TU Graz
Graz University of Technology

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.

Schedule

 Welcome 9:00 - 9:20 09:00 - 09:20 Advanced Materials Day OnlineHorst Bischof, Anna Maria Coclite, Gregor Trimmel, Christof Sommitsch
 3D - Printing 10:10 - 10:55Moderator: Sergio AmancioPoster Location: Stremayrgasse 16, BMTEG069 Influence of bed surface on the mechanical performance of CF-PA6 parts printed by FFFCarlos Belei, Institute of Material Science, Joining and Forming – BMK Endowed Professorship for Aviationhttps://cloud.tugraz.at/index.php/s/MtBB5XJfASMcMmqAbstract: 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. Microstructure analysis of additive manufactured CF-PA6 parts under consideration of different consolidation parameters. Hannes Oberlercher;, Institute of Material Science, Joining and Forming – BMK Endowed Professorship for Aviationhttps://fhkarnten-my.sharepoint.com/:b:/g/personal/oberlercher_fh-kaernten_at/EaIPzt04CuFBkbnPOkUwhLMBXNowPB5SYJ6ZlmTPOY8HDA?e=BllczKAbstract: 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. [1] Henninger, F. 1998. Deconsolidation behaviour of glass ﬁbrepolyamide 12 composite sheet material during post-processing. Plastics rubber and composites processing and applications. 1998, 27.6. Expanding 3D Nano-Printing Performance by Blurring the Electron BeamLukas Seewald, Institute of Electron Microscopy and Nanoanalysis (FELMI), Graz University of Technology, 8010 Graz; Christian Doppler Laboratory https://cloud.tugraz.at/index.php/s/i6zspT6H9FWHqdDAbstract: 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. [1]Winkler, R., Fowlkes, J. D., Rack, P. D. & Plank, H. 3D nanoprinting via focused electron beams. J. Appl. Phys. 125, 210901 (2019) [2]Plank, H. et al. Focused electron beam-based 3D nanoprinting for scanning probe microscopy: A review. Micromachines 11, (2020) [3]Plank, H., Gspan, C., Dienstleder, M., Kothleitner, G. & Hofer, F. The influence of beam defocus on volume growth rates for electron beam induced platinum deposition. Nanotechnology 19, 485302 (2008) Electron beam freeform fabrication of NiTi shape memory alloys Rafael Paiotti M. G. , IMAThttps://cloud.tugraz.at/index.php/s/HcBCeLY7Hr8P5ntAbstract: 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. In situ structural analysis of AlSi$_{10}$Mg for additive manufacturing – from powder to thermally treated partsRobert Krisper, Felmi-ZFEhttps://cloud.tugraz.at/index.php/s/iiZ27cRWR9GBd93Abstract: 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. Friction Surfacing as an alternative additive manufacturing technique for titanium alloysStefan Fortmueller, Institute of Materials Science, Joining and Forminghttps://www.dropbox.com/s/mvj07cay2a8zqnm/Poster_AMD2020_Fortmueller.pdf?raw=1Abstract: 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. Expanding Capabilities of Focused Electron Beam Based 3D Nano-Printing: From Meshes Towards Closed 3D Nano-ArchitecturesAnna Weitzer, Institute of Electron Microscopy and Nanoanalysis (FELMI), Graz University of Technology, 8010 Grazhttps://cloud.tugraz.at/index.php/s/R2JEy7QZX2Qfn5iAbstract: 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. References: [1] Winkler, R.; Fowlkes, J. D.; Rack, P. D.; Plank, H. 3D Nanoprinting via Focused Electron Beams. J. Appl. Phys. 2019, 125, 210901. [2] Fowlkes et al., High-Fidelity 3D-Nanoprinting via Focused Electron Beams: Computer-Aided Design (3BID), ACS App. Nano Mat. 2018, 1 (3), 1028.

### Coffee Break

 Porous Materials 11:15 - 12:00Moderator: Paolo FalcaroPoster Location: Petersgasse 16, Physics Building, TDK Foyer Investigation on the influence of alkyl ligands of zinc xanthate complexes on the formation and porosity of ZnS thin filmsEfthymia Vakalopoulou, Institute for Chemistry and Technology of Materialshttps://cloud.tugraz.at/index.php/s/MdNcKZ3nN2MkPHL/downloadAbstract: 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] Our research is focused on the synthesis of zinc xanthate complexes with different alkyl ligands and subsequently their use for the formation of metal sulfide thin layers via a solution-based method. The study shows that the xanthate ligands have a great influence on the film formation process as well as the film porosity. The properties and features of the thin films before and after zinc xanthates’ decomposition are investigated via several techniques such as FT-IR spectroscopy, X-ray reflectivity, dynamic GISAXS/GIWAXS and scanning electron microscopy (SEM). [1] T. Rath, M. Edler, W. Haas, A. Fischereder, S. Moscher, A. Adv. Energy Mater. 2011, 1, 1046–1050. [2] C. Buchmaier, M. Glaenzer, A. Torvisco, P. Poelt, K. Wewerka, B. Kunert, K. Gatterer, G. Trimmel, T. Rath, J. Mater. Sci. 2017, 52, 10898-10914. Deposition of Ion Conductive Membranes from Ionic Liquids via Initiated Chemical Vapor DepositionMarianne Kräuter, Institute of Solid State Physicshttps://cloud.tugraz.at/index.php/s/CotPz6bi9FZmSSd/downloadAbstract: 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. In this study, liquid droplets of 1-allyl-3-methylimidazolium dicyanamide have been processed by initiated chemical vapor deposition (iCVD) with a cross-linked polymer film consisting of (hydroxyethyl)methacrylate and ethylene glycol dimethacrylate, in order to develop freestanding, ion-conductive membranes. We found that the obtained films are solid and have a conductivity of up to (18 ± 6) mS/cm, associated to the negatively charged counter ion, indicating no loss of the original conductivity in their liquid state. The membranes are conductive within a large process window and in air, thanks to the fact that the iCVD process does not affect the mobility of the anion in the ionic liquid. Furthermore, we demonstrate that varying the deposition conditions can influence the homogeneity and conductivity of the resulting membranes. Our results showcase the potential of conductive membranes synthesized from ionic liquids via iCVD and illustrate their stability over a large process window. The promising results of this study represent an important stepping stone on the way to novel ion conductive membranes. Insights into dealloying from in-situ magnetometryMarkus Gößler, Institute of Materials Physicshttps://cloud.tugraz.at/index.php/s/cLFPc9jzH6C7rsKAbstract: 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]. [1] J. Erlebacher et al., Nature 410, 450–453 (2001) [2] M. Goessler et al., J. Appl. Phys. 128, 093904 (2020) In situ monitoring of the formation and orientation of mesopores in H1-ePt films by GI-SAXS during templated electrodepositionPhilipp Aldo Wieser, Institute of Inorganic Chemistry, Graz University of Technology, Graz, Austriahttps://cloud.tugraz.at/index.php/s/cPzndcH9RQd2ApiAbstract: 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. Previous studies [1, 2] showed that the resulting H$_1$-e palladium and platinum films contain regular hexagonal arrays of cylindrical pores separated by platinum or palladium walls with a centre to centre distance of 5-6 nm. These films exhibit very high surface areas in the order of up to 91 m$^2$/g. The high surface area of the mesoporous films and the ability to control pore structure and accessibility enable their successful application in fields such as catalysis, analysis separation technology, optical devices, and biomedical science. The application of GISAXS in combination with the brilliant synchrotron radiation source ELETTRA-Sincrotrone Trieste enables in situ monitoring of the formation, structure and orientation of the mesopores in the films. [1] Attard, G. S., et al. “Mesoporous Platinum Films from Lyotropic Liquid Crystalline Phase.” Science 278 (1997) 838-840. [2] Bartlett, P. N., et al. "The preparation and characterization of H 1-e palladium films with a regular hexagonal nanostructure formed by electrochemical deposition from lyotropic liquid crystalline phases." Physical Chemistry Chemical Physics 4 (2002): 3835-3842. Revealing the photo-triggered structural dynamics of photo-responsive Metal-Organic Frameworks grown on oriented heteroepitaxial ceramic thin films Sumea Klokic, Institute of Inorganic Chemistryhttps://drive.google.com/file/d/1z2h-uHDFapu_vyrqvhzkRLmdXjWOuInm/view?usp=sharingAbstract: 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. Based on a previously described procedure to obtain centimetre-scale oriented MOF films, an automated, operator-independent deposition method of crystalline copper hydroxide nanobelts is under development [1]. This automatic method introduces the possibility for large-scale thin-film processing of aligned nanobelts with preferential orientation on various substrates. These ceramic thin films can be further converted to three-dimensional flexible MOFs, such as DMOF-1 [2,3]. Infiltration of this framework with suitable chromophores implements a photo-responsive functionality. Hence, we successfully infiltrated the flexible framework DMOF-1 by azobenzene as the appearance of characteristic vibrational bands were investigated by ATR and Raman spectroscopy. The main focus of our research aims to elucidate the photo-triggered processes in this class of materials, accordingly pump-probing of these photo-switchable frameworks in combination with Grazing-Incidence Small Angle X-Ray Scattering experiments are currently pursued to track structural dynamics in solids at the timescale of such. At the ps-pump probe station at the Austrian SAXS beamline we successfully pumped the infiltrated thin films grown on glass substrates by UV light (342 nm) and induced the forward switching of the flexible thin crystalline film, whilst the recovery of the system was achieved by illumination at 435 nm. Photo-switching of the infiltrated azobenzene forces the flexible framework to adapt to the trans/cis isomerization, thus undergoing a change in its crystalline phase. Hence, the structural transitions of the crystalline film upon photo-switching were pursued over time by probing the evolution of the Bragg reflections with X-Rays. These findings proved for the first time the reversible photo-switching of MOF thin films accompanied by structural changes. [1] (a) Falcaro, P.; Okada, K.; Hara, T.; Ikigaki, K.; Tokudome, Y.; Thornton, A. W.; Hill, A. J.; Williams, T.; Doonan, C.; Takahashi, M.; Falcaro, P. Nature materials 2017, 16, 342. (b) Klokic, S.; Linares-Moreau, M.; Carraro, F.; Falcaro, P.; publication in progress. [2] Yanai, N.; Uemura, T.; Inoue, M.; Matsuda, R.; Fukushima, T.; Tsujimoto, M.; Isoda, S.; Kitagawa, S.; J. Am. Chem. Soc. 2012, 134 (10), 4501–4504. [3] Ikigaki, K.; Okada, K.; Tokudome, Y.; Toyao, T.; Falcaro, P.; Doonan, C.J.; Takahashi, M. Angewandte Chemie 2019, 131, 6960. Functional Biodegradable Polymer-based 3D Scaffolds: Fabrication, Characterization and Application in Tissue Engineering Applications Tamilselvan Mohan*, Rupert Kargl, Karin Stana Kleinschek*, Institute of Chemistry and Technology of Biobased System (IBioSys), Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria.https://cloud.tugraz.at/index.php/s/5fganYTgWR5xN49Abstract: 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. References: [1]. T. Mohan, A. Dobaj Štiglic, M. Beaumont, J. Konnerth, F. Gürer, D. Makuc, U. Maver, L. Gradišnik, J. Plavec, R. Kargl and K. Stana Kleinschek, ACS Applied Bio Materials, 2020, 3, 1197-1209. [2]. M. Milojeviæ, L. Gradišnik, J. Stergar, M. Skelin Klemen, A. Stožer, M. Vesenjak, P. Dobnik Dubrovski, T. Maver, T. Mohan, K. Stana Kleinschek and U. Maver, Applied Surface Science, 2019, 488, 836-852. Implications of pulp fiber porosity on material modellingTristan Seidlhofer, Institute of Bioproducts and Paper Technology, Institute of Strength of Materialshttps://cloud.tugraz.at/index.php/s/JnC9ifYkcm6Wcyt/downloadAbstract: 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.

### Lunch Break

 Gründungsgarage 13:20 - 13:30Moderator: Anna Maria CoclitePoster Location: Petersgasse 16, Physics Building, TDK Foyer Gründungsgarage: The Academic Startup Accelerator!Romana Höberl, Gründungsgaragehttps://yeea.qloc-cloud.de/s/n3SazyNCyGWF6CKAbstract: We are constantly looking for motivated teams with innovative business ideas. With the support of mentors from business and science, together with our expertise, we offer the ideal opportunity to help start-ups get off to the right kick start and support them on their way to their own business. At the beginning of each semester, students and academic staff have the opportunity to apply with their concrete business ideas. From all ideas submitted, 10 will be selected to be accompanied throughout the semester. During these few months, the team of the Gründungsgarage and the mentors will provide individual coaching hours, workshops and Pitchtrainings with a consulting value of 50.000€ to support the start-ups in the best way.
 Spectroscopy and Microscopy 15:40 - 16:10Moderator: Werner GroggerPoster Location: Petersgasse 16, Physics Building, TDK Foyer Femtosecond Photoexcitation Dynamics of Atoms and Molecules inside Helium NanodropletsBernhard Thaler, Institute of Experimental Physicshttps://drive.google.com/file/d/19Z4Zed475XlVjvumUX8l3ibJgN02HrZC/view?usp=sharingAbstract: 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. In the case of In atoms, photoexcitation triggers an expansion of the He bubble within 600 fs, which is represented by a 300 meV shift of the photoelectron kinetic energy (Fig. 1a) [1]. Simulations reveal that In excited-state electronic energy is converted into He kinetic energy (pressure waves) during this process. The bubble expansion is followed by an oscillation of the He bubble with a period of (28±1) ps, and ultimately leads to ejection of the dopant from the droplet after ~60 ps. In the case of In2, photoexcitation initiates a very similar response of the He solvent (Fig. 1b) [2]. Superimposed we find a strong periodic modulation of the photoelectron signal, indicating coherent nuclear wave packet (WP) motion of In2 with a 0.42 ps period. The slowly decaying periodic signal reappears after 150 and 300 ps, representing the half and full revivals of the WP, respectively. Appearance of these revivals demonstrates that the He-induced influence on coherent nuclear motions can be lower by a factor of 10-100 compared to conventional solvents. [1] B. Thaler, S. Ranftl, P. Heim, S. Cesnik, L. Treiber, R. Meyer, A. W. Hauser, W. E. Ernst, M. Koch, Femtosecond photoexcitation dynamics inside a quantum solvent, Nat Commun 9, 4006 (2018) [2] B. Thaler, M. Meyer, P. Heim, M. Koch, Long lived nuclear coherences inside helium nanodroplets, Phys. Rev. Letters 124, 115301 (2020) In situ temperature control in Raman microscopy – Hot or Not?Harald Fitzek, Institute of Electron Microscopy and Nanoanalysis (FELMI)https://cloud.tugraz.at/index.php/s/KnMmx4KbESnCwBKAbstract: In the last year, students had the following task at our advanced lab exercise: “In our current laboratory exercise research project, we are trying to reactivate a heating/cooling stage for in situ heating experiments that has not been used at our institute for a while. The stage when fully equipped is build for temperature from liquid nitrogen cooling up to about 500 K. In each lab exercise, we will focus on two things. First to setup an additional part of the stage and second to produce some in situ results on interesting samples. Our goal is to demonstrate that even in the limited time available during a lab exercise it is possible to gradually setup new experimental equipment and produce good quality results.” In several lab exercises we have fully activated the heating/cooling stage and its entire temperature range is now available. In addition we have analyzed the behavior of several samples as a function of temperature, focusing on intrinsic changes, destruction of the sample at high temperatures and the sensitivity to the laser beam. On this poster, we will present a selection of the most interesting results of each of the four groups that participated in the exercise. Precise measurements of potassium ions with Fourier transform spectroscopyKazma Komatsu, Institute of Experimental Physicshttps://drive.google.com/file/d/1WC-jZv6PVUCDRu3Q24NOXaz_aw2kZYhM/view?usp=sharingAbstract: 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. In this study, we investigate multi-photon ionization process of potassium driven by a high intensity laser source. By combining the supreme spectral resolution of DCS with high intensity lasers we can obtain information on electronic excitation in the potassium atom before ionization with a resolution only limited by the intrinsic linewidth of the resonances. Besides, with the comparably low pulse energy of our lasers we can achieve intensities sufficient to access the nonlinear regime of multi-photon ionization. We realize this with extremely tight focusing to ~ $2$ µm corresponding to an intensity of $> 10^{12}$ W/cm$^2$. Throughout the study, we will provide the deeper understanding of the excitation followed by ionization of potassium and potentially investigate the vibrational wavepacket dynamics of K$_2^+$ ions. Differential Phase Contrast Imaging in Scanning Transmisson Electron MicroscopyThomas Radlinger, Institute of Electron Microscopy and Nanoanalysis https://cloud.tugraz.at/index.php/s/Xgz5JKPkNRtbxWkAbstract: 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. Ultrafast control of helicity dependent electron dynamics in molecules and solidsZhenhao WANGhttps://1drv.ms/b/s!Ahthsev5X2HBhM5ATVeam96j5xvNXQ?e=UivzdMAbstract: 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.
 Physics Doctoral School 16:10 - 17:30Moderator: Markus AichhornPoster Location: Petersgasse 16, Physics Building, P2 Foyer Conceptual studies for a future collider beam dumping systemAlexander Krainer, CERN, TU Grazhttps://cernbox.cern.ch/index.php/s/2IEll0gH3DpipynAbstract: 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]. Even though particle energies between 45.6 GeV and 182.5 GeV are not on the energy frontier, beam intensities of up to $2.8*10^{15}$ particles per beam are unprecedented. This poses new challenges to every part of a particle accelerator. A key requirement to safely operate such a machine is the ability to dispose of the beam when necessary. The main factors for designing such an extraction and dumping system are safety, reliability but also availability. In the first Conceptual Design Report for the FCC-ee, which was submitted to the European Strategy Group for Particle Physics in 2019, the beam dumping system was focused mainly on a high energy hadron collider and therefore much more complex. Especially the complex active dilution of the beam onto an absorber block poses technical challenges and could be a potential point of failure. Furthermore, to achieve this dilution a 2.8 km long extraction tunnel was foreseen [3]. To increase reliability and remove potential failure cases, a new, passive beam dilution system is designed. The idea is to use multiple-coulomb scattering of particles in materials as a means of diluting the beam. However, the dimensions, shape and materials used have to be considered carefully to ensure longtime survivability of the diluter. When passing through the diluter, the beam deposits up to 16.5 kJ inside the material within 250 us. In combination with the “flat” transversal beam shape that is foreseen for the FCC-ee, this creates huge thermomechanical stresses within the material. It is therefore essential to study these beam impacts and the material response via simulations and experiments. To simulate the beam impact and the deposited energy in the material, the Monte-Carlo particle transport code FLUKA is used [4, 5, 6]. The results are then used to simulate the dynamic response of the material with the Finite Element Solver codes Ansys and LS-Dyna [7]. To evaluate the quality of the simulation results, an experiment at the CERN HiRadMat Facility [8] is foreseen for 2021. [1] FCC Homepage, Sep. 2020, url: https://fcc.web.cern.ch. [2] M. Benedikt et al. “FCC-ee: The Lepton Collider”, Eur. Phys. J. Spec. Top. 228, 261–623 (2019). https://doi.org/10.1140/epjst/e2019-900045-4 [3] M. Benedikt et al. “FCC-hh: The Hadron Collider”, Eur. Phys. J. Spec. Top. 228, 755–1107 (2019). https://doi.org/10.1140/epjst/e2019-900087-0 [4] FLUKA Homepage, Sep.2020, url: https://fluka.cern [5] G. Battistoni et. al. "Overview of the FLUKA code", Annals of Nuclear Energy 82, 10-18 (2015). [6] T.T. Bohlen et. al. "The FLUKA Code: Developments and Challenges for High Energy and Medical Applications", Nuclear Data Sheets 120, 211-214 (2014). [7] Ansys Mechanical and Ansys LS-Dyna, Release 2020 R2 [8] N. Charitonidis, A. Fabich and I. Efthymiopoulos, "HiRadMat: A high-energy, pulsed beam, material irradiation facility," 2015 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), Lisbon, 2015, pp. 1-3, doi: 10.1109/ANIMMA.2015.7465596. Strongly correlated quantum transport systems in non-equilibriumAndrei-Viorel Man, Institute of Theoretical Physics and Computational Physicshttps://cloud.tugraz.at/index.php/s/fGCyKKdCqxp7Ee2Abstract: 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. Structural transitions of organic polymorphs on metal surfacesAnna Werkovits, Institute of Solid State Physicshttps://cloud.tugraz.at/index.php/s/tZFJNdCAYiXooKMAbstract: 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. [1] L. Hörmann et al., Comput. Phys. Commun. 244, 143-155 (2019) Non-destructive analytical determination of coated wood, paper and composite surfaces by combining AFM with spectroscopic methodsElisabeth Anna Schöffmannhttps://www.dropbox.com/s/21cj53k8vo5lu8a/20200909_Poster_Sch%C3%B6ffmann.pdf?raw=1Abstract: The aim of this PhD thesis is the development of a non-destructive analytical determination technique for coated wood, paper and composites by combining Atomic Force Microscopy (AFM) with spectroscopic methods, especially infrared spectroscopy. These methods allow to obtain information from different depths of the samples. Using non-destructive methods it is questionable which chemical and physical information (e.g. molecule structure, bonding, rigidity, roughness) can be obtained. Hence, by obtaining signals at different depths, different information can be gathered which allows a de>>>ion of samples-under-test at a macroscopic level. Different coated wood, paper and composite samples with different numbers of coating layers and coating material curing-grades will be examined and their influence on the samples will be investigated through experimental validation. Finally, a correlation of macroscopic properties between current state-of-the-art destructive testing methods and the proposed non-destructive method based on the gathered data will be investigated. The work is conducted at the Wood K plus in St. Veit an der Glan together with Graz University of Technology. Long-Range Correlations and Magnetic Ordering in Pyrochlore-IridatesJohannes Graspeuntner, Institute for theoretical and computational physicshttps://cloud.tugraz.at/index.php/s/SCRGxket53CpbNaAbstract: 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 first identify the minimal low-energy model that is necessary to describe the relevant electronic states around the Fermi level. A main part of this thesis is planned to be spent on the effect of non-local correlations on the electronic, and most importantly, topological properties of Pyrochlore iridates. There are two routes to be taken. First, we can include short-ranged non-local correlations via the cluster extension of the dynamical mean-field theory, and second, we will study long-ranged correlations using a diagrammatic extension of DMFT, which is the TRILEX approach. This work will not only help understanding the properties if these materials, but will also be an important step forward in the applications of beyond-DMFT methods for real materials calculations. Effects of phonons in strongly correlated systems out of equilibrium: application to Mott photovoltaicsPaolo Gazzaneo(1), Max Sorantin(1), Antonius Dorda(1), Karsten Held(2) and Enrico Arrigoni(1), (1) Institute of Theoretical and Computational Physics, TU Graz, 8010 Graz, Austria - (2) Institute of Solid State Physics, TU Wien, 1040 Vienna, Austriahttps://cloud.tugraz.at/index.php/s/p488S49FHCMWdpe/downloadAbstract: 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. [1] Kalcheim, Y., Camjayi, A., del Valle, J. et al., Nat Commun 11, 2985 (2020). [2] E. Assmann, P. Blaha, R. Laskowski, K. Held, S. Okamoto, G. Sangiovanni, Phys. Rev. Lett. 110, 078701 (2013). [3] E. Janod, J. Tranchant, B. Corraze, M. Querré, P. Stoliar, M. Rozenberg, T. Cren, D. Roditchev, V. T. Phuoc, M.-P. Besland, L. Cario, Advanced Functional Materials 25, 6287-6305 (2015). [4] Y. Murakami, P. Werner, N. Tsuji, H. Aoki, Phys. Rev. B 91, 045128 (2015). [5] E. Arrigoni, M. Knap, W. von der Linden, Phys. Rev. Lett. 110, 086403 (2013). [6] M. E. Sorantin, A. Dorda, K. Held, E. Arrigoni, Phys. Rev. B 97, 115113 (2018). Transition Metal Chalcogenides under Extreme Pressures: Material Properties from First-Principles CalculationsRoman Lucrezi, Institute of Theoretical and Computational Physicshttps://cloud.tugraz.at/index.php/s/EyDxj4JgyXoWKi5Abstract: 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. In this research project, we combine several fully ab initio and state-of-the-art methods in order to search for new high-pressure structures, determine electronic and vibrational properties of stable structures, as well as to calculate their electron-phonon coupling (EPC), superconducting properties, and instabilities towards charge-density wave ordering. Here, the focus is on the main strategy and methods we apply to find new materials with fascinating properties, including some examples of ongoing research in the Nb-S system. [1] W. Tremel et al., J. Alloys Compd. 219, 73 (1995) [2] X. Zhou et al., Chem. Mater. 29, 14, 5737 (2017) [3] C. Heil et al., Phys. Rev. Lett. 119 , 087003 (2017) [4] R. A. Klemm, Physica C 514, 86 (2015) Understanding heat transport in metal-organic frameworks in real and reciprocal spaceSandro Wieser, Institute of Solid State Physicshttps://cloud.tugraz.at/index.php/s/E6CxwfGdFMPrtbcAbstract: 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. So far molecular dynamics simulations for isoreticular MOFs show that a major bottleneck for heat transport in MOFs is represented by the connecting bonds between node and linker. The impact of this thermal interface can be tuned by adjusting the mass of the metal atoms or by changing the metal-oxygen bond strength. Prior to carrying out these computationally demanding simulations, it was necessary to parameterize high-quality classical force fields based on ab-initio reference data, which will continue to be performed for all further materials of interest. The previous findings should now be expanded by considering a different set of materials, MOF-74 and its derivatives, which show a completely different node-linker bonding chemistry. Similar molecular dynamics simulations in non-equilibrium will be carried out in order to determine the significance of the thermal interfaces between node and linker for a selection of different materials. Heat transport in materials with low charge transport is dominated by phonons. A key goal for the further analysis is to evaluate the contributions of individual lattice vibrations toward the thermal conductivity. This will be achieved by complementary analysis of data obtained from molecular dynamics simulations (in real space) and lattice dynamics simulations (in reciprocal space). This will ultimately lead to the identification of crucial phonons for heat transport based on variations in the atomistic structure and bonding chemistry advancing the fundamental understanding of the mechanism of heat transport processes in MOFs. Consequently, this will allow tailoring of materials with specific heat transport requirements desired for individual applications. High-temperature superconductivity in SuperHydrides at extreme pressuresSimone Di Cataldo, Graz University of Technology, Sapienza University of Romehttps://www.dropbox.com/s/evchcje7ptjq4zk/DiCataldo_Poster.pdf?raw=1Abstract: 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]. [1] J. A. Flores-Livas, L. Boeri, A. Sanna, G. Profeta, R. Arita, and M. Eremets, Physics Reports 856, 1-78 (2020) [2] C. Heil, S. Di Cataldo, G. B. Bachelet, L. Boeri, Phys. Rev . B 99, 220502(R) (2019) [3] S. Di Cataldo, W. Von der Linden, L. Boeri, Phys. Rev. B 102, 014516 (2020) Ultrafast Charge and Spin Control in Nanoengineered DevicesThomas Jauk, Institute of Experimental Physicshttps://drive.google.com/file/d/1cXuhw6-b9GHwJ9ltf_IblK1dGUGYqc9b/view?usp=sharingAbstract: 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. [1] Siegrist, F. et al. Light-wave dynamic control of magnetism. Nature 571, 240–244 (2019). Orbital Mapping by STEM-EELSMichael Oberaigner, Institute of Electron Microscopy and Nanoanalysis (FELMI)https://cloud.tugraz.at/index.php/s/nLtSzpDdrdsgxrP/downloadAbstract: 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. This FWF-funded PhD-project tries to overcome these visualization issues. The symmetry problem will be approached by performing measurements close to interfaces, defects or crystal with low symmetry. The SNR issue can hopefully be tackled by working with the latest generation direct-electron detectors used for STEM-EELS experiments. The influence of other experimental parameters such as sample thickness, acceleration voltage, aperture sizes, dispersion, etc. will also have to be tuned to optimize feature visibility. Further, a robust workflow for post-processing spectrum images with low SNR will be developed. [1] S. Löffler et al, Ultramicroscopy, 177 (2017), p. 26–29 Cylindrical gas-gap capacitor structure: Performance and reliability of gas-gaps within semiconductor devicesPeter Oles, Institute of Solid State Physicshttps://cloud.sieberer.me/f/1398e76bd442408aa6ed/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. For our research, we design and manufacture a cylindrical capacitor structure as our test vehicle. This capacitor is investigated by electrical measurements as well as electro-mechanical simulations. From these investigations we aim to derive a physical model to correctly predict the leakage current. Based on this model we expect to be able to correctly predict the behavior and evolution of micro- and nanometer gas gaps in semiconductors at high electric fields in general.