Adrian Kirchner
The ultraviolet (UV) spectral region is home to highly relevant electronic transitions but remains underexplored due to a lack of suitable light sources and high-resolution spectrometers. A new generation of high-power frequency combs allows dual-comb spectroscopy (DCS) to access this range by nonlinear frequency upconversion, offering high resolution and short acquisition times. Utilizing resonant dispersive wave (RDW) emission in a gas-filled hollow-core fiber, an agile light source with 20 nm (FWHM) bandwidth and tunability from ~340 nm to 465 nm is created. The process conserves the coherence of the driving comb and has high conversion efficiencies of (1.5 +- 0.4)%. To display the capabilities of RDW, absorption spectroscopy of NO2 is performed. The talk will end with a perspective on pushing DCS to even higher photon energies via high-harmonic generation in a gas target.
Isabella Kohlhauser
Climate models are a fundamental source of climate change information. So-called general circulation models (GCMs) provide a good representation of large-scale processes in the climate system, nevertheless regional climate models (RCMs) are an essential tool to
provide local, smaller-scale information. Especially in regions with complex topography, like the European Alps, high-resolution data is necessary to provide trustworthy regional climate change projections. In recent years, the availability of computational resources enabled the rise of so-called convection-permitting models (CPMs), which operate at the kilometer-scale and surpass the level of detail given from traditional RCMs. This generation of models is known to improve the representation of short-term precipitation extremes and related climate change phenomena, which is why these measures are usually the center of attention in literature. Temperature related processes are rarely evaluated, usually only in the context of extremes, and systematic shortcomings are therefore often overlooked. In our project
HighResMountains we exploit several available high-resolution temperature data sources in Austria and Switzerland, and investigate the representation of temperature measures, such as the diurnal temperature range and elevation dependence. We find significant uncertainties in recent convection-permitting simulations and try to identify potential causes for mismatches with observational data through physical processes in the models.
Christoph Wachter
Numerous properties of organic/metal interfaces strongly depend on their polymorphism. To computationally predict the thermodynamically most stable polymorph at finite temperature and pressure, the state-of-the-art method is ab initio thermodynamic. However, several approximations made within ab initio thermodynamics have been developed with small inorganic adsorbates in mind, which are comparable in size to a substrate unit cell and have no or only a few internal degrees of freedom, and it is unclear how well these approximations translate to larger, more complex organic adsorbates.
In this talk we first discuss the challenges one faces when attempting to go beyond the common approximations of ab initio thermodynamics. Afterwards, we re-evaluate these approximation for organic adsorbates using the model system of tetracyanoethylene (TCNE) on Cu(111) to elucidate whether precise computational phase diagrams for organic/metal interfaces require additional effort.
Robbin Steentjes
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are renowned for their simplistic and modular crystal structure. They are often said to behave ‘like LEGO®’, combining organic linkers and nodes into predictable patterns. Since it is difficult to grow large MOF and COF crystals, mostly powders are synthesized, for which powder X-ray diffraction (PXRD) experiments are an accessible but ambiguous characterization technique. Subtle differences, like disordered stacking, are difficult to deduce from PXRD experiments. We can, however, exploit the ease of simulation of such experiments to perform calculations on virtual crystals with hypothetical stacking configurations. We do this to identify trends relating PXRD patterns to stacking modes. We then use ab-initio calculations, to generate models that contain disorder in the stacking arrangement. These models contain a greater complexity and higher physical accuracy than previously proposed models, and can serve as the basis for more accurate theoretical property determination of 2D stacked MOFs and COFs.
Lara Marie Novak
Nanoporous gold (npAu) prepared by electrochemical dealloying serves as an ideal platform for sensing applications due to its self-standing, conductive structure and high surface-to-volume ratio. By tuning the pore size and modifying the surface with covalently bound self-assembled monolayers (SAMs), highly versatile electrode materials can be generated. Suitably selected SAMs also enable the binding of active enzymes for biosensing and catalysis. Two different examples of this electrode design approach are presented here:
(i) In order to selectively detect fluoride anions in water, nanoporous gold was modified with a boronic acid terminated SAM. Upon binding of F−, the boronic centre altered its charge state, thereby changing the electrodes surface potential. Exposing the modified npAu electrodes to a step-wise increasing fluoride concentration led to immediate and well-defined changes of the measured potential, which were well reproducible even after regeneration in alkaline media [1].
(ii) Immobilization of enzymes on (nano)porous metal carriers provides the foundation for an advanced design of bio-electrodes suitable for catalysis and sensing. To obtain efficient coupling of the enzymes to the electrode surface, a fundamental understanding of the interaction between enzyme and carrier is crucial. Therefore, the well-studied L-lactate oxidase (LOx) was chosen as a model enzyme and immobilized on npAu modified with several different SAMs. The activity and operational stability of the resulting enzyme electrodes was studied as a function of carrier geometry (planar/nanoporous, varying pore size) and surface characteristics (surface charge, hydrophilicity/hydrophobicity). The findings obtained in this study are applicable to a multitude of enzymes, and thereby facilitate the design of a diverse array of nanoporous metal-based bioelectrodes.
This work is performed in the framework of the Lead Project Porous Materials @ Work for Sustainability at TU Graz in cooperation with the Institute of Biotechnology and Biochemical Engineering.
References:
[1] L.M. Novak, E.-M. Steyskal, RSC Adv., 13 (2023) 6947-6953.
Michael Stadlhofer
Liquid helium nanodroplets, acting as nano-cryo reactors, offer a unique environment to study weakly bound molecular clusters using advanced ultrafast photoelectron and ion spectroscopy techniques. The droplets offer a controlled environment for studying photoinduced molecular processes, such as hydrogen transfer reactions. To understand these reactions fully, it is essential to monitor the geometry of molecular clusters both before and during the photoinduced reaction. Coulomb explosion imaging is a technique that can reveal interatomic distances by analyzing the velocities of ions after a Coulomb explosion, which occurs when a molecule is double ionized and breaks apart. However, Coulomb explosion imaging inside helium droplets is complex, because the ion velocities are influenced by the strong ion-helium interaction. This study focuses on applying Coulomb explosion imaging to iodine molecules I2 embedded within superfluid helium. The goal is to measure and model the kinetic energies of iodine ions produced during the explosion, as well as to understand how the liquid helium environment affects the movement of the ions. We aim to determine key parameters of the ion kinetics in the nanodroplets, such as ion-helium collision cross-sections and ion-droplet solvation energy, by comparing experimental data with helium density functional theory and molecular dynamics calculations. An accurate model for how the detected ion velocity distributions relate to the interatomic distance of the ground state iodine molecule will allow us to reconstruct the motion of atoms in the droplet after photoexcitation.
Sergei Gladyshev
In recent years, all-dielectric nanophotonics has emerged as a pivotal field in nano-optics. Serving as a promising alternative to plasmonics, dielectric nanoparticles exhibit the ability to sustain strong Mie resonances, which enhance light-matter interactions with minimal Ohmic losses. This advancement paves the way for achieving high efficiencies and exploring novel regimes of light manipulation. One intriguing phenomenon in this field is the transverse Kerker effect, where both forward and backward scattering are suppressed while lateral scattering is enhanced. However, complete suppression of forward scattering in passive structures is precluded by the optical theorem, rendering the realization of the transverse Kerker effect only approximate.
In this work, we reveal that a perfect transverse Kerker effect can indeed be achieved in passive structures by leveraging the concept of optical bound states in the continuum (BICs) — electromagnetic states that are spatially localized within photonic structures while coexisting with radiative modes. This phenomenon leads to the formation of exotic accidental BICs at the Γ point in a metasurface composed of dielectric nanocylinders, ultimately enabling complete suppression of scattering.
David Grafinger: Nano-Optics in Ultrafast Physics
Johanna Moser: Phsics-consistent machine learning for predictive maintenance of wind power plants
Greta Capello: CORHI-X: Investigating Heliospheric Events Through Multiple Observation Angles and Heliocentric Distances
Christoph Gruber: Supercontinuum Dual-Comb Spectroscopy
Deepak Bisht: From Molecules to Clouds: ML Insights into Cloud Condensation Nuclei Formation in Exoplanet Atmospheres
Elias Fösleitner: How accurate is the pole expansion of the scattering matrix?
Amaia Razquin Lizarraga: Coronal dimmings associated with the May 2024 flare/CME events from AR 13664
Florian Küstner: Photostrommessung auf QD Monolagen
Felix Hitzelhammer: Simulating non-classical light sources using stochastic processes coupled to FDTD
Alexander Grossek: Comparison of Ultrafast Pulse Characterisation Techniques
Sandipan Borthakur: Stellar Photospheric Contamination: Evolution from Protoplanetary to Debris Disks
Nidhi Bangera
Understanding exoplanet atmospheres is key to uncovering their formation histories, with the carbon-to-oxygen (C/O) ratio serving as a crucial tracer. In this work, we model the atmospheric chemistry of Hot-Jupiter WASP-69 b, using 1D photochemical-kinetic disequilibrium models. We explore how CH4 and C2H2, two key molecules detected in high-resolution transmission spectroscopy, respond to variations in mixing strength (Kzz), local gas temperature and C/O ratio. By comparing our model spectra to observations through cross-correlation analysis, we assess whether the C/O ratio can be constrained.
Vartika Pandey
Numerical models of the solar atmosphere are widely used in solar research and provide insights into unsolved problems such as the heating of coronal loops. A prerequisite for such simulations is an initial condition for the plasma temperature and density. Many explicit numerical schemes employ high-order derivatives that require some diffusion, for example, isotropic diffusion, for each independent
variable to maintain numerical stability. Otherwise, significant numerical inaccuracies and subsequent wiggles will occur and grow at steep temperature gradients in the solar transition region. We tested how to adapt the isotropic heat conduction to the grid resolution so that the model is capable of resolving varying temperature gradients. Our ultimate goal is to construct an atmospheric stratification that can serve as an initial condition for multi-dimensional models. Our temperature stratification spans from the solar interior
to the outer corona. From that, we computed the hydrostatic density stratification. Since numerical and analytical derivatives are not identical, the model needs to settle to a numerical equilibrium to fit all model parameters, such as mass diffusion and radiative losses. To compensate for energy losses in the corona, we implemented an artificial heating function that mimics the expected heat input from the 3D field-line braiding mechanism. Our heating function maintains and stabilises the obtained coronal temperature stratification. However, the diffusivity parameters need to be adapted to the grid spacing. Unexpectedly, we find that higher grid resolutions may need larger diffusivities contrary to the common understanding that high-resolution models are automatically more realistic and would need less
diffusivity. Smaller grid spacing causes larger temperature gradients in the solar transition region and hence a greater potential for numerical problems. We conclude that isotropic heat conduction is an efficient remedy when using explicit schemes with high-order numerical derivatives.
Tatiana Kormilina
For systems with complex morphology, 2D information can be insufficient, which requires tomographic approaches. Together, electron tomography, nanoscale and microscale X-ray CT cover the range from sub-nanometer resolution for small sample volumes, up to measuring macroscopical samples with micrometer precision, covering the majority of scales relevant in physical and life sciences. In the electron microscope this information can be coupled with analytical information from associated spectroscopy techniques. Analytical spectroscopic techniques such as electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS) are indispensable tools in materials science as they reveal elemental composition of the specimen and, in case of EELS, can point out the chemical bonding and electronic properties.
In this talk we will discuss the principles and challenges of tomography based on electron and x-ray imaging. We will take a close look at methodological advances, developed and implemented by the speaker on various levels from data acquisition to post-processing stages.
We will explore the power of correlating information from complementary techniques and mutually enhancing the data quality of multimodal datasets. The abovementioned will be illustrated on user cases of several diverse material systems spreading through different application fields and length scales, including:
i) investigating the degree and origin of critical laser damage in intraocular lenses;
ii) following the hierarchical structure of insect compound eye down to the cornea lens;
iii) classifying the composition of chondrules of Acfer094 meteorite;
iv) revealing the hidden interconnectivity of CuNiFe magnetic alloy precipitate phase;
v) finding 3D technique applicable to every stage of modifying nanoporous Copper materials for biocatalysis and quantifying pore parameters through scales.
Florian Brumbauer
Titanium alloys, especially Ti-6Al-4V, are widely used in clinical applications to substitute and stabilize bone structures such as tibial bones and hip joints. However, concerns have been raised regarding its long-term performance. In particular, their released ions when in contact with the challenging physiological environment of the human body as well as the V-rich oxides formed on their surface are considered toxic and their considerably higher Young`s modulus compared to bone leads to stress shielding effects that might result in bone atrophy and implant loosening. Well-designed β-Titanium alloys are excellent alternatives to alleviate these disadvantages. However, the formation of metastable phases in those β-Titanium alloys during manufacturing and/or heat treatments leads to embrittlement and often to a complete loss of ductility. Here, we propose an alloy design strategy aimed at preventing the embrittlement of those β-Titanium alloys. We were able to show, that additions of non-toxic Sn to β-Ti-12Cr alloys strongly suppresses the formation of these embrittling metastable phases through synergistic effects of the Cr and Sn atoms blocking the diffusion pathways necessary for the transformation to evolve. This inhibition of the elemental formation mechanism decisively widens the time-temperature process window by orders of magnitude, making them insensitive to cyclic-reheating during additive manufacturing (AM). However, biomechanical compatibility is only one of the challenging requirements to be fulfilled for biomaterials to be considered suitable for load-bearing applications. The corrosions resistance of the proposed alloys, their formed surface products and the metal ions released will strongly determine the cytocompatibility/useability of the biomaterials. We were able to show, that the Sn added β-Ti-12Cr alloys exhibits a superior long-term corrosion resistance compared to the clinically used Ti-6Al-4V with low passive dissolution rates especially around the reported body potential with amounts of released ions below the limit of detection.
Our proposed design strategy opens up huge opportunities for creating tailored biomedical implants adjusted to the patients needs, especially in context of the advancing additive manufacturing processes where the prevention of metastable phases during cyclic reheating still remains a severe obstacle.
[1] Brumbauer et al., Acta Mater., 262 (2024) 119466
[2] Okamoto, Brumbauer et al., Acta Mater., 273 (2024) 119968
Johannes Krondorfer
Nuclear electric resonance (NER) spectroscopy is currently experiencing a revival as a potential tool for quantum computing based on nuclear spins. Access to nuclear spin states via electric fields is provided by the nuclear quadrupole moment, a common feature of many standard isotopes, caused by the non-spherical shape of their nuclei.
Based on an in-depth analysis of the underlying coupling mechanism, we investigate the possibility of coherent spin control in atoms or molecules via nuclear quadrupole interaction from first principles. A general, time-dependent description is provided, which entails and reflects on commonly applied approximations often found in recent literature. We formulate and derive a corresponding effective spin Hamiltonian. This formalism is then used to propose a new method we refer to as `optical' nuclear electric resonance or `ONER'.
Our protocol takes advantage of time-modulated optical excitations via UV/visible light, e.g. realized by a pulsed laser, to control the electric field gradient at the position of a specific nucleus by periodic changes of the surrounding electron density. The proposed method is theoretically investigated for atomic and molecular benchmark systems. Based on ONER we propose a fast and robust single qubit gate for hyperfine qubits in trapped neutral atoms. Our findings suggest that it might be possible to shift complicated spin manipulation tasks in atomic, molecular or solid-state systems into the time domain by pulse-duration encoded laser signals.