Robert Schwarzl
Within the field of organic semiconductors, squaraines stand out due to their high molar absorption in the visible and near infrared regions. Strongly zwitterionic ground and excited states result in a pronounced structure-function relationship from intermolecular coupling. This enables us to tune optical absorption spectra and their transition dipole moment, altering the geometry by modifying otherwise passive chemical moieties and by changing sample preparation conditions. The range of samples covered in this PhD thesis spans from dilute, colloidal solutions, dispersed monomers in amorphous matrices to multiple forms of beautiful molecular crystals. One particular form, SQIB Pbcn, is among the few materials showing triplet Davydov splitting, a lifting of degeneracy from a single absorption peak in a monomer to three perpendicularly oriented absorption peaks in a Z=4 molecular crystal.
In terms of measurement techniques, I used femtosecond lasers in a pump-probe spectroscopy scheme called transient absorption. This comparatively simple pump-probe concept is used to fulfill different requirements like spatial resolution using microscope objectives, few-cycle temporal resolution using gas-filled hollow core fibers and pulse compression, and orientational resolution by implementing transient reflectivity in an ellipsometry layout. Combined with essential input from our theoretical and experimental collaborators, this talk combines experimental characterization of higher excited states and excited state lifetimes beyond the reach of conventional spectroscopy with semi-empirical and ab-initio theoretical models to simulate the nature of the excited states involved.
Robert di Vora
Utilizing frequency comb laser systems, spectroscopy experiments that probe phenomena across an extraordinary span of timescales are enabled. At the slow end, scanning tunneling microscopy (STM) combined with lasers allows detailed investigation of metastable molecular isomerization, where states persist long enough for molecular-scale characterization based on computer vision (CV) methods. At the opposite extreme, ultrafast UV interferometry captures dynamics unfolding on femtosecond timescales, revealing processes lasting less than 100 fs. This talk traces a continuous journey through these temporal regimes, highlighting how a unified laser platform bridges measurements from minutes to femtoseconds and unlocks insights into molecular structure and dynamics across the time domain.
Anthony Moulin: Tracing Magnetic Helicity from the Solar Source Region to Interplanetary Space
Florian Kröll: Understanding signatures of stellar activity in Extreme Precision Radial Velocity data
Markus Baumgartner-Steinleitner: Structure of the large Scale Coronal Wave observed on 06th September 2011
Christoph Stockinger: Detecting light with passive waveguide architectures
Lukas Lobenwein: Evaluating the limits of EELS and DPC for qualitative and quantitative analysis of trace elements in WBG semiconductors – ELEVATE
Florian Zrim: Influence of the microstructure on the ductility of aluminium alloys
Diana Shakirova
In this study, we explore how the interaction between two quasi-bound states in the continuum (quasi-BICs), i.e., high-quality-factor resonant states, can boost molecular chiroptical response. For the first time, we derive a strict recipe to maximize the crosstalk of quasi-BICs of a nanophotonic resonator to enhance the molecular differential transmittance as well as we provide a metasurface design that allows us to realize the effect in the visible frequency range. The suggested structure is optimized according to fabrication restrictions and paves the way toward ultrasensitive detection of chiral molecules by driving the chiroptical response into experimentally detectable level. The latter is confirmed by the modal theory and numerical simulations being in excellent agreement.
Masoud Hamidi
We introduce a quasi-Babinet principle for dielectric systems that connects dielectric Mie voids with their complementary high-index resonators. This principle relates their resonant properties and enables straightforward design rules for building resonators with advanced functionalities. Inspired by the classical Babinet’s principle for metallic apertures, our generalization applies to dielectric and magnetodielectric systems. For spherical geometries, we establish an analytic form that links the electric and magnetic fields, as well as resonant frequencies and quality factors, of complementary structures. This principle provides new physical insight and practical tools for engineering dielectric resonators, with potential applications in nanophotonics, sensing, and quantum information.
Siegfried Kaidisch
Photoemission orbital tomography (POT) is a combined experimental and theoretical technique that provides an intuitive understanding of angle-resolved photoemission spectroscopy (ARPES) in terms of electronic orbitals. The theoretical framework was recently extended to describe photoemission from excited states of gas-phase molecular systems (Kern, Phys. Rev. B 108, 085132, 2023), enabling theoretical insights into pump-probe ARPES experiments.
In this contribution, we present a further development toward photoemission from optically excited states in periodic systems. We derive a formula that allows for the computation of photoemission angular distributions based on GW/BSE results, discuss the approximations involved, and provide technical details of our implementation. Finally, we demonstrate the capabilities of our approach on the example of an organic molecular layer and compare our predictions to corresponding time-resolved ARPES experiments.
Michelle Brugger-Hatzl
Correlating different microscopy techniques is of growing interest across various research fields, as it enables the combination of complementary strengths to provide more comprehensive insights into material’s properties. However, differences in sample preparation requirements and the need to transfer specimens between instruments can make it challenging to examine/analyse the same region of interest with multiple methods. For example, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) are highly complementary methods. While TEM provides atomic- and nanoscale structural and chemical information, AFM offers 3D surface topography, mechanical, electrostatic and magnetic information. Direct correlation between the two, however, is often hindered by the strict sample requirement for TEM of electron transparency, which typically limits sample thickness to below 100 nm. This study explores the feasibility of correlating AFM with TEM without modifying standard TEM sample preparation protocols. AFM measurements were performed on conventional TEM sample types, addressing challenges such as sample oscillation, mechanical stability and limited surface accessibility. The study presents both limitations and successful strategies, demonstrating that AFM can indeed be applied to TEM samples without additional preparation steps, thus paving the way for integrated correlative workflows between these instruments.
Fabian Gasser
Grazing incidence X-ray diffraction (GIXD) is widely used for the structural characterization of thin film, particularly for analysing the phase composition and orientation distribution of crystallites. While qualitative evaluation tools are well established, a widely applicable and systematic procedure for extracting quantitative information has not yet been developed. As a first step towards such a methodology, an approach that enables accurate quantitative analysis through the evaluation of radial line profiles extracted from GIXD measurements is presented here. To ensure reliability of the extracted intensities, correction factors were derived for state-of-the-art GIXD setups and validated on measured data of model systems. Building on this foundation, quantitative analysis of measured GIXD data was performed for a variety of sample. An algorithm was developed to compute radial line profiles based on known crystals structures. By fitting the calculated line profiles to the experimental data extracted from GIXD measurements, precise quantitative information on orientation distribution and phase composition was obtained, along with additional parameters such as mosaicity and total crystal volume. This work provides a systematic and broadly applicable framework for extracting quantitative information from GIXD data. Moreover, the derived intensity correction factors offer improved crystal structure solutions from thin films.
Raphael Hauer
We present B-PHAT, a new method for measuring the size and number concentration of microparticles
in a time-resolved manner. Building on the microfluidic infrastructure of the proprietary OF2i® technology [1], B-PHAT combines incoherent illumination with continuous sample flow and imaging optics. Its core innovation lies in moving the carrier liquid through the optic’s focal plane, thereby ensuring that every particle above the detection threshold will inevitably be sharply imaged as it passes through focus. A dedicated evaluation software automatically processes the video by background subtraction, particle detection and tracking, and selecting the sharpest image for size determination. Particle concentrations are derived directly from the sample flow rate, measurement time, and particle count. This approach allows robust analysis of a wide range of particle sizes and shapes without extensive calibration. B-PHAT is simple, cost-effective, and intuitive. It provides size- and time-resolved particle data and offers a versatile tool for applications where both particle size and concentration dynamics are of interest. Its capabilities are demonstrated in the figure below.
[1] M. Šimić et al., Phys. Rev. Appl. 18, 024056 (2022); ibid. 19, 034041 (2023).
Amaia Razquin Lizarraga
Coronal dimmings are regions of transiently reduced brightness in extreme ultraviolet (EUV) and soft X-ray (SXR) images of the Sun. They are interpreted as the decrease of coronal density and plasma evacuation caused by the onset of coronal mass ejections (CMEs), thus coronal dimmings serve as powerful diagnostics of CME initiation and early evolution. CMEs are large structures of magnetised plasma expelled from the Sun into the heliosphere. Solar CMEs are the main cause of space weather disturbances in Earth's atmosphere and magnetosphere. The development of diagnostic tools for coronal dimmings can yield additional information regarding CMEs, which can in turn be used for the detection of Earth-directed CMEs and stellar CMEs.
In this study, we analyse the coronal dimmings linked to the intense flare and CME activity from active region (AR) 13664 during May 2024. AR 13664 was among the most flare-productive regions in recent decades, generating 55 M-class and 12 X-class flares along with multiple Earth-directed CMEs. The rapid succession of these CMEs triggered the most intense geomagnetic storm in two decades. We study coronal dimmings from a single active region (AR 13664) using data from the Solar Dynamics Observatory (SDO). We find 16 on-disc coronal dimming events and investigate how their characteristic parameters -- such as area, brightness and magnetic flux -- relate to key flare and CME properties. We also examine the spatial relationship between dimmings and flare ribbons, as well as overarching magnetic structures.
In this single-AR study we find enhanced correlations between dimming parameters and flare strength compared to broader statistical samples. We also find a systematic shift in the dimming morphology over time, linked to shifting sites of magnetic reconnection. In some cases, dimmings reveal trans-hemispheric connections driven by localised reconnection. These findings highlight the importance of dimming observations and underscore their value in understanding and forecasting CME behaviour.
Michael Sieberer
This work introduces CRYDAC, a cryogenically compatible microchip designed to generate ultra stable, low noise voltages for controlling ion traps, key building blocks of future quantum computers. By operating reliably at temperatures as low as 13 K and sitting in close proximity to the trapped ions, CRYDAC overcomes the wiring bottlenecks that would otherwise limit large scale quantum systems. The design combines advanced digital to analog conversion, integrated filtering, and noise cancellation techniques to deliver precise signals without external components, all while consuming minimal power. Beyond enabling more compact and scalable ion trap architectures, CRYDAC demonstrates how tailored circuit strategies can preserve performance in extreme cryogenic environments, paving the way for practical, high fidelity quantum control hardware.
Simon Hollweger
Adsorbed organic molecules on crystalline surfaces can form a variety of different surface polymorphs with potentially significant differences in their physical properties. Which structure on the surface is the energetically favored one at a given temperature and pressure is given by thermodynamics. However, due to kinetic effects during growth also metastable structures can form. In this theses we investigate an mechanism with which the formation of a metastable surface structure is achieved. With targeted temperature and pressure changes in the system a controlled rearrangement of the adsorbed molecules is triggered and a metastable polymorph forms on the surface. To show the validity of the proposed mechanism we perform Kinetic Monte Carlo growth simulations of hypothetical organic molecules adsorbing on a crystalline surface. These simulations show that it is possible to form a metastable structure simply with external temperature and pressure changes.
Additionally we use the kinetic Monte Carlo results to optimize the required temperature and pressure curves with Optimal Control Theory to minimize the required time to achieve a maximal yield.
Dominik Brandstetter
Metal-organic frameworks (MOFs) are composed metal centres connected by linker molecules and have been a hot topic in solid state physics for some time now. Recently, also their two-dimensional counter parts have drawn significant attention as a new class of versatile materials. Arguably one of their biggest benefits over other conventional 2D materials such as graphene is the potential tunability of their electronic and magnetic properties. By strategically choosing the constituents and careful controlling the synthesis parameters, the electronic structure can be manipulated in a controlled way. However, this requires substantial knowledge about the band formation in the network. Recent investigations have shown indications for a metal-organic hybrid band structure as well as intricate charge transfer characteristics and magnetic properties in 2D MOFs. Nevertheless, a fundamental understanding of the nature of the chemical bond between the organic ligands and the transition metal atoms is still lacking. In my submission I will present our recent investigations into the nature of this metal-molecular coordination bond by a combination of density functional calculations with angle-resolved photoemission experiments in the joined framework of photoemission orbital tomography.
[1] M. Ko et al., Chem. Comm. 54, (2018)
[2] D. Baranowski et al. ACS Nano 18, 30 (2024)
[3] S. Mearini et al., Adv. Science 11, 38 (2024)
Florian Lindner
Metal-organic frameworks (MOFs), with their open-framework architectures and tuneable building units, exhibit mechanical and thermal behaviours that diverge significantly from those of conventional inorganic materials. Throughout my PhD, I investigated these properties using a tightly integrated combination of experimental techniques and atomistic simulations. On the mechanical side, I employed Brillouin light scattering (BLS), a non-invasive optical method, to probe direction-dependent sound velocities in single MOF crystals, see Figure 1. By determining elastic tensor elements of a prototypical MOF through a tight integration of BLS measurements with density functional theory (DFT) and machine-learned interatomic potentials (MLIPs), we demonstrated the strong potential of this approach to reliably quantify anisotropic mechanical responses in MOFs. In parallel, I conducted extensive simulations of thermal transport properties, with a focus on lattice thermal conductivity. Both the Boltzmann Transport Equation (BTE) and equilibrium molecular dynamics based on Green-Kubo (GK) theory were employed to capture the low thermal conductivity characteristic of MOFs. This thermal transport modelling was carried out alongside my experimental efforts, forming a complementary picture of phonon behaviour across multiple length and time scales. As a future direction, I aim to explore the potential of the Green-Kubo formalism to compute shear viscosity, which would offer a promising route to connect thermal transport and mechanical dynamics in MOFs within a unified simulation framework.
Together, this work advances the understanding of structure–property relationships in MOFs and provides tools for tailoring their mechanical and thermal performance in application-relevant contexts.