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Organic semiconductors are a promising class of materials. Their special properties are the particularly good absorption, low weight and easy processing into thin films. Therefore, intense research has been devoted to the realization of thin film organic solar cells (OPVs). Because of the low dielectric constant of organic semiconductors, primary excitations (excitons) are strongly bound and a type II heterojunction needs to be introduced to split these excitations into free charges. Therefore, most organic solar cells consist of at least an electron donor and electron acceptor material. For such donor acceptor systems mainly three states are relevant; the photoexcited exciton on the donor or acceptor material, the charge transfer state at the donor-acceptor interface and the charge separated state of a free electron and hole. The interplay between these states significantly determines the efficiency of organic solar cells. Due to the high absorption and the low charge carrier mobilities, the active layers are usually thin but also, exciton dissociation and free charge formation proceeds rapidely, which makes the study of carrier dynamics highly challenging.
Therefore, the focus of this work was first to install new experimental setups for the investigation of the charge carrier dynamics in complete devices with superior sensitivity and time resolution and, second, to apply these methods to prototypical photovoltaic materials to address specific questions in the field of organic and hybrid photovoltaics.
Regarding the first goal, a new setup combining transient absorption spectroscopy (TAS) and time delayed collection field (TDCF) was designed and installed in Potsdam. An important part of this work concerned the improvement of the electronic components with respect to time resolution and sensitivity. To this end, a highly sensitive amplifier for driving and detecting the device response in TDCF was developed. This system was then applied to selected organic and hybrid model systems with a particular focus on the understanding of the loss mechanisms that limit the fill factor and short circuit current of organic solar cells.
The first model system was a hybrid photovoltaic material comprising inorganic quantum dots decorated with organic ligands. Measurements with TDCF revealed fast free carrier recombination, in part assisted by traps, while bias-assisted charge extraction measurements showed high mobility. The measured parameters then served as input for a successful description of the device performance with an analytical model.
With a further improvement of the instrumentation, a second topic was the detailed analysis of non-geminate recombination in a disordered polymer:fullerene blend where an important question was the effect of disorder on the carrier dynamics. The measurements revealed that early time highly mobile charges undergo fast non-geminate recombination at the contacts, causing an apparent field dependence of free charge generation in TDCF experiments if not conducted properly. On the other hand, recombination the later time scale was determined by dispersive recombination in the bulk of the active layer, showing the characteristics of carrier dynamics in an exponential density of state distribution. Importantly, the comparison with steady state recombination data suggested a very weak impact of non-thermalized carriers on the recombination properties of the solar cells under application relevant illumination conditions.
Finally, temperature and field dependent studies of free charge generation were performed on three donor-acceptor combinations, with two donor polymers of the same material family blended with two different fullerene acceptor molecules. These particular material combinations were chosen to analyze the influence of the energetic and morphology of the blend on the efficiency of charge generation. To this end, activation energies for photocurrent generation were accurately determined for a wide range of excitation energies. The results prove that the formation of free charge is via thermalized charge transfer states and does not involve hot exciton splitting. Surprisingly, activation energies were of the order of thermal energy at room temperature. This led to the important conclusion that organic solar cells perform well not because of predominate high energy pathways but because the thermalized CT states are weakly bound. In addition, a model is introduced to interconnect the dissociation efficiency of the charge transfer state with its recombination observable with photoluminescence, which rules out a previously proposed two-pool model for free charge formation and recombination. Finally, based on the results, proposals for the further development of organic solar cells are formulated.
Ferroic materials have attracted a lot of attention over the years due to their wide range of applications in sensors, actuators, and memory devices. Their technological applications originate from their unique properties such as ferroelectricity and piezoelectricity. In order to optimize these materials, it is necessary to understand the coupling between their nanoscale structure and transient response, which are related to the atomic structure of the unit cell.
In this thesis, synchrotron X-ray diffraction is used to investigate the structure of ferroelectric thin film capacitors during application of a periodic electric field. Combining electrical measurements with time-resolved X-ray diffraction on a working device allows for visualization of the interplay between charge flow and structural motion. This constitutes the core of this work. The first part of this thesis discusses the electrical and structural dynamics of a ferroelectric Pt/Pb(Zr0.2,Ti0.8)O3/SrRuO3 heterostructure during charging, discharging, and polarization reversal. After polarization reversal a non-linear piezoelectric response develops on a much longer time scale than the RC time constant of the device. The reversal process is inhomogeneous and induces a transient disordered domain state. The structural dynamics under sub-coercive field conditions show that this disordered domain state can be remanent and can be erased with an appropriate voltage pulse sequence. The frequency-dependent dynamic characterization of a Pb(Zr0.52,Ti0.48)O3 layer, at the morphotropic phase boundary, shows that at high frequency, the limited domain wall velocity causes a phase lag between the applied field and both the structural and electrical responses. An external modification of the RC time constant of the measurement delays the switching current and widens the electromechanical hysteresis loop while achieving a higher compressive piezoelectric strain within the crystal.
In the second part of this thesis, time-resolved reciprocal space maps of multiferroic BiFeO3 thin films were measured to identify the domain structure and investigate the development of an inhomogeneous piezoelectric response during the polarization reversal. The presence of 109° domains is evidenced by the splitting of the Bragg peak.
The last part of this work investigates the effect of an optically excited ultrafast strain or heat pulse propagating through a ferroelectric BaTiO3 layer, where we observed an additional current response due to the laser pulse excitation of the metallic bottom electrode of the heterostructure.
Membrane adhesion is a fundamental biological process in which membranes are attached to neighboring membranes or surfaces. Membrane adhesion emerges from a complex interplay between the binding of membrane-anchored receptors/ligands and the membrane properties. In this work, we study membrane adhesion mediated by lipid-anchored saccharides using microsecond-long full-atomistic molecular dynamics simulations. Motivated by neutron scattering experiments on membrane adhesion via lipid-anchored saccharides, we investigate the role of LeX, Lac1, and Lac2 saccharides and membrane fluctuations in membrane adhesion.
We study the binding of saccharides in three different systems: for saccharides in water, for saccharides anchored to essentially planar membranes at fixed separations, and for saccharides anchored to apposing fluctuating membranes. Our simulations of two saccharides in water indicate that the saccharides engage in weak interactions to form dimers. We find that the binding occurs in a continuum of bound states instead of a certain number of well-defined bound structures, which we term as "diffuse binding".
The binding of saccharides anchored to essentially planar membranes strongly depends on separation of the membranes, which is fixed in our simulation system. We show that the binding constants for trans-interactions of two lipid-anchored saccharides monotonically decrease with increasing separation. Saccharides anchored to the same membrane leaflet engage in cis-interactions with binding constants comparable to the trans-binding constants at the smallest membrane separations. The interplay of cis- and trans-binding can be investigated in simulation systems with many lipid-anchored saccharides. For Lac2, our simulation results indicate a positive cooperativity of trans- and cis-binding. In this cooperative binding the trans-binding constant is enhanced by the cis-interactions. For LeX, in contrast, we observe no cooperativity between trans- and cis-binding. In addition, we determine the forces generated by trans-binding of lipid-anchored saccharides in planar membranes from the binding-induced deviations of the lipid-anchors. We find that the forces acting on trans-bound saccharides increase with increasing membrane separation to values of the order of 10 pN.
The binding of saccharides anchored to the fluctuating membranes results from an interplay between the binding properties of the lipid-anchored saccharides and membrane fluctuations. Our simulations, which have the same average separation of the membranes as obtained from the neutron scattering experiments, yield a binding constant larger than in planar membranes with the same separation. This result demonstrates that membrane fluctuations play an important role at average membrane separations which are seemingly too large for effective binding. We further show that the probability distribution of the local separation can be well approximated by a Gaussian distribution. We calculate the relative membrane roughness and show that our results are in good agreement with the roughness values reported from the neutron scattering experiments.
In this work we investigated ultrafast demagnetization in a Heusler-alloy. This material belongs to the halfmetal and exists in a ferromagnetic phase. A special feature of investigated alloy is a structure of electronic bands. The last leads to the specific density of the states. Majority electrons form a metallic like structure while minority electrons form a gap near the Fermi-level, like in semiconductor. This particularity offers a good possibility to use this material as model-like structure and to make some proof of principles concerning demagnetization. Using pump-probe experiments we carried out time-resolved measurements to figure out the times of demagnetization. For the pumping we used ultrashort laser pulses with duration around 100 fs. Simultaneously we used two excitation regimes with two different wavelengths namely 400 nm and 1240 nm. Decreasing the energy of photons to the gap size of the minority electrons we explored the effect of the gap on the demagnetization dynamics. During this work we used for the first time OPA (Optical Parametrical Amplifier) for the generation of the laser irradiation in a long-wave regime. We tested it on the FETOSPEX-beamline in BASSYII electron storage ring. With this new technique we measured wavelength dependent demagnetization dynamics. We estimated that the demagnetization time is in a correlation with photon energy of the excitation pulse. Higher photon energy leads to the faster demagnetization in our material. We associate this result with the existence of the energy-gap for minority electrons and explained it with Elliot-Yaffet-scattering events. Additionally we applied new probe-method for magnetization state in this work and verified their effectivity. It is about the well-known XMCD (X-ray magnetic circular dichroism) which we adopted for the measurements in reflection geometry. Static experiments confirmed that the pure electronic dynamics can be separated from the magnetic one. We used photon energy fixed on the L3 of the corresponding elements with circular polarization. Appropriate incidence angel was estimated from static measurements. Using this probe method in dynamic measurements we explored electronic and magnetic dynamics in this alloy.
Movement and navigation are essential for many organisms during some parts of their lives. This is also true for bacteria, which can move along surfaces and swim though liquid environments. They are able to sense their environment, and move towards environmental cues in a directed fashion.
These abilities enable microbial lifecyles in biofilms, improved food uptake, host infection, and many more. In this thesis we study aspects of the swimming movement - or motility - of the soil bacterium (P. putida). Like most bacteria, P. putida swims by rotating its helical flagella, but their arrangement differs from the main model organism in bacterial motility research: (E. coli). P. putida is known for its intriguing motility strategy, where fast and slow episodes can occur after each other. Up until now, it was not known how these two speeds can be produced, and what advantages they might confer to this bacterium.
Normally the flagella, the main component of thrust generation in bacteria, are not observable by ordinary light microscopy. In order to elucidate this behavior, we therefore used a fluorescent staining technique on a mutant strain of this species to specifically label the flagella, while leaving the cell body only faintly stained. This allowed us to image the flagella of the swimming bacteria with high spacial and temporal resolution with a customized high speed fluorescence microscopy setup. Our observations show that P. putida can swim in three different modes. First, It can swim with the flagella pushing the cell body, which is the main mode of swimming motility previously known from other bacteria. Second, it can swim with the flagella pulling the cell body, which was thought not to be possible in situations with multiple flagella. Lastly, it can wrap its flagellar bundle around the cell body, which results in a speed wich is slower by a factor of two. In this mode, the flagella are in a different physical conformation with a larger radius so the cell body can fit inside. These three swimming modes explain the previous observation of two speeds, as well as the non strict alternation of the different speeds.
Because most bacterial swimming in nature does not occur in smoothly walled glass enclosures under a microscope, we used an artificial, microfluidic, structured system of obstacles to study the motion of our model organism in a structured environment. Bacteria were observed in microchannels with cylindrical obstacles of different sizes and with different distances with video microscopy and cell tracking. We analyzed turning angles, run times, and run length, which we compared to a minimal model for movement in structured geometries. Our findings show that hydrodynamic interactions with the walls lead to a guiding of the bacteria along obstacles. When comparing the observed behavior with the statics of a particle that is deflected with every obstacle contact, we find that cells run for longer distances than that model.
Navigation in chemical gradients is one of the main applications of motility in bacteria. We studied the swimming response of P. putida cells to chemical stimuli (chemotaxis) of the common food preservative sodium benzoate. Using a microfluidic gradient generation device, we created gradients of varying strength, and observed the motion of cells with a video microscope and subsequent cell tracking. Analysis of different motility parameters like run lengths and times, shows that P. putida employs the classical chemotaxis strategy of E. coli: runs up the gradient are biased to be longer than those down the gradient. Using the two different run speeds we observed due to the different swimming modes, we classify runs into `fast' and `slow' modes with a Gaussian mixture model (GMM). We find no evidence that P. putida's uses its swimming modes to perform chemotaxis.
In most studies of bacterial motility, cell tracking is used to gather trajectories of individual swimming cells. These trajectories then have to be decomposed into run sections and tumble sections. Several algorithms have been developed to this end, but most require manual tuning of a number of parameters, or extensive measurements with chemotaxis mutant strains. Together with our collaborators, we developed a novel motility analysis scheme, based on generalized Kramers-Moyal-coefficients. From the underlying stochastic model, many parameters like run length etc., can be inferred by an optimization procedure without the need for explicit run and tumble classification. The method can, however, be extended to a fully fledged tumble classifier. Using this method, we analyze E. coli chemotaxis measurements in an aspartate analog, and find evidence for a chemotactic bias in the tumble angles.
Force plays a fundamental role in the regulation of biological processes. Cells can sense the mechanical properties of the extracellular matrix (ECM) by applying forces and transmitting mechanical signals. They further use mechanical information for regulating a wide range of cellular functions, including adhesion, migration, proliferation, as well as differentiation and apoptosis. Even though it is well understood that mechanical signals play a crucial role in directing cell fate, surprisingly little is known about the range of forces that define cell-ECM interactions at the molecular level.
Recently, synthetic molecular force sensor (MFS) designs have been established for measuring the molecular forces acting at the cell-ECM interface. MFSs detect the traction forces generated by cells and convert this mechanical input into an optical readout. They are composed of calibrated mechanoresponsive building blocks and are usually equipped with a fluorescence reporter system. Up to date, many different MFS designs have been introduced and successfully used for measuring forces involved in the adhesion of mammalian cells. These MFSs utilize different molecular building blocks, such as double-stranded deoxyribonucleic acid (dsDNA) molecules, DNA hairpins and synthetic polymers like polyethylene glycol (PEG). These currently available MFS designs lack ECM mimicking properties.
In this work, I introduce a new MFS building block for cell biology applications, derived from the natural ECM. It combines mechanical tunability with the ability to mimic the native cellular microenvironment. Inspired by structural ECM proteins with load bearing function, this new MFS design utilizes coiled coil (CC)-forming peptides. CCs are involved in structural and mechanical tasks in the cellular microenvironment and many of the key protein components of the cytoskeleton and the ECM contain CC structures. The well-known folding motif of CC structures, an easy synthesis via solid phase methods and the many roles CCs play in biological processes have inspired studies to use CCs as tunable model systems for protein design and assembly. All these properties make CCs ideal candidates as building blocks for MFSs. In this work, a series of heterodimeric CCs were designed, characterized and further used as molecular building blocks for establishing a novel, next-generation MFS prototype.
A mechanistic molecular understanding of their structural response to mechanical load is essential for revealing the sequence-structure-mechanics relationships of CCs. Here, synthetic heterodimeric CCs of different length were loaded in shear geometry and their mechanical response was investigated using a combination of atomic force microscope (AFM)-based single-molecule force spectroscopy (SMFS) and steered molecular dynamics (SMD) simulations. SMFS showed that the rupture forces of short heterodimeric CCs (3-5 heptads) lie in the range of 20-50 pN, depending on CC length, pulling geometry and the applied loading rate (dF/dt). Upon shearing, an initial rise in the force, followed by a force plateau and ultimately strand separation was observed in SMD simulations. A detailed structural analysis revealed that CC response to shear load depends on the loading rate and involves helix uncoiling, uncoiling-assisted sliding in the direction of the applied force and uncoiling-assisted dissociation perpendicular to the force axis.
The application potential of these mechanically characterized CCs as building blocks for MFSs has been tested in 2D cell culture applications with the goal of determining the threshold force for cell adhesion. Fully calibrated, 4- to 5-heptad long, CC motifs (CC-A4B4 and CC-A5B5) were used for functionalizing glass surfaces with MFSs. 3T3 fibroblasts and endothelial cells carrying mutations in a signaling pathway linked to cell adhesion and mechanotransduction processes were used as model systems for time-dependent adhesion experiments. A5B5-MFS efficiently supported cell attachment to the functionalized surfaces for both cell types, while A4B4-MFS failed to maintain attachment of 3T3 fibroblasts after the first 2 hours of initial cell adhesion. This difference in cell adhesion behavior demonstrates that the magnitude of cell-ECM forces varies depending on the cell type and further supports the application potential of CCs as mechanoresponsive and tunable molecular building blocks for the development of next-generation protein-based MFSs.This novel CC-based MFS design is expected to provide a powerful new tool for observing cellular mechanosensing processes at the molecular level and to deliver new insights into the mechanisms and forces involved. This MFS design, utilizing mechanically tunable CC building blocks, will not only allow for measuring the molecular forces acting at the cell-ECM interface, but also yield a new platform for the development of mechanically controlled materials for a large number of biological and medical applications.
A reliable inference of networks from data is of key interest in many scientific fields. Several methods have been suggested in the literature to reliably determine links in a network. These techniques rely on statistical methods, typically controlling the number of false positive links, but not considering false negative links. In this thesis new methodologies to improve network inference are suggested. Initial analyses demonstrate the impact of falsepositive and false negative conclusions about the presence or absence of links on the resulting inferred network. Consequently, revealing the importance of making well-considered choices leads to suggest new approaches to enhance existing network reconstruction methods.
A simulation study, presented in Chapter 3, shows that different values to balance false positive and false negative conclusions about links should be used in order to reliably estimate network characteristics. The existence of type I and type II errors in the reconstructed network, also called biased network, is accepted. Consequently, an analytic method that describes the influence of these two errors on the network structure is explored. As a result of this analysis, an analytic formula of the density of the biased vertex degree distribution is found (Chapter 4).
In the inverse problem, the vertex degree distribution of the true underlying network is analytically reconstructed, assuming the probabilities of type I and type II errors. Chapters 4-5 show that the method is robust to incorrect estimates of α and β within reasonable limits. In Chapter 6, an iterative procedure to enhance this method is presented in the case of large errors on the estimates of α and β.
The investigations presented so far focus on the influence of false positive and false negative links on the network characteristics. In Chapter 7, the analysis is reversed - the study focuses on the influence of network characteristics on the probability of type I and type II errors, in the case of networks of coupled oscillators. The probabilities of α and β are influenced by the shortest path length and the detour degree, respectively. These results have been used to improve the network reconstruction, when the true underlying network is not known a priori, introducing a novel and advanced concept of threshold.
Advancing charge selective contacts for efficient monolithic perovskite-silicon tandem solar cells
(2019)
Hybrid organic-inorganic perovskites are one of the most promising material classes for photovoltaic energy conversion. In solar cells, the perovskite absorber is sandwiched between n- and p-type contact layers which selectively transport electrons and holes to the cell’s cathode and anode, respectively. This thesis aims to advance contact layers in perovskite solar cells and unravel the impact of interface and contact properties on the device performance. Further, the contact materials are applied in monolithic perovskite-silicon heterojunction (SHJ) tandem solar cells, which can overcome the single junction efficiency limits and attract increasing attention. Therefore, all contact layers must be highly transparent to foster light harvesting in the tandem solar cell design. Besides, the SHJ device restricts processing temperatures for the selective contacts to below 200°C.
A comparative study of various electron selective contact materials, all processed below 180°C, in n-i-p type perovskite solar cells highlights that selective contacts and their interfaces to the absorber govern the overall device performance. Combining fullerenes and metal-oxides in a TiO2/PC60BM (phenyl-C60-butyric acid methyl ester) double-layer contact allows to merge good charge extraction with minimized interface recombination. The layer sequence thereby achieved high stabilized solar cell performances up to 18.0% and negligible current-voltage hysteresis, an otherwise pronounced phenomenon in this device design. Double-layer structures are therefore emphasized as a general concept to establish efficient and highly selective contacts.
Based on this success, the concept to combine desired properties of different materials is transferred to the p-type contact. Here, a mixture of the small molecule Spiro-OMeTAD [2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluoren] and the doped polymer PEDOT [poly(3,4-ethylenedioxythiophene)] is presented as a novel hole selective contact. PEDOT thereby remarkably suppresses charge recombination at the perovskite surface, allowing an increase of quasi-Fermi level splitting in the absorber. Further, the addition of Spiro-OMeTAD into the PEDOT layer is shown to enhance charge extraction at the interface and allow high efficiencies up to 16.8%.
Finally, the knowledge on contact properties is applied to monolithic perovskite-SHJ tandem solar cells. The main goal is to optimize the top contact stack of doped Spiro-OMeTAD/molybdenum oxide(MoOx)/ITO towards higher transparency by two different routes. First, fine-tuning of the ITO deposition to mitigate chemical reduction of MoOx and increase the transmittance of MoOx/ITO stacks by 25%. Second, replacing Spiro-OMeTAD with the alternative hole transport materials PEDOT/Spiro-OMeTAD mixtures, CuSCN or PTAA [poly(triaryl amine)]. Experimental results determine layer thickness constrains and validate optical simulations, which subsequently allow to realistically estimate the respective tandem device performances. As a result, PTAA represents the most promising replacement for Spiro-OMeTAD, with a projected increase of the optimum tandem device efficiency for the herein used architecture by 2.9% relative to 26.5% absolute. The results also reveal general guidelines for further performance gains of the technology.
The unceasing impact of intense sunlight on earth constitutes a continuous source of energy fueling countless natural processes. On a molecular level, the energy contained in the electromagnetic radiation is transferred through photochemical processes into chemical or thermal energy. In the course of such processes, photo-excitations promote molecules into thermally inaccessible excited states. This induces adaptations of their molecular geometry according to the properties of the excited state. Decay processes towards energetically lower lying states in transient molecular geometries result in the formation of excited state relaxation pathways. The photo-chemical relaxation mechanisms depend on the studied system itself, the interactions with its chemical environment and the character of the involved states. This thesis focuses on systems in which photo-induced deprotonation processes occur at specific atomic sites.
To detect these excited-state proton dynamics at the affected atoms, a local probe of molecular electronic structure is required. Therefore, site-selective and orbital-specific K-edge soft X-ray spectroscopy techniques are used here to detect photo-induced proton dynamics in gaseous and liquid sample environments. The protonation of nitrogen (N) sites in organic molecules and the oxygen (O) atom in the water molecule are probed locally through transitions between 1s orbitals and the p-derived molecular valence electronic structure. The used techniques are X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Both yield access to the unoccupied local valence electronic structure, whereas the latter additionally probes occupied states.
We apply these probes in optical pump X-ray probe experiments to investigate valence excited-state proton transfer capabilities of aqueous 2-thiopyridone. A characteristic shift of N K-edge X-ray absorption resonances as well as a distinct X-ray emission line are established by us as spectral fingerprints of N deprotonation in the system. We utilize them to identify photo-induced N deprotonation of 2-thiopyridone on femtosecond timescales, in optical pump N K-edge RIXS probe measurements. We further establish excited state proton transfer mechanisms on picosecond and nanosecond timescales along the dominant relaxation pathways of 2-thiopyridone using transient N K-edge XAS.
Despite being an excellent probe mechanism for valence excited-state proton dynamics, the K-edge core-excitation itself also disturbs the electronic structure at specific sites of a molecule. The rapid reaction of protons to 1s photo-excitations can yield directional structural distortions within the femtosecond core-excited state lifetime. These directional proton dynamics can change the energetic separation of eigenstates of the system and alter probabilities for radiative decay between them. Both effects yield spectral signatures of the dynamics in RIXS spectra.
Using these signatures of RIXS transitions into electronically excited states, we investigate proton dynamics induced by N K-edge excitation in the amino-acid histidine. The minor core-excited state dynamics of histidine in basic and neutral chemical environments allow us to establish XAS and RIXS spectral signatures of different N protonation states at its imidazole N sites. Based on these signatures, we identify an excitation-site-independent N-H dissociation for N K-edge excitation under acidic conditions.
Such directional structural deformations, induced by core-excitations, also make proton dynamics in electronic ground states accessible through RIXS transitions into vibrationally excited states. In that context, we interpret high resolution RIXS spectra of the water molecule for three O K-edge resonances based on quantum-chemical wave packet propagation simulations. We show that highly oriented ground state vibrational modes of coupled nuclear motion can be populated through RIXS processes by preparation of core-excited state nuclear wave packets with the same directionality. Based on that, we analytically derive the possibility to extract one-dimensional directional cuts through potential energy surfaces of molecular systems from the corresponding RIXS spectra. We further verify this concept through the extraction of the gas-phase water ground state potential along three coordinates from experimental data in comparison to quantum-chemical simulations of the potential energy surface.
This thesis also contains contributions to instrumentation development for investigations of photo-induced molecular dynamics at high brilliance X-ray light sources. We characterize the setup used for the transient valence-excited state XAS measurements of 2-thiopyridone. Therein, a sub-micrometer thin liquid sample environment is established employing in-vacuum flat-jet technology, which enables a transmission experimental geometry. In combination with a MHz-laser system, we achieve a high detection sensitivity for photo-induced X-ray absorption changes. Additionally, we present conceptual improvements for temporal X-ray optical cross-correlation techniques based on transient changes of multilayer optical properties, which are crucial for the realization of femtosecond time-resolved studies at synchrotrons and free-electron lasers.
Samarium hexaboride
(2018)