provides a convenient framework to associate various materials properties with individual vibrational modes and helps to understand why certain properties can be observed. By exploiting knowledge about the phonons, specific building blocks can be combined to engineer phonon band structures and the resulting properties. Therefore, we studied the influences of different constituents on the (an)harmonic vibrational properties of a variety of MOFs by means of atomistic simulations. We systematically varied the metallic nodes and organic linkers in isoreticular MOFs (IRMOFs) to separately explore their influence on the phonon dispersion and the resulting properties. The goal of our study is to deduce structure-to-property relationships for phonon-related properties in MOFs: differences in physical observables (thermodynamic quantities, elastic constants, etc.) are explained by comparing vibrational modes amongst the studied systems and rationalising frequency shifts by structural arguments. Clear trends in the changes of phonon band dispersion and spatial localisation of modes can be observed. Our simulations have been performed in the framework of density functional theory using the PBE functional [7] and self-consistent charge density functional tight binding [8].
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Material model for pulp fibres Abstract: Mechanical characteristics of paper is for increasing performance demands in industrial applications of high relevance. However, the mechanics of paper is very difficult to predict, since it consists of an unordered network of fibres. Additionally, very less is known about the mechanics of the pulp fibres it consists of. This study aims to give deeper quantitative insight into the relaxation phenomena of individual pulp fibres. For that we propose a minimal continuum representation and parameter estimation method. Finally, this model can be used as a subpart of a network simulation and predict unwanted deformations in high speed printing applications.
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U-Joining of additively manufactured composite-metal hybrid parts: An innovative approach Abstract: One of the main strategies applied by the transportation industry to improve products’ energy efficiency is the application of lightweight alloys and engineering polymers or composites. Combining these dissimilar materials allows unique solutions for engineering requirements; however, it also demands advanced assembly techniques to allow the adequate combination of their positive properties, such as the high mechanical strength of Ti-6Al-4V alloy and the low density of CF-PEEK. Nonetheless, joining these materials also represents a great challenge, since dissimilar materials can have extreme differences in their properties. Ultrasonic Joining (U-Joining) is a recently developed solid-state joining process which has been shown suitable to produce hybrid joints between conventionally manufactured metals and thermoplastic-based materials. Since Additive Manufacturing (AM) processes have been gaining momentum on their industrial applications, there are an unexplored field which can provide innovative solutions to the implementation of U-Joining: the joining of additively manufactured composite-metal hybrid parts. The use of AM processes allows the production of parts with complex designs using topology optimization, which can be assembled together using the U-Joining process. This work aims to develop, manufacture and evaluate the mechanical performance of additively manufactured aircraft composite-metal hybrid structures produced by U-Joining.
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Surface Crystallization Studies of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) Abstract: Benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives are very promising candidates in the field of solution processable organic semiconductors. 1 In this work the surface crystallization behaviour of Ph-BTBT-10 is investigated. Thin films starting from the monolayer regime up to thick films were prepared by spin coating and physical vapour deposition. The films were investigated in terms of crystalline properties and thin film morphology by X-ray diffraction, X-ray reflectivity and Grazing Incidence X-ray diffraction, atomic force microscopy and optical microscopy. It is shown that by spin coating at low concentrations of 0.3 g/l an incomplete monolayer of standing molecules with the aromatic core pointing towards the substrate is formed. At higher concentrations between 0.5 g/l and 3 g/l strong island growth starts which leads to the formation of macroscopic islands with dendritic monolayers in-between them. Physical vapour deposition demonstrates a more homogenous distribution of the material forming terraces of multiple molecules. In thin films whether in solution or PVD crystalline structures are observed in XRD. As well as the known bulk phase with a head to head arrangement of two molecules in an orthorhombic unit cell possessing a herringbone structure, also other polymorphic phases are present.
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55 posters.