|Jeremy Richardson, ETHZ
|Improvements in the simulation of nonadiabatic quantum dynamics
In the group of Prof. Richardson in ETH we are interested in mapping techniques, aimed at recasting hard quantum-mechanical problems onto classical systems which can be studied via computational methods. My postdoctoral project focuses on the development and test of mapping approaches to tackle the dynamics of electronic systems coupled to a condensed-phase nuclear environment. I am currently working on the development of a method suited to calculate nonadiabatic correlation functions in thermal equilibrium. Also, I am studying out-of-equilibrium nonadiabatic dynamics via the non-Markovian Mori-Nakajima-Zwanzig formalism.
|Jean-Pierre Wolf, UniGE
|High repetition rates investigation on energy deposition in air
The project aims at understanding the role of hydrodynamics in laser filamentation and its use for specific applications. Recent development in laser technology allowed both high peak powers and high average powers allowing this new paradigm of an interplay between hydrodynamics, Kerr effects and plasma generation. We will investigate energy deposition in air, through filamentation and rotational heating, for guiding high-voltage discharges over long distances. To achieve this goal several series of experiments will be conducted with a laser source at 1 kHz repetition rate and higher.
|Steve Johnson, ETHZ
|Ultrafast 2D spectroscopy of Weyl semimetals with intense terahertz light
The project aims at investigating the nonlinear ultrafast dynamics in crystalline materials with exotic electronic properties at a picosecond timescale, using the technique of two-dimensional Terahertz time domain spectroscopy. This experimental approach allows probing the electronic band structure, the coupling between different degrees of freedom (electrons, phonons, etc) and the nonlinear effects induced by intense THz electric fields. The project also encompasses the development of a computational platform for the efficient simulation of the nonlinear dynamics of carrier transport, useful for describing more conventional low-bandgap semiconductors as well as novel quantum materials.
|Jürg Osterwalder, UZH
|Photoinduced charge transfer dynamics at h-BN covered Cu and Cu2O surfaces
Cuprous oxide (Cu2O) is a promising photocathode for the hydrogen evolution reaction due to its large bandgap and cheap cost. To increase the corrosion resistance of Cu2O cathodes under photoelectrochemical cell conditions, hexagonal boron nitride (h-BN) can be deposited on the surface. Due to weak interactions between h-BN and Cu2O, confined reactions can occur underneath h-BN and be potentially enhanced by the nano-confinement effect. We have synthesized a h-BN/Cu2O heterostructure via intercalation and oxidation of h-BN/Cu(111) and are investigating the system structure using photoemission spectroscopy and diffraction, x-ray absorption, and scanning tunneling microscopy. Further characterization of the electron dynamics upon photoexcitation using time-resolved two-photon photoemission is underway. The goal is to obtain a molecular-level understanding of interactions within the h-BN/Cu2O/Cu(111) model catalyst system.
|1. Beckord J, Diulus JT, Novotny Z, Osterwalder J, Hengsberger M. 2023. Protected ultrathin cuprous oxide film for photocatalysis: Excitation and relaxation dynamics. Phys. Rev. Mater. 7: 045801 (https://link.aps.org/doi/10.1103/PhysRevMaterials.7.045801)
2. Boucly A, Artiglia L, Fabbri E, Palagin D, Aegerter D, Pergolesi D, Novotny Z, Comini N, Diulus JT, Huthwelker T, Ammann M, Schmidt TJ. 2022. Direct evidence of cobalt oxyhydroxide formation on a La0.2Sr0.8CoO3 perovskite water splitting catalyst. J. Mater. Chem. A 10: 2434-44 (https://doi.org/10.1039/D1TA04957G)
3. Brandalise Nunes F, Comini N, Diulus JT, Huthwelker T, Iannuzzi M, Osterwalder J, Novotny Z. 2023. Dynamic Equilibrium at the HCOOH-Saturated TiO2(110)–Water Interface. J. Phys. Chem. Lett. 14: 3132-8 (https://doi.org/10.1021/acs.jpclett.2c03788)
4. Comini N, Diulus JT, Parkinson GS, Osterwalder J, Novotny Z. 2023. Stability of Iridium Single Atoms on Fe3O4(001) in the mbar Pressure Range. J. Phys. Chem. C 127: 19097–106 (https://pubs.acs.org/doi/full/10.1021/acs.jpcc.3c03097)
5. Diulus JT, Tobler B, Osterwalder J, Novotny Z. 2021. Thermal oxidation of Ru(0001) to RuO2(110) studied with ambient pressure x-ray photoelectron spectroscopy. J. Phys. D: Appl. Phys. 54: 244001 (http://dx.doi.org/10.1088/1361-6463/abedfd)
6. Nunes FB, Comini N, Diulus JT, Huthwelker T, Iannuzzi M, Osterwalder J, Novotny Z. 2023. Dynamic Equilibrium at the HCOOH-Saturated TiO2(110)-Water Interface. J. Phys. Chem. Lett.: 3132-8 (https://pubs.acs.org/doi/10.1021/acs.jpclett.2c03788)
|Peter Hamm, UZH
|Single Shot two-dimensional Raman Terahertz Spectroscopy of Ionic Liquids
Single-shot terahertz detection will be combined with two-dimensional Raman-terahertz spectroscopy for the direct observation of transiently formed local structures of various solvents. The novel 2D Raman-terahertz setup will reduce the data acquisition time from many days to a few hours. Moreover, the combination of finely made echelons, high repetition rate laser, fast scanning and 100 kHz camera is expected to improve the signal-to-noise significantly. After implementing and optimising the setup, the new challenge would be to study the microscopic structure of various solvents, particularly hydrogen-bonded ionic liquids, for direct observation of the heterogeneity of their local network.
|Majed Chergui, EPFL
|Investigation on electronic structure and reactivity in heterometallic proteins
Enzymes with bimetallic carboxylate cofactors are ubiquitous in nature and catalyze numerous essential reactions.1 These cofactors are often found to be homometallic; however, in recent years the existence of bimetallic cofactors with heterometal active sites was established. The di-iron site in ribonucleotide reductase (RNRs) catalyzes essential steps in DNA synthesis. Unlike most RNRs, type R2lox2 contains an FeMn heterometallic cofactor. This enzyme has shown to perform different redox chemistry than the rest of RNRs, and is also capable of performing an unusually efficient photodecarboxylation3 upon irradiation. This photoactivity is rare in natural enzymes that do not facilitate photosynthesis making R2lox an interesting example of evolutionary optimization of photochemistry.
These observations lead one to question how the MnFe cofactors tune the reactivity in these enzymes. Specifically, what is the identity of the metal in the MLCT that triggers the photodecarboxylation3 and which are the first steps involved in this mechanism? These questions have been addressed by utilizing a probe of both the Mn and Fe with sensitivity to subtle changes in electronic structure. Both Fe and Mn femtosecond X-ray absorption spectroscopy (XAS) were performed on R2lox enzyme to follow the electronic and structural transformations associated with photochemical decarboxylation.
|Markus Meuwly, UniBA
|Quantitative Studies of Fast Reactions Relevant to Atmospheric Processes and Combustion from Molecular Simulations and Machine Learning
Reaction rates, distributions and cross-sections for atmospheric, hypersonic and combustion reactions are calculated from classical and quantum simulations as experimental approaches are limited at high temperatures (T ~ 20000 K). For this, reproducing kernel and neural network –(NN) based representations of high-level electronic structure calculations are used to investigate the dynamics for various channels of HONO and CHN2 decomposition. The ground and excited state potential energy surfaces are calculated at the multireference configuration interaction level of theory. These surfaces will be used for the dynamical simulations which are in turn used as the inputs for more coarse-grained investigations.
|Hans Jakob Wörner, ETHZ
|Attosecond coincident chiroptical spectroscopy
In this project we propose to undertake the production, characterization and application of isolated circularly polarized attosecond light pulses from a table-top high-harmonic generation (HHG) setup, combined with a photoelectron-photoion coincident momentum mircoscope.
|Rachel Grange, ETHZ
|Frequency Comb Generation in Polymeric Electro-Optic Devices
Optical frequency combs are sequences of evenly spaced frequency lines that have advanced applicability to spectroscopy and communications. They are efficiently generated in integrated electro-optic (EO) micro/nanodevices fabricated in crystalline platforms, which processing can be costly and time-consuming. In this context, polymeric materials are an interesting alternative due to advantages such as low cost, broad processability and the fact that molecules with high EO properties can be easily incorporated to polymeric matrices. This way, the goal of this project is to realize EO frequency combs in all-polymer devices fabricated by a bottom-up approach, aiming to reach performances comparable to the state-of-the-art in crystalline devices.
|Hans Jakob Wörner, ETHZ
|Theory of attosecond dynamics in liquids
Recent experimental advances in attosecond science have allowed the study of electronic dynamics in liquids on its intrinsic time scale. In parallel with the experimental progress, new theoretical models are required. We use, and extend, the existing theoretical methods in order to explain the experimental results measured in liquid water. This includes ab initio calculations of the photoionisation time delay from liquid and gas-phase water on different theoretical levels, such as using the Hartree–Fock method, direct solution of the time dependent Schrödinger equation, Monte Carlo simulations etc., where we focus on electron scattering and transport effects as well as on solvation effects.
|Christoph Bostedt, EPFL
|Electronic to nuclear relaxation processes in nanoparticles followed with ultrafast X-ray scattering
The project is aimed at investigating the pathway of strong electronic excitations in core-shell nanoparticles. Light-induced non-thermal phase transitions are studied on the nanometer length and femtosecond time scale by X-ray pump-probe wide-angle scattering at Alvra end station of the SwissFEL, PSI. An aerodynamic lens injector is used to deliver single nanoparticles into the X-ray focus. After adapting the injector for use at Alvra with core-shell nanoparticles we will observe and characterise the light-induced structural dynamics in these nanoparticles.
|Thomas Feurer, UniBE
|Enhanced nonlinear THz light-matter interactions
The aim of the proposed research is to enhance and control light-matter interaction in the terahertz (THz) regime, specifically ultrafast nonlinear properties of hybrid materials and structures. This research must be based on a thorough understanding of the mechanisms behind the nonlinear properties of the different novel materials in the THz frequency regime. Amongst other aspects, I am particularly interested in exploiting the different phases of organic molecules and perovskites. The outcome of research leads to new ultrafast devices and will contribute to the tremendous growth of THz nonlinear photonics and further our understanding thereof.
|Rachel Grange, ETHZ
|Enhanced nonlinear photorefractive switching in nanostructured films and nanomaterials
The photorefractive effect in non-centrosymmetric materials is a well-established method to dynamically control the wavefront of a light beam with another beam of light, however it remains slow and requires large optical power. Nanostructured thin films and nanoparticles offer a platform to reduce power demands of several nonlinear processes by harnessing subwavelength localized electromegnetic modes. This project merges for first time the photorefractive effect with resonant nanostructures in order to improve the speed and reduce the optical power demands.
|Majed Chergui, EPFL
|Time resolved photoelectron spectroscopy of aqueous DNA bases with extreme ultraviolet probe
Attosecond transient absorption spectroscopy (ATAS) is used to observe photoexcited dynamics with outstanding time resolution. The main experimental challenge of this technique is that high-harmonic generation sources show significant instabilities, resulting in sub-par sensitivity when compared to other techniques. This paper proposes edge-pixel referencing as a means to suppress this noise. Two approaches are introduced: the first is deterministic and uses a correlation analysis, while the second relies on singular value decomposition. Each method is demonstrated and quantified on a noisy measurement taken on WS2 and results in a fivefold increase in sensitivity. The combination of the two methods ensures the fidelity of the procedure and can be implemented on live data collection but also on existing datasets. The results show that edge-referencing methods bring the sensitivity of ATAS near the detector noise floor. An implementation of the post-processing code is provided to the reader.
|Hans Jakob Wörner, ETHZ
|Searching for intermolecular coherence with attosecond soft X-ray spectroscopy
Iron sulfur proteins are ubiquitous in nature, performing essential roles in electron transfer processes, redox chemistry, regulatory sensing and catalysis. The metal active sites of these proteins range from simple single iron sites to complex eight iron clusters. Perhaps the most complex iron sulfur cluster that has been identified to date is the iron molybdenum cofactor (or FeMoco) of nitrogenase, which is capable of cleaving the strong triple bond of dinitrogen. The fundamental question that arises is how does nature evolve complexity in order to enable challenging transformations? In our view, a deeper understanding of the complex geometric and electronic structure of iron sulfur clusters requires the pursuit of novel experimental approaches for integrating their electronic structure in a detailed and quantitative fashion. To this end, we are applying both 2p3d and 1s3p resonant inelastic X-ray scattering (2p3d RIXS), in order to obtain deeper insights into the electronic structure of these important clusters. These data provide an experimental measure of the d-d transitions and allow for more detailed insights into the nature of the multiplet structure. The utility of these methods for understanding the electronic structure of nitrogenase will be highlighted. The challenges that RIXS spectroscopy presents for theoretical modeling will also be discussed.
|Ursula Keller, ETHZ
|Attosecond-Time-Resolved Solid State Photoemission
Attosecond transient absorption spectroscopy (ATAS) in a functionalized transition metal carbide Ti3C2Tx (MXene) reveals ultrafast element, site, and carrier-specific electron-phonon relaxations on the few-femtosecond (fs) timescale. Quantitative agreement with theory validates the experimental results and provides new insights towards engineering of electronic heat dissipation at atomic scale.
|Natalie Banerji, UniBE
|In-Situ Time Resolved Sum-Frequency Generation Spectroscopy of Organic Electrochemical Transitstors/Electrolyte Interfaces
We demonstrate that time-domain ptychography, when applied to a set of broadband vibrational sum frequency spectra, reconstructs amplitude and phase of the vibrational free induction decay from an interfacial sample with a resolution that is independent of up-converting pulse bandwidth and spectrometer resolution. These important improvements require no modifications to most standard homodyne setups, and the method is applicable to other coherent homodyne spectroscopies such as coherent anti-Stokes Raman spectroscopy and transient grating spectroscopy.
|Majed Chergui, EPFL
|Femtosecond fluorescence and photoelectron spectroscopy investigation of the photodynamics of methylated DNA
Femtosecond fluorescence upconversion spectroscopy in the UV spectral range provides a powerful tool into the complex nature of ultrafast molecular processes in biomolecules. Hereby, epigenetic modifications of DNA are of particular interest because of their key role in gene regulation. Methylation of DNA nucleobases acts as an energy sink, this extends the excited-state lifetime and enables enhanced risk of UV-induced photodamage. Combination with time resolved photoelectron spectroscopy in aqueous solutions enables to construct a complete image of the excited state dynamics of methylated and partially methylated DNA oligonucleotides and strands.
|Paul Beaud, PSI
|Investigation of terahertz acoustic strain waves by ultrafast optical pump-probe spectroscopy and femtosecond x-ray scattering techniques
Modern techniques for the investigation of correlated materials in the time domain combine selective excitation in the THz frequency range with selective probing of coupled structural, electronic and magnetic degrees of freedom using x-ray scattering techniques. Cryogenic sample temperatures are commonly required to prevent thermal occupation of the low energy modes and to access relevant material ground states.
|Natalie Banerji, UniBE
|Ultrafast Terahertz (THz) spectroscopy and structural dynamics of 2D conducting polymers
The main goal of this project is to investigate the mechanism of charge carrier transport in two-dimensional (2D) conducting polymer films. Using time-domain terahertz (THz) spectroscopy and optical-pump-terahertz-probe (OPTP) spectroscopy we aim to study short-range charge carrier mobility in these materials. Secondly, to study the effect of polymorphism on charge transport, we plan to investigate the functional dependence of charge carrier mobility on phase transitions using temperature dependent THz spectroscopy. In the last phase of project, we will probe the structural dynamics in polymer films using ultrafast x-ray diffraction measurements.
|Markus Meuwly, UniBA
|Quantitative Atomistic Simulations for Condensed-Phase Systems using Machine-Learning Energy Functions
My work is concerned with the accurate description of intermolecular electrostatic multipole interactions and potential energy functions for molecular dynamics simulations of condensed phase systems. I combine the latest developments of the (minimal) distributed charge model ((M)DCM) with the reproducing kernel Hilbert space (RKHS) model and aim to extend its applicability to fundamental chemical reactions and to tune the energy functions quality through morphing schemes. My implementation will be validated by comparing experimental with computed 2D-IR spectra of aqueous N-methyl-acetamide solutions and KSCN in water/acetamide eutectic mixtures and applied on recombination reactions of CO+O on water ice surfaces.
|Ruth Signorell, ETHZ
|Electron scattering in molecular clusters and particles
The project aims to study electron dynamics in molecular clusters of growing size with angle resolved velocity map imaging of photoelectrons. This technique provides information on solvation effects in photoelectron spectra of molecular clusters.
|Urs Staub, PSI
|Ultrafast spin dynamics in a room-temperature multiferroic revealed by resonant x-ray diffraction
The manipulation of magnetization is the most important principle for current data storage technologies. Therefore, the possibility of an ultrafast control of magnetism by using optical methods has created a recent major interest in the field of condensed matter physics. One novel way for ultrafast control is to utilize an electromagnon excitation, an electric-dipole active spin excitation that exists in magnetoelectric multiferroics. This project aims at clarifying spin dynamics at an electromagnon excitation in a multiferroic hexaferrite, which has exceptionally large resonator strength and therefore suggests large-amplitude spin precession, by time-resolved resonant x-ray diffraction.
|Fabrizio Carbone, EPFL
|Imaging Ionization Dynamics with Attosecond Electron Pulses
Strong field physics in nanophotonic systems is opening a new frontier in optical physics, offering the ability to tailor electric fields and currents on the attosecond timescale and nanometre length scale. However, current attosecond probes lack the necessary spatial resolution to image such processes. To solve this, I am developing a source of attosecond electron pulse trains within a transmission electron microscope that will be used to probe the attosecond-nanometre dynamics of strong field ionisation in nanosystems. Studying these dynamics will not only shed light on fundamental light matter interactions in this regime, but also have an impact on future nanophotonic technology and ultrafast electronic devices.
|Ruth Signorell, ETHZ
|Electron Dynamics in Water Droplets
This project aims to develop photoelectron imaging of size-selected liquid droplets as a method to study the ultrafast dynamics of electrons in solution by exploiting the characteristic optical properties of droplets, and to try and answer fundamental questions about low energy electron scattering in liquids, solutions and across interfaces. This is a novel and promising technique with the potential to access uniquely comprehensive information about the solvent environment that has been unobtainable previously.