Seminars

TH-Seminar: Professor Philippe Schwaller

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TH-Seminar: Professor Harald Oberhofer

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From Levinthal’s Paradox to the Enigma of Disappearing Polymorphs: Using Minima Hopping to Explore the Synthesizability and Stability of Materials

Each local Minimum on the potential energy surfaces corresponds to a stable structure. In a theoretical structure search one typically finds a number of low energy minima that is much larger than the number of experimentally known structures. [more]

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Ultrafast Exciton Dynamics in Moiré Heterostructures: a Time-resolved Momentum Microscopy Study

Transition metal dichalcogenides (TMDs) are an exciting model system to study ultrafast energy dissipation pathways, and to create and tailor emergent quantum phases [1,2]. The versatility of TMDs results from the confinement of optical excitations in two-dimensions and the concomitant strong Coulomb interaction that leads to excitonic quasiparticles with binding energies in the range of several 100 meV. [more]

Hydrogen-Involved Surface Processes on Model Catalysts

The first topic of this talk is focused on the atomic-scale processes of dissociative adsorption and spillover of hydrogen on the single atom alloy catalyst (SAAC) Pd/Cu(111) [1]. The hydrogen spillover on the Cu(111) surface from the Pd site was successfully observed in real-time using infrared reflection absorption spectroscopy (IRAS) at 80 K. The observed chemical shifts of Pd 3d5/2 in X-ray photoelectron spectra (XPS) indicate that H2 is dissociated and adsorbed at the Pd site initially. [more]

Department Seminar - Twisted Tessellations - Coherent Control of the Translational and Point Group Symmetries of Crystals with Light

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Semiconductors and Topological Insulators for Infrared and Terahertz Metamaterials

When working in the infrared (IR) or terahertz (THz) spectral ranges, traditional optical materials like gold and silver have extremely large and negative permittivities. This means it is difficult to use these materials for plasmonics or hyperbolic metamaterials, both of which require materials with relatively small and negative permittivities. We must therefore explore alternative materials. In this talk, I will focus on two classes of materials: heavily-doped III-V semiconductors for the IR and topological insulators for the THz. [more]

Rovibronic Transitions in Molecules: Toward an Exact Approach

Molecules exhibit complex structural and dynamical behavior manifested in their degrees of freedom. The common approach to help us understand this complexity is to start with a zero-order approximation. Beyond the zero-order picture, the voyage to explore the molecular world is just about to begin. [more]

Tuning the Polarity of Porous Materials to Impact Adsorption, Diffusion, and Catalysis

Ordered mesoporous (organo)silicas provide a highly tunable platform to modulate the hydrophobicity of their surfaces, through thermal control of surface hydroxyl density as well as the incorporation of organic framework linkers. [more]

Electrochemical surface science of platinum electrodes

This talk will discuss recent insights into the electrochemistry of platinum, highlighting three topics. [more]

Vibrational Circular Dichroism of Molecular Crystals: The Interplay of Symmetry and Chirality

Chiroptical spectroscopy provides an increasingly important, cost-effective alternative for the study of chiral substances in the solid state. In recent years, vibrational circular dichroism (VCD) – the chiral form of IR absorption spectroscopy – has come into focus as a very sensitive probe of molecular conformation and environment. [more]

Machine Learning Models of Many-body Atomic and Electronic Interactions

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Single photon hot electron ionization of fullerenes

The separation of the time scales of electronic and nuclear motion in clusters and molecules opens the possibility that the electrons can form a transient and highly excited subsystem coexisting with cold nuclear degrees of freedom. [more]

An Atom's Eye View of Electrochemical Energy Transformations

The transition away from fossil fuels will provide the defining challenge for the next generation of chemists and engineers, and electrochemical technologies are crucial for this transformation. By providing a link between (renewable) electricity sources and chemicals, these technologies allow not only for storage and transportation of energy, but also provide routes to synthesize a wide range of chemicals and materials that today are integrally reliant upon fossil fuels. [more]

Ultrafast Structural Dynamics of Molecular and Biomolecular Systems

Observing molecular dynamics experimentally with both, highest spatial and temporal resolution is one of the biggest challenges in chemistry and biochemistry. Understanding and resolving structure-dynamics relationships will help to further understand molecular function. Few experimental methods allow to resolve multi-scale dynamics and structural information in the same experiment. [more]

A new experiment to measure parity violation in trapped chiral molecular ions

The weak force is predicted to give rise to slightly different structures for left and right-handed chiral molecules, contrary to the common conception that enantiomers are perfect mirror images. [more]

An Experiment to Measure the Electron's Electric Dipole Moment Using an Ultracold Beam of YbF Molecules

The fact that more matter than antimatter has been produced in the early stages of the universe is unexplained and known as the matter-antimatter-asymmetry problem [1]. One precondition is the combined violation of charge conjugation and parity (CP-violation) which is too small in the Standard Model. In almost all theories, CP-violation is also a precondition for the electron to have an electric dipole moment (de). [more]

Coupling the Time-Warp Algorithm with the Graph-Theoretical KMC Approach for Catalysis Simulations on Mega-Lattices and Beyond

Kinetic Monte-Carlo (KMC) simulations have been instrumental in multiscale catalysis studies, enabling the elucidation of the complex dynamics of heterogeneous catalysts and the prediction of macroscopic performance metrics, such as activity and selectivity. However, the accessible length- and timescales are still limited, and handling lattices containing millions of sites with “traditional” sequential KMC implementations becomes prohibitive due to large memory requirements and long simulation times. [more]

THz SASE and seeded FEL based on high brightness photo injector PITZ

The Photo Injector Test Facility at DESY in Zeuthen (PITZ) develops a prototype of an accelerator-based high-power tunable THz source for pump-probe experiments at the European XFEL. [more]

Tailoring Opto-electronic Properties of 2D Semiconductors in van der Waals Heterostructures

The opto-electronic properties of the transition metal dichalcogenides (TMDs) are sensitive to their environment. For example, the presence of graphene in the vicinity of the TMDs modifies their exciton binding energy and the magnitude of the bandgap via external dielectric screening. [more]

Perovskites as Supports for Single-atom Catalysis

Perovskite surfaces attract attention in the catalysis community due to these materials’ promising chemical properties, good ability to separate electron-hole pairs in light harvesting, and the presence of ferroelectricity in many perovskites. While perovskites possess a unique set of interesting bulk properties, their surfaces are much less understood; the main open questions are their structural stability and associated chemical reactivity and catalytic selectivity. [more]

Fully Quantum (Bio)Molecular Simulations: Dream or Reality?

The convergence between accurate quantum-mechanical (QM) models (and codes) with efficient machine learning (ML) methods seem to promise a paradigm shift in molecular simulations. Many challenging applications are now being tackled by increasingly powerful QM/ML methodologies. These include modeling covalent materials, molecules, molecular crystals, surfaces, and even whole proteins in explicit water (https://arxiv.org/abs/2205.08306). [more]

Laser spectroscopy of radioactive atoms and molecules at CRIS-ISOLDE

MP Seminar
Precision experiments based on heavy and polar diatomic molecules have been proposed as a promising pathway to pin down the level of fundamental-symmetry violations in the Universe. [more]

Constructing Defect Phase Diagrams from Ab Initio Calculations

Thermodynamic bulk phase diagrams have become the roadmap used by researchers to identify alloy compositions and process conditions that result in novel materials with tailored microstructures. [more]

Ultrafast molecular chirality: a topological connection

I will describe our very recent results on marrying chiral and topological properties in ultrafast electronic response of chiral molecules in gas phase and show that it brings such benefits as new highly efficient (not relying on interaction with magnetic field) and robust chiral observables, in contrast to standard chiroptical methods. [more]

New ’Low-Cost’ Electronic Structure Methods for Large Systems

All widely used semi-empirical quantum chemical methods like PM6, DFTB, or GFN-xTB are formulated in a (almost) minimal basis set of atomic orbitals, which limits the achievable accuracy for many important chemical properties. [more]

Pathways to Enhance Electrochemical CO2 Reduction Identified Through Multi-Scale Modeling Pathways to Enhance Electrochemical CO2 Reduction Identified Through Multi-Scale Modeling

Multi-physical transport processes on multiple scales are occurring in electrochemical devices and components for CO2 electroreduction. These coupled transport processes determine the local environment in the catalyst layer and subsequently also the reaction rates at the catalytic sites. [more]

Structure and Electronic Properties of Ultrathin Indium Films on Si(111)

Ultrathin metal films on atomically flat semiconductor substrates have been of great interest to investigate physical properties of two-dimensional (2D) metals. Indium-adsorbed Si(111) surfaces are one of the most explored metal/semiconductor systems. [more]

Four short presentations around the topic ISSP

Dr. Adris Anspoks: Short overview about ISSP // Dr. Aleksejs Kuzmins: X-ray absorption spectroscopy // Dr. Anatolijs Šarakovskis: overview about their activities in spectroscopy // Dr. Gints Kučinskis: Electrochemistry & batteries [more]

Solid-state NMR spectroscopy: Chemical shift and other parameters as structural and reactivity descriptors

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Acetylene semi-hydrogenation on intermetallic compounds

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

(Electro)catalytic model systems

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Fully-atomistic Light-driven Dynamics in Plasmonic Cavities and Interfaces

The study of confined fields in plasmonic nanocavities and their interaction with molecules and nanostructures is an area of research with vast applications, including enhanced spectroscopy techniques as well as photoinduced/photocatalytic non-equilibrium phenomena. From the theoretical perspective, either classical electromagnetic models or atomistic/quantum descriptions are usually considered. However, in many cases these models ignore the electronic and nuclear quantum effects arising from the chemical nature and dynamics of a junction, such as tunneling, adsorption geometry, structure of the interface, vibrations, etc., or include them only approximately. Hence, a full quantum dynamical description is sometimes inescapable. [more]

Synchrotron-based x-ray spectroscopy methods and experiments for in situ and operando investigations

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

In situ studies of Cu catalysed CO2 electroreduction bysoft X-ray STXM and spectro-ptychography

Soft X-ray scanning transmission microscopy (STXM) is a powerful tool for nanoscale materials analysis. [more]

X-ray scattering methods for operando studies of catalysts

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Bridging the materials and pressure gaps in oxide surface chemistry using IR spectroscopy: From model systems in ultra-high vacuum to in-operando studies at technologically relevant pressures

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Synthesis of nanostructured films by templating approaches

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Surprising Elements of Light

Light-driven chemical reactions power all life on earth and photochemistry has been intensely studied for more than a century, but light continues to provide surprising possibilities in driving and monitoring chemical reactions. [more]

In-situ transmission electron microscopy in heterogeneous catalysis

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Multi-Scale Modeling of Heterogeneous Catalysis

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Magnetism from First-principles

Development and engineering of new magnetic materials is one of the main goals in modern condensed matter physics. Thereby, first-principles simulations play a significant role in the design of new materials. Nowadays first-principles methods based on the density functional theory can provide very accurate information about electronic and magnetic properties of realistic systems and has become a major supplement and alternative to the experiment. [more]

Functional thin films and electrocatalysts by a soft molecular precursor approach

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Polarons Imaged in Real Space by Combined AFM/STM

Polarons [1] are quasiparticles that form in ionic lattices due to the interaction of excess charges with lattice distortions. This leads to a spatial confinement of the charge and appearance of many novel phenomena. In past decades, polarons turned out to play an important role in electrical transport, optical properties, organic electronics, catalysis, or in exotic materials properties such as colossal magnetoresistance or high-Tc superconductivity. [more]

Kinetic analysis and digital catalysis

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Learning Chemistry from a Computer: Recent Applications of Automatic Mechanism Generation for the Microkinetics of CO2 Methanation on Nickel

Microkinetic mechanisms in heterogeneous catalysis can be incredibly complex, and the development of these mechanisms raises many problems. How do you determine which species and reactions to include? How do you obtain the corresponding parameters? [more]

Fully Quantum (Bio)Molecular Simulations: Dream or Reality?

The convergence between accurate quantum-mechanical (QM) models (and codes) with efficient machine learning (ML) methods seem to promise a paradigm shift in molecular simulations. Many challenging applications are now being tackled by increasingly powerful QM/ML methodologies. These include modeling covalent materials, molecules, molecular crystals, surfaces, and even whole proteins in explicit water (https://arxiv.org/abs/2205.08306). [more]

Multiphase chemistry in cold parts of the atmosphere:Supporting field and modeling scientists with results from X-ray excited photoelectron spectroscopy

AC Seminar
Snow may hold impurity deposits, such as sea salt aerosol, which show vivid chemistry. Snow's porosity guarantees the efficient gas exchange of reaction products with the overlaying air. That snow thus acts as a chemical reactor on Earth with impacts on air quality, climate, and geochemical cycles has long been recognized. X-ray excited electron spectroscopy at near ambient pressure offers the possibility to investigate the underlying processes at surfaces of atmospheric relevance with high sensitivity and chemical specificity. This approach thus fills a unique gap in atmospheric science.Here, I will present the results of our work at the Swiss Light Source tackling 2 seemingly simple questions: 1) At which temperature do aqueous solutions freeze, and 2) How do acidic trace gases dissociate at ice surfaces? [more]

Collective States in Self-assembled Nanomaterials for New Functionalities in Vibrational Spectroscopy and Light-matter Coupling

Collective states are key to understand properties of materials across different length scales. In my talk, I will give an overview of different functionalities that emerge from collective states, with prospects for vibrational spectroscopy and engineering material properties with light. [more]

Oxide epitaxy via pulsed laser deposition for atomically-defined oxygen evolution catalysts - an opportunity for model systems and beyond

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Bridging scales from surface science to atmospheric chemistry and climate

Joint Seminar of AC and Theory
The development of ambient pressure X-ray photoelectron spectroscopy has from the beginning been motivated and justified by the context of atmospheric sciences, apart from other areas of fundamental and applied surface science. This has come in parallel with the recognition of important surface catalyzed processes in the stratosphere that are essential in ozone destruction. [more]

Picosecond Interfacial Dynamics in Crowded Lipid Membranes Probed with Ultrafast 2D Infrared Spectroscopy

Lipid membranes are much more than barriers between cell compartments, they are integral components of the cell involved in key functions such as signaling, transport, and sensing. Membranes are composed of hundreds of different lipid species and contain thousands of proteins. The biophysical implications of membrane heterogeneity are not fully understood. Our group uses 2D IR spectroscopy to probe the local hydrogen-bond dynamics at the lipid-water interface. [more]

Electron Paramagnetic Resonance for Catalysis Research

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Quantum control of ultracold ion-atom collisions

Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics and chemistry [1]. Reaching the ultracold s-wave quantum regime has been one of the most critical challenges in this field for a long time. Unfortunately, the lowest attainable temperatures in experiments using the Paul ion trap are limited by the possible rf-field-induced heating related to the micromotion. [more]

Probing Electronic Structure and Magnetism in Low Dimensionality - An Experimental Approach

The ever-growing need for next-generation electronic and magnetic devices calls for new solutions for the engineering of quantum materials, in terms of miniaturization, energy consumption and speed compared to reference benchmarks, e.g. 18 ps for the Larmor magnetization switching. A new paradigm has emerged: the effect of the decrease of dimensionality in magnetic materials is recently being given a large deal of attention. [more]

Towards STM of catalytic reactions

CatLab Highlight Lecture
Scanning tunneling microscopy (STM) regularly offers atomic resolution, can work at high pressures and only interacts weakly with matter - seemingly perfect conditions for gaining access to the microscopic processes on a catalyst surface. On the other hand, the number of examples in which working catalysts have actually been imaged with the STM has remained small. [more]

Chemical Physics far from equilibrium

CatLab Highlight Lecture
In this talk, I will discuss recent examples from electrochemistry in which the system’s behavior is ‘more than the sum of its parts’ and nonlinear interactions generate complex forms of organization. Thereby, I will highlight general conditions that generate certain types of cooperative phenomena. Experimental examples range from electrocatalytic reactions, to the electrooxidation of photoelectrodes. The patterns forming can be understood in the framework of ‘many particle models’ with nonlinear and nonlocal interaction between the particles, as they are often found in electrochemical systems. [more]

Facing the Climate Challenge - Tasks and Opportunities for Industrial Oxidation Catalysis

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

Investigating Ultrafast Electron and Phonon Dynamics at the Atomic Scale

Electrons, phonons, and their mutual interactions are crucial for the complex phenomena in strongly correlated materials. In this talk, I will show that electron and phonon dynamics can be investigated at the atomic scale by combining THz pump-probe spectroscopy and a scanning tunneling microscope (STM) [1,2]. [more]

Thin film technolgy meets catalysis: Focus on Thin film Growth and Properties

Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures around the classical fundamentals of heterogeneous catalysis, such as adsorption, kinetics, structural and surface analysis, and the challenges of thin film technology, such as material development and methods of modern thin film analysis. [more]

THz-VUV Ellipsometry and THz Electron Paramagnetic Resonance Ellipsometry Characterization of SiC and Other Wideband Gap and Ultrawideband Gap Materials

The control over electrical conductivity is critical key to enabling gallium oxide and related materials for high power electronic devices. Understanding the influence of dopants and defects onto the electrical and electronic properties is therefore of paramount importance [1]. Identifying defects and their local electronic properties remains a challenge. [more]

Ultrafast Electron Dynamics in Quasi-two-dimensional Quantum Materials

Quantum materials are solids with tantalizing properties arising from special symmetry, dimensionality, topology, and many-body interactions between elementary degrees of freedom (charge, spin, orbital, and lattice). Gaining a microscopic understanding of quantum materials is critical as it implies the possibility of designing materials with desirable properties. [more]

DFTB+, the Fast Way of Quantum Mechanical Simulations

The Density Functional Tight Binding (DFTB) method [1] is an approximate Density Functional Theory (DFT) based framework, which allows for quantum mechanicalsimulations of large systems being typically two or three orders of magnitudefaster than comparable ab initio DFT calculations. [more]

Operando SXRD/XAS studies of CoOx epitaxial thin films for OER electrocatalysis

Cobalt oxides are among the best earth abundant catalysts for the oxygen evolution reaction (OER) in alkaline and neutral electrolytes. We have undertaken operando studies of two dimensional epitaxial cobalt oxide films [1-2] to gain insights into some questions that remain in debate. [more]

The Value of Information: From Statistics to Algorithms

A fundamental question in data science is: how much information can one extract from the data that one collects? [more]

Quantum-Chemical Methods for Large Systems: Low-, Linear-, and Sublinear-Scaling Methods

An overview of our recently developed low-, linear-, and sublinear-scaling methods ranging from HF, DFT, MP2 to RPA is given. These methods allow — also in combination with graphics processing units (GPUs) — for the efficient description of large systems at QM and QM/MM levels, where QM spheres with typically 500-1000 atoms are necessary for reliable studies. [more]

New Concepts in Battery and Solid Electrolyte Design

Solid electrolytes (SEs) are a key component of all-solid-state batteries (ASSBs), which promisehigher energy density along with safer operation compared to commercial Li ion batteries. As theASSB technology matures, research in the field gravitates towards questions regarding stability,scalability, and integration of solid electrolytes into ASSBs with extended cycle life. [more]

Design of Novel Hybrid and Solid State Battery Materials

Next generation of energy storage devices may largely benefit from fast and solid Li+ ceramic electrolyte conductors to allow for safe and efficient batteries and fast data calculation. For those applications, the ability of Li-oxides to be processed as thin film structures and with high control over Lithiation and phases at low temperature is of essence to control conductivity. [more]

Lightwave-Driven Scanning Tunneling Spectroscopy for Ultrafast Surface Science on the Atomic Scale

The development of novel nanoscale systems with technologically relevant properties has created a demand for powerful experimental technique’s capable of extreme spatio-temporal resolution. Scanning tunneling microscopy (STM) has become an era-defining surface characterization tool capable of extracting the local density of states (LDOS) with ångström-scale spatial resolution. [more]

Understanding of Energy Transfer Dynamics in Luminescent Eu(III) Complex Doped Host-Guest Film

Trivalent europium (Eu(III)) complexes are expected to be used as light-emitting materials such as organic light emitting diodes (OLEDs) because of their high color purity. The complexes are sensitized by the antenna effect, utilizing energy transfer from antenna ligands to a metal center. In the emitting layer of OLEDs, guest emitters are doped in host molecules, and intermolecular energy transfer also occurs. [more]

Solving Electrochemistry Puzzles by First-Principles Multi-Scale Modeling

Electrochemistry has become the most-promising prospect towards a sustainable energy landscape. Still, most processes have not been optimized to a level that could compete with fossil fuels. Consequently, substantial optimization of electrode materials, electrolytes and electrochemical cells is required on all size scales to quickly reach the industrially desired performance. [more]

Emergent Electronic and Spin States Revealed by Spin Resolved Scanning Tunneling Spectroscopy

  • FHI/IMS Joint Online Seminar
  • Date: Jul 21, 2022
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Prof. Sujit Manna
  • Department of Physics, Indian Institute of Technology Delhi
Under special conditions, a fermion in a superconductor can separate in space into two parts known as Majorana zero modes (MZM), which are immune to decoherence from local noise sources and are attractive building blocks for quantum computers. Promising experimental progress has been made to synthesize topological superconductors that demonstrate Majorana zero modes in materials with strong spin–orbit coupling proximity coupled to superconductors. [more]

Understanding the Birth of the Catalyst during Pyrolysis Using Synchrotron X-rays

Transition metal-nitrogen-carbon materials (M-N-C catalysts) are promising electrocatalysts in electrochemical applications. High temperature treatment in inert environment (pyrolysis) is the most common method for the synthesis of M-N-C catalysts and critical to achieve high electrocatalyst activity and electronic conductivity. [more]

New Generation of Atomically Dispersed Electrocatalysts

Platinum Group Metal-free (PGM-free) catalysts have been extensively developed for both Proton Exchange Membrane (PEM) and Alkaline Exchange Membrane (AEM) fuel cells aiming automotive, stationary and portable applications. In this lecture we will address the critical challenges that our team has faced on the way to practical application of such catalysts. [more]

Understanding Correlation Among Electron-Phonon-Spin Degree of Freedom in Advanced Molecular Optoelectronics

  • IMS-FHI Joint Online Seminar
  • Date: Jul 4, 2022
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Kiyoshi Miyata
  • Department of Chemistry, Kyushu University
  • Host: Takashi Kumagai
Microscopic understanding of exciton and carrier physics in molecular materials for optoelectronics is a great challenge because of their complexity resulting from strong electron-phonon coupling and perhaps interaction to spin degree of freedom; [more]

The End of Ab Initio MD

A new computational task has been defined and solved over the past 15 years for extended material systems: the analytic fitting of the Born-Oppenheimer potential energy surface as a function of nuclear coordinates under the assumption of medium-range interactions, 5 ~ 10 Å. [more]

Single-Molecule Studies of Dissociation Reactions of O2 Molecules on Ag(110) by Electrons, Holes, and Localized Surface Plasmons

  • PC Department Online Seminar
  • Date: Jun 27, 2022
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Emiko Kazuma
  • Department of Applied Chemistry, The University of Tokyo
  • Host: Akitoshi Shiotari
A mechanistic understanding of the dissociation of O2 molecules adsorbed on metal surfaces is crucial not only for the precise control of oxidation reactions but also for the development of various heterogeneous oxidation catalysts. [more]

FHI Library Workshop: Open Access & Information Resources

This interactive workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Machine Learning (ML) for Simulating Complex Energy Materials with Non-Crystalline Structures

Many materials with applications in energy materials, e.g., catalysis or batteries are non-crystalline with amorphous structures, chemical disorder, and complex compositions, which makes the direct modelling with first principles methods challenging. To address this challenge, we developed accelerated sampling strategies based on ML potentials, genetic algorithms, and molecular-dynamics simulations. [more]

Fluxional catalytic interfaces and how they evolve under realistic conditions: insights from computational studies

Fluxionality, or the presence of and interconversion between multiple possible energetic configurations, is vital for understanding a catalyst as it operates under actual reaction conditions. [more]

Chemical challenges facing scalable hydrogen production with alkaline membrane electrolyzers

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under the locally acidic conditions of the ionomer. [more]

Hot Electrons in Surface Chemistry: From Molecular Scattering to Plasmonic Chemistry

Nonadiabatic effects that arise from the concerted motion of electrons and atoms at comparable energy and time scales are omnipresent in thermal and light-driven chemistry at metal surfaces. [more]

Water Flows in Carbon Nanochannels, from Carbon Memories to Quantum Friction

The emerging field of nanofluidics explores the molecular mechanics of fluids. This world of infinitesimal fluidics is the frontier where the continuum of fluid dynamics meets the atomic nature of matter, or even its quantum nature. Nature fully exploits the fluidic oddities at the nanoscale and it is capable of breath-taking technological feats using a fluidic circuitry made of multiple biological channels, such as ionic pumps, proton engines, ultra-selective pores, stimulable channels, ... [more]

Dynamic catalytic interfaces: ensembles of metastable states break the rules of catalysis

I will show that dynamic catalytic interfaces exhibit great structural fluxionality in conditions of catalysis, and populate many distinct structural and stoichiometric states, which form a statistical ensemble. [more]

FHI Library Workshop: Databases

Our workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Sub-molecular Imaging of Light-matter Interaction

  • FHI/IMS Joint Online Seminar
  • Date: May 9, 2022
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Anna Rosławska
  • Université de Strasbourg, CNRS, IPCMS
  • Host: Melanie Müller
Light-matter interaction plays a crucial role in the quantum properties of light emission from single molecules, and in electron-to-photon and photon-to-electron energy conversions. Such mechanisms are usually probed using optical methods, which are, however, spatially limited by diffraction to a few hundred nanometers. [more]

Machine Learning at the Atomic Scale: From Structural Representations to Chemical Insights

When modeling materials and molecules at the atomic scale, achieving a realistic level of complexity and making quantitative predictions are usually conflicting goals. Data-driven techniques have made great strides towards enabling simulations of materials in realistic conditions with uncompromising accuracy. [more]

On-Surface Chemistry of Helicenes

  • Department Online Seminar
  • Date: May 2, 2022
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Karl Heinz Ernst
  • EMPA, Dübendorft, Switzerland
  • Host: Martin Wolf
Surfaces functionalized with helicenes are of interest for chiroptical electronic devices or for electron-spin filtering. While self-assembled layers facilitate studying interesting phenomena, covalently linked chiral modified materials would be much more robust and therefore better suited for applications. [more]

Photochemistry and spectroscopy of molecules at surfaces – Insights (mostly) from ab initio molecular dynamics –

The interaction of adsorbates on solid surfaces with light is central to surface spectroscopy, surface photochemistry, and non-adiabatic surface science in general. In the present contribution, light-driven molecular adsorbates will be modelled (mostly) by ab initio molecular dynamics. A few examples will be highlighted: [more]

Ultrafast Lattice Dynamics and Microscopic Energy Flow in Ferromagnetic Metals and in an Anisotropic Layered Semiconductor

  • PC Department Online Seminar
  • Date: Apr 22, 2022
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Daniela Zahn
  • FHI Department PC
  • Host: Ralph Ernstorfer
In this talk, I will give an overview of my PhD thesis, focusing on two topics: lattice dynamics in black phosphorus and ultrafast energy flow in 3d ferromagnets. The layered semiconductor black phosphorus exhibits a peculiar structure with in-plane anisotropy. Here, we use femtosecond electron diffraction to access the lattice response to laser excitation. The optical excitation and subsequent electron-phonon coupling lead to a pronounced non-thermal state of the lattice, which is characterized by a transiently reduced anisotropy of the atomic vibrations. On timescales of tens of picoseconds, thermal equilibrium is restored via phonon-phonon coupling [1,2]. Our results yield insights into both electron-phonon and phonon-phonon coupling and provide pathways to control the timescale of lattice thermalization in black phosphorus. [more]

Femtosecond Infrared Spectroscopy of Photoinduced Intermolecular H+ Transport

Ultrafast intermolecular proton (H+) transport pathways of the bifunctional photoacid 7-hydroxyquinoline (7HQ) in polar protic methanol solvent are examined with femtosecond UV-pump/IR-probe spectroscopy. Following electronic excitation, 7HQ can be converted simultaneously into a strong acid and a strong base. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Time- and Angle-Resolved Photoemission Study on Bulk VSe2

  • PC Department Online Seminar
  • Date: Apr 4, 2022
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Wibke Bronsch
  • Elettra - Sincrotrone Trieste, Trieste, Italy
  • Host: Chris Nicholson
By means of time- and angle-resolved photoemission spectroscopy (tr-ARPES), we investigate the effect of the charge density wave (CDW) phase transition on the equilibrium and out-of-equilibrium electronic properties of the transition metal dichalcogenide VSe2. [more]

Machine-Learning Potentials: The Accurate, the Fast, and the Applied

Data-driven algorithms ("machine learning") are increasingly used in science and engineering for analysis, prediction, and control, enabling new insights and applications. A promising example are first-principles simulations of the dynamics of atomistic systems. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Library Workshop on Reference Management Systems

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

In Silico Design of Single-Atom- and Highly-Dilute-Alloy Catalysts: Success Stories and Opportunities for Innovation

Catalysis is undoubtedly at the heart of the chemical industry: out of all chemicals manufacturing processes, 85-90% are catalytic and about 80-85% thereof employ heterogeneous catalysts. Yet, developing catalysts for given applications is non-trivial, necessitating empirical and resource-intensive trial-and-error experimentation. Theory and simulation, on the other hand, can provide fundamental insight into the mechanisms underpinning catalytic function, and guide the design of catalytic materials for applications of practical interest. [more]

Near-field Optical Microscopy and its Recent Advances: High Speed Imaging and Broadband Measurements

Near-field optical microscopy (aperture-less type) enables optical analysis and imaging with the nanoscale spatial resolution owing to light field localized at a nanometric volume at a plasmonic tip apex. It has been recognized as a powerful analytical technique for a few decades since its invention, and has still shown tremendous progress, contributing to a wide variety of scientific fields. Its spatial resolution, for example, has been drastically improved in recent years, which now goes down to the single molecular level. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Analysis of thin films by in-situ IR spectroscopy

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Deposition and operando analysis techniques for solar fuels

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

X-ray microscopy

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Strong Coupling and Extreme Anisotropy in Infrared Polaritonic Media

  • PC Department Online Seminar
  • Date: Jan 24, 2022
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Joshua D. Caldwell
  • Vanderbilt University, Nashville, Mechanical Engineering Dept.
The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. In the infrared, this requires compression of the wavelength to length scales well below that of the free-space values. While traditional dielectric materials do not exhibit indices of refraction high enough in non-dispersive media to realize such compression, the implementation of polaritons, quasi-particles comprised of oscillating charges and photons, enable such opportunities. [more]

Diffraction methods and residual stress analysis of thin layers

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Data-Enabled Materials Structure-Property-Synthesizability Predictions

The constant demand for new functional energy materials calls for efficient strategies to accelerate the materials discovery. In addressing this challenge, materials informatics deals with the use of data, computations, and machine learning (complementary to experts’ intuitions) to establish the materials structure-property relationships and to make a new functional discovery in a rate that is significantly accelerated. [more]

Properties of thin films and their interfaces as revealed by X-ray spectroscopies

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Surface states conduction measurements by two-probe scanning tunneling microscopy with Ohmic contact

  • PC Department Online Seminar
  • Date: Jan 10, 2022
  • Time: 04:00 PM (Local Time Germany)
  • Speaker: Dr. Jo Onoda
  • University of Alberta, Canada
Relentless downscaling of conventional electronic devices demands continuous improvement in characterization of microscopic surface electronic properties. Moreover, in the pursuit of more exploratory device concepts such as atomic-scale logic gates [1] and memories [2] composed of dangling bonds on hydrogen-terminated Si surfaces there is great need for characterization of extremely small one- and two-dimensional structures. [more]

Electron microscopy in heterogeneous catalysis

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Excitons and Lattice Dynamics in Novel Semiconductor Materials Probed by Optical Spectroscopy

  • Department Online Seminar
  • Date: Dec 13, 2021
  • Time: 03:00 PM (Local Time Germany)
  • Speaker: Dr. Joanne Urban
  • École Normale Supérieure Paris-Saclay
2D layered semiconductors are both a fascinating platform to investigate quantum and dielectric confinement phenomena and versatile candidates for optoelectronic applications. Hybrid 2D layered perovskites combine large exciton binding energies with unique properties related to the dynamics of their soft, polar lattice. [more]

Nanovideography of ultrafast charge carrier dynamics in van der Waals materials

  • PC Department Online Seminar
  • Date: Dec 6, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Markus Huber
  • Universität Regensburg
The terahertz and mid-infrared spectral domain host a multitude of interesting low-energy elementary excitations, such as phonons, plasmons and magnons. Ultrafast optical spectroscopy has provided key insights into the dynamics of these collective excitations. Unfortunately, the spatial resolution of such (far-field) studies is intrinsically limited to the scale of the probing wavelength by diffraction. Thus, the optical response cannot resolve individual nano-objects, confined polariton waves, or local surface effects. [more]

Photoelectron spectroscopy in catalysis research

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Visualizing Electron Localization and Minibands in WS2/WSe2 Moiré Superlattices

  • PC Department Online Seminar
  • Date: Nov 29, 2021
  • Time: 09:00 AM (Local Time Germany)
  • Speaker: Conrad Stansbury
  • University of California, Berkeley
  • Host: Tommaso Pincelli
The ability to engineer flattened electronic bands by controlling interlayer effects in moiré superlattices of two-dimensional materials has opened the door for material physicists to understand and control correlated electron phenomena in an unprecedentedly broad class of materials. Despite wide-ranging transport and optical signatures of correlated phases, a holistic understanding of how exotic quantum phases emerge remains elusive. [more]

Vibrational spectroscopies in heterogeneous catalysis

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Launch of a new local data archive for catalysis research - A brief introduction

Recently, the more than 20-year-old data archive of the AC department was replaced by a new version. In the seminar, this new release will be briefly presented and users will have the opportunity to ask questions and make suggestions. This local data infrastructure will also be used by cooperation partners in the ISC department, at the BasCat laboratory of the TU Berlin and at HZB. Colleagues who do not use this archive are welcome to take a look at this type of data archiving, which is especially tailored to research data generated in the study of functional materials. [more]

Multilayer supramolecular architectures at device interfaces: Prospects for electron and phonon transport

  • PC Department Online Seminar
  • Date: Nov 22, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Prof. Carlos-Andres Palma
  • Institute of Physics Chinese Academy of Sciences & Humboldt-Universität zu Berlin
  • Host: Akitoshi Shiotari
Manufacturing atomically-precise functional nanoarchitectures with tailored physics at well-defined device interfaces is a frontier in bottom-up nanomaterial [1,2] and condensed matter design [3]. A long-standing challenge in the field is the integration of functional elements in proof-of-concept devices. One strategy to alleviate the cumbersome device integration of single-layered molecular systems, is to achieve increasing control over vertical supramolecular heterojunctions and multilayers, so as to transition from ‘on-surface’, to ‘out-of-surface’ surface science protocols. [more]

Thermal analysis

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Atomically-resolved interlayer charge ordering and its interplay with superconductivity in YBa2Cu3O6.81

  • Joint Seminar
  • Date: Nov 8, 2021
  • Time: 09:00 AM (Local Time Germany)
  • Speaker: Prof. Ya-Ping Chiu
  • Department of Physics, National Taiwan University, Taipei, Taiwan
  • Host: Takashi Kumagai
Joint seminar of Fritz Haber Institute and Institute for Molecular Science, Japan. Charge order (CO) has been recognized as one of the most important competing order in superconductive cuprates. In YBa2Cu3O6+x (YBCO), CO could only be investigated by x-ray diffraction in under-doped YBCO with low critical temperatures (TC), but not in highly-doped YBCO with high TC suitable for device applications, due to the competing superconductive phase. Therefore, the most fundamental physical mechanisms governing CO, for example, the role of so-called charge reservoir (Cu-O chain) layers in CO and the spatial interplay of CO and SC, in highly-doped YBCO are still unclear. [more]

Analysis of the bulk and defect structure of catalysts

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Data acquisition system in the AC department

In this seminar we want to present the possibilities of automatic data acquisition, data processing and storage in an archive.We will discuss current experiments with proprietary devices as well as systems with generic devices (MFCs, Temp-Controller).We follow the idea of the FAIR principle and want to create the conditions for the application of Big Data analysis and data mining methods.For this, reliable, reproducible data sets with high diversity are needed. To generate such data, handbooks are used in which the characterization of catalysts and the determination of kinetic data are precisely prescribed. These handbooks should specify the minimum data set that should be generated for each catalyst and how the measurements should be performed.To achieve these goals, various software and hardware components are needed. Here are some examples that will be presented in this talk: [more]

Synthesis of heterogeneous catalysts

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

Concepts in heterogeneous catalysis

CatLab Lectures Modern Methods in Heterogeneous Catalysis Research
Modern Methods in Heterogeneous Catalysis Research. A series of independent lectures on basic principles and new challenges in catalysis research. The lecture series is aimed at PhD students and scientists who are interested in interfacial phenomena and the design and investigation of functional 3D and 2D materials. [more]

The discovery and applications of topological quasiparticles by ultrafast microscopy

  • PC Department Online Seminar
  • Date: Oct 19, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Prof. Hrvoje Petek
  • University of Pittsburgh
  • Host: Martin Wolf
Surface plasmon polaritons (SPP) are composite electromagnetic field-charge density wave collective modes that propagate at metal/dielectric interfaces at the local speed of light. The circulation of their fields from transverse to longitudinal causes a transverse spin angular momentum (SAM) locking known as quantum spin-Hall effect, which embodies the property of evanescent waves, such as SPPs, that changing the sign of the photon momentum direction changes the sign of its spin. In other words, the oppositely propagating SPP waves possess the opposite spin. SPP fields can also carry optical angular momentum (OAM), which can focus them into plasmonic vortices. [more]

FHI Library Workshop: Information Resources & Open Access

This workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. The workshop will be held in the FHI library (building A) and lasts about 45 minutes. The number of participants is limited to five. Please register and inform us about your focus of interest.

Ultrafast Structural Dynamics of Elementary Water-Mediated Proton Transfer Processes

Proton transport between acids and bases in aqueous solution involves the exchange of protons, rearrangements of hydrogen bonds, and the changes in electron charge distributions of all molecules involved. Progress in the development of ultrafast structurally resolving techniques have enabled to follow in real-time the elementary individual steps in proton transfer that occur on femto- to picosecond time scales. Ultrafast probing in the mid-infrared has provided a wealth of information on hydrogen bond dynamics and proton transfer time scales. Recent progress in soft X-ray spectroscopy of solution phase acids and bases using novel flatjet technology has now made possible to locally probe electronic structure. I will showcase this with examples on proton hydration, and photoacid molecular systems, and indicate how further advances in ultrafast soft X-ray spectroscopy of solution phase proton transfer may be made. [more]

Vibrational exciton and polaron nano-imaging: a molecular ruler to image structure, coupling, and disorder in functional molecular materials

Properties and functions of molecular materials often emerge from intermolecular interactions and associated nanoscale structure and morphology. However, defects and disorder give rise to confinement and many-body localization of the associated wavefunction, disturbing the performance of, e.g., molecular electronic or photonic materials. Conventional microscopy and even nanoscopy lack spatio-spectral sensitivity to the low-energy and molecular length scales of intermolecular interactions, carrier-phonon coupling, and polaron formation, thus leaving a missing link between material structure and observed heterogeneity in the electronic or photonic response.We address these outstanding problems in several novel combinations of spatio-spectral and spatio-temporal infrared nano-imaging. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Controlling the uncontrollable: Quantum control of open systems

Quantum control addresses the issue of driving a system to a desired objective. Manipulation of quantum systems is achieved by coherent control which relies on constructive and destructive interference of the quantum amplitudes, i.e., quantum coherence. The key ingredient, coherence, is extremely sensitive to any external perturbation. In reality all quantum systems are open, thus, are subject to environmental effects. The interaction with the environment degrades the required agent, coherence, leading to a detrimental effect on coherent control. Quantum control of an open system is therefore a challenge. For this study we employ a thermodynamically consistent master equation. In this framework, the open system dynamics depend on the control protocol due to the dressing of the system by the drive. This interrelation serves as the key element for control. The influence of the external drive is incorporated within the dynamical equation, enabling an indirect control of the dissipation. The control paradigm is displayed by analyzing entropy changing state to state transformations, heating and cooling N-levels systems, accelerating the approach to equilibrium. Following, we study the generation of quantum non-unitary maps via coherent control. These include both reset maps with complete memory loss. The other extreme where the control is optimized to minimize the dissipation is demonstrated by a single and two qubit unitary maps. [more]

Ultrafast Infrared Spectroscopy at the Nanoscale

  • Joint Online Seminar
  • Date: Sep 6, 2021
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Jun Nishida
  • Center for Mesoscopic Sciences, Institute for Molecular Science, Japan
  • Host: Fritz Haber Institute
Emerging functional materials exhibit “liquid-like” dynamics associated with their soft lattice structures, often with spatial heterogeneity at length scales ranging from tens to hundreds of nanometers. Yet, tools to characterize such dynamical disorder have not been established. While nonlinear infrared spectroscopy has elucidated dynamics of liquids and solutions over the past decades, the limited sensitivity and the fundamental diffraction limit have hampered its applications to material systems at the nanoscale. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

How to publish your science: A guide to writing your first re-search article, and every article after that

Scientific writing is an integral part of any researcher’s career, aimed at communicating original research for peer review. Well written articles backed by citable scientific data help expedite peer collaboration and advancements in any field. [more]

Engineering pi-conjugated nanomaterials on surfaces

Joint seminar of Fritz Haber Institute and Institute for Molecular Science, Japan. The design of pi-conjugated nanomaterials is at the vanguard of science and technology taking into account the interest in optoelectronics,nanomagnetism, quantum information and non-trivial quantum phases of matter.In this talk I will revise our efforts in the last couple of years to engineer on surfaces pi-conjugated polymers and networks that could expressnon-trivial topological quantum classes. [more]

Thermodynamic properties by on-the-fly machine-learned interatomic potentials: thermal transport and phase transitions

[more]

Computational Understanding of Electrochemical Energy Storage Materials

The complete electrification of the transport sector will require batteries that can be made from abundant chemical species and exhibit significantly greater energy density than current Li-ion batteries. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Towards ex-machina computations of transport and transformations in complex materials

[more]

Soft X-ray Photoelectron Momentum Microscopy: resonating valence band element selectively

  • Joint Seminar
  • Date: Jun 7, 2021
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Dr. Fumihiko Matsui
  • UVSOR synchrotron facility, Institute for Molecular Science, Japan
  • Host: Takashi Kumagai
Joint seminar of Fritz Haber Institute and Institute for Molecular Science, Japan. Photoelectron micro-spectroscopy and spectro-microscopy are important approaches for elucidating the local electronic properties of micro- and nano-structures. By combining the photoelectron momentum microscope (PMM) and a soft X-ray synchrotron radiation, three-dimensional momentum-resolved photoelectron spectroscopy with a microscopic field of view is realized. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

FHI Library Online Workshop: Reference Management Systems

This course explains what reference management systems (also known as bibliographic or citation management software) are, why they are useful for any kind of research, and what to look out for when considering the use of one of the numerous available bibliographic management applications. The two systems, EndNote and Mendeley, are demonstrated as examples. More details on how to join the workshop will be announced by e-mail or contact the library team.

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

An Alternative Route out of Equilibrium: Probing Uniaxial Strain Effects in TMDs with ARPES

The fascinating properties of emergent phases in condensed matter systems can give usconsiderable insight into the physical mechanisms underpinning them. A central scientific goalof recent decades has been to employ external perturbations such as doping, pressure,magnetic fields and intense laser pulses in order to push materials away from their equilibriumconfigurations, revealing further insights into the mechanisms relevant to stabilising thesephases. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Simulating angle-resolved photoemission in real-time from first principles

  • PC Department Online Seminar
  • Date: May 10, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Stephan Kümmel
  • University Bayreuth
Photoemission experiments are often interpreted by relating the measured quantities to orbitals and eigenvalues of the studied system. After a short review of this usual interpretation, the talk will take a look at how photoemission can alternatively be calculated as a process in real time. Using time-dependent density functional theory, the escape of electrons after an excitation can be simulated as a time-dependent process and the kinetic energy of the outgoing wave packets can be analyzed with angular resolution. This allows to simulate angle-resolved photoemission and study, e.g., final state effects and circular dichroism. [more]

Blending Old Concepts with Data-driven Approaches to Discover and Classify Homogeneous Catalysts

Sabatier’s principle,[1] developed in the first decades of the 20th century, states that an ideal catalyst should bind a substrate neither too strongly nor too weakly. Today, this simple idea provides the fundamental underpinning for “volcano plots”,[2,3] which are abundantly used in heterogeneous and electrocatalysis.[4] [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Scanning Probe Microscopy Investigation of Nonahelicene on Ag(110)

  • PC Online Talk
  • Date: Apr 29, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Maximilian Halbauer
  • FHI Department PC
Carbohelicenes are an important class of organic chiral molecules. They possess a conjugated aromatic backbone that is arranged in a helical shape. This results in strong chiroptical responses and makes them attractive targets for physical devices. Moreover, their shape resembles that of macroscopic springs, although their exact mechanical properties are unknown. [more]

Tailoring the Luminescence of Atomically Thin Semiconductors at the Sub-nanometer Scale

  • PC Department Online Seminar
  • Date: Apr 26, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Luis Parra Lopez
  • Institut de Physique et de Chimie des Matériaux de Strasbourg
Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are appealing systems for the investigation of strong light-matter interactions. Indeed, when thinned down to the monolayer limit, these materials undergo an indirect-to-direct bandgap transition and therefore, their light emission yield is enhanced [1]. [more]

Theoretical Perspectives on Proton-Coupled Electron Transfer

Proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of chemical and biological processes. This talk will focus on the theory of PCET as well as illustrative applications to catalysis and energy conversion processes. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Advancing fundamental science with Machine Learning at DeepMind

Deep learning has had a transformative impact in computer science and is recently being applied to the natural sciences. In this talk, I will give an overview of recently published work on applying Machine Learning techniques to fundamental science problems at DeepMind. I will cover: super-human Quantum Dot tuning, advances in quantum Monte Carlo with neural network ansatz, transfer learning for predicting experimental material properties, and finally, touch upon recent advances in protein structure prediction. These case studies will hopefully allow me to exemplify the three kinds of impact that we can expect in future years: automating the experimental research pipeline, exploiting the representation power of neural network as function forms and finally extracting knowledge from data. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Accurate Description of Correlated Physics of Bulk Materials using Diagrammatic Methods and Quantum Embedding

This talk will give an overview of continuing work in the Chan group to describe correlated electron materials with high-level quantum chemistry methods. [more]

Dynamic Screening of Quasiparticles in WS2 Monolayers

  • PC Online Talk
  • Date: Mar 18, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Stefano Calati
  • FHI Department PC
The low dimensional nature of TMDCs and the resulting reduced screening influence their non-equilibrium optical properties, as dynamic screening by photoexcited quasiparticles governs the transient response. Here, we investigate the respective roles of excitons and quasi-free carriers on the dynamic response of WS2 monolayers on SiO2. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Towards Predicting the Charge of Electrochemical Interfaces

The charge of an electrochemical interface helps to determine its chemical reactivity and macroscopic electrostatic properties. However, predicting the charge at an electrochemical interface is challenging because it generally requires both the electronic structure of the interface, and the thermodynamically averaged spatial distribution of the electrolyte. Due to this difficulty, interfacial charge prediction remains an open problem in computational electrochemistry. [more]

Excitonic Properties of Localized Emitters from Monolayer WSe2 an WSe2/MoSe2 Heterobilayer

  • PC Department Online Seminar
  • Date: Feb 23, 2021
  • Time: 04:00 PM (Local Time Germany)
  • Speaker: Dr. Xiu Lu
  • Tulane University, New Orleans, USA
Since the discovery of single photon emitters (SPEs) from monolayer WSe2 in 2015, the two-dimensional layered materials, including transition metal dichalcogenides (TMDCs) and hexagonal boron nitride (h-BN), has emerged to be a new playground for exploring quantum emitters and novel spin-photon interface1. A SPE in TMDC is believed to arise from trapping of an exciton by defects, localized strain or moirépotential which occurs in heterobilayer or twisted homobilayer. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

ZnO: Ultrafast photodoping

  • PC Online Talk
  • Date: Feb 18, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Lukas Gierster
  • FHI Department PC
Band bending at oxide surfaces induced by chemical doping or electric fields is known to create metallic surfaces with properties not found in the bulk, such as high electron mobility, magnetism or superconductivity. In this talk I show that photoexcitation of the ZnO(10-10) surface acts in direct analogy with chemical doping and induces band bending on ultrashort timescales. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Reaching for the stars with density functional theory

Accurately modeling warm dense matter deep inside astrophysical objects is a grand challenge.The associated thermodynamic states are characterized by solid-state densities, temperatures ofthousands of Kelvin, and GPa pressures. The extreme of the conditions can vary gravely dependingon the mass, radius, and composition of the studied object ranging from several GPa in planetarymantles to millions of GPa at the center of stellar interiors. A method that has proven highlysuccessful in describing this peculiar state of matter is density functional theory moleculardynamics (DFT-MD). [more]

Sum Frequency Microscopy of Phonon Polaritons

  • PC Online Talk
  • Date: Feb 11, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Sören Waßerroth
  • FHI Department PC
Sum frequency generation (SFG) allows the study of surfaces and inversion broken systems. In a new approach we implemented a wide field sum-frequency microscope combining the FHI infrared free electron laser (IR FEL) as excitation source with visible upconversion. The IR FEL provides a powerful, narrow band, and tunable light source [1]. By direct imaging of the SFG light with a microscope in a wide field scheme without scanning the sample or the focus [2], we achieve a spatial resolution well beyond the infrared diffraction limit. [more]

Automatic topography of multidimensional probability densities

A Seminar of the NOMAD Laboratory
Unsupervised methods in data analysis aim at obtaining a synthetic description of high-dimensional data landscapes, revealing their structure and their salient features. We will describe an approach for charting complex and heterogeneous data spaces, providing a topography of the high-dimensional probability density from which the data are harvested. [more]

Vibrational Surface Spectroscopy of Liquid, Interfaces with Nanometer Depth Resolution

  • PC Online Talk
  • Date: Jan 28, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Martin Thämer
  • FHI Department PC
An important portion of chemical reactions in biology, heterogeneous catalysis, or electrochemistry exclusively happens at liquid interfaces. This selectivity originates from the special physical and chemical properties of these interfaces, which can largely deviate from the corresponding bulk properties. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Ultrafast Electron Microscopy and Diffraction

  • PC Department Online Seminar
  • Date: Jan 25, 2021
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Prof. Jonas Weissenrieder
  • KTH Royal Institute of Technology, Stockholm
Ultrafast electron microscopy (UEM) facilitates microscopic imaging, diffraction, and spectroscopy at picosecond timescales. Electron probe bunches are generated through photoemission by a femtosecond UV laser pulse while a synchronized laser pulse excites a change of state in a sample of choice. I will show the design of the recently constructed UEM at KTH and some results from first model systems using both diffraction and imaging. [more]

Introduction to Approximate Bayesian Computation

The goal of statistical inference is to draw conclusions about properties of a population given a finite observed sample. This typically proceeds by first specifying a parametric statistical model (that identifies a likelihood function) for the data generating process which is indexed by parameters that need to be calibrated (estimated). There is always a trade-off between model simplicity / inferencial effort / prediction power. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Topology, Molecular Simulation, and Machine Learning as Routes to Exploring Structure and Phase Behavior in Molecular and Atomic Crystals

Organic molecular crystals frequently exist in multiple forms known as polymorphs. Structural differences between crystal polymorphs can affect desired properties, such as bioavailability of active pharmaceutical formulations, lethality of pesticides, or electrical conductivity of organic semiconductors. [more]

Smart Sampling for Chemical Property Landscapes with BOSS

A Seminar of the NOMAD Laboratory
Atomistic structure search for organic/inorganic heterostructures is made complex by the many degrees of freedom and the need for accurate but costly density-functional theory (DFT) simulations. To accelerate and simplify structure determination in such heterogeneous functional materials, we developed the Bayesian Optimization Structure Search (BOSS) approach [1]. BOSS builds N-dimensional surrogate models for the energy or property landscapes to infer global optima. The models are iteratively refined by sequentially sampling DFT data points with high information content. The uncertainty-led exploration/exploitation sampling strategy delivers global minima with modest sampling, but also ensures visits to less favorable regions of phase space to gather information on rare events and energy barriers. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Tracking Singlet Fission in Momentum Space

  • PC Online Talk
  • Date: Dec 10, 2020
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Alexander Neef
  • FHI Department PC
In organic materials with strong exchange interactions, the S = 0 (singlet) exciton might have twice the energy of the S = 1 (triplet) exciton. This allows the spin-conserving fission of the optically prepared singlet to two dark antiparallel triplets. Due to the many-body nature of this process, consensus over the underlying mechanism is still lacking. Here, we use trARPES to resolve the transient states involved in singlet fission in pentacene and provide new insights into the microscopic and ultrafast processes governing it. [more]

Datasets, Workflows, Models and Active Learning to Accelerate Catalyst Discovery

Machine learning accelerated catalyst discovery efforts has seen much progress in the last few years. Datasets of computational calculations have improved, models to connect surface structure with electronic structure or adsorption energies have gotten more sophisticated, and active learning exploration strategies are becoming routine in discovery efforts. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Energy Conversion Pathways in Graphite from Attosecond Soft X-ray Spectroscopy

  • PC Department Online Seminar
  • Date: Nov 23, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Jens Biegert
  • ICFO, Barcelona, Spain
The conversion of light to fundamental excitations of matter is governed by the build-up of electronic coherences and their dephasing to excited quasiparticles due to scattering processes, which occur on atto- and femtosecond timescales. Disentangling the interplay of these mechanisms, and how they lead to a specific flow of energy inside a material, is extremely challenging since many of these effects occur on overlapping temporal scales. [more]

FHI Library Online Workshop: Information Resources & Open Access

This interactive online workshop will introduce available options for making your research outputs open access. Discover which publishing fees are paid centrally or by the FHI library and get practical tips on how to adopt open access practices in your research area. Furthermore, you will get an overview of useful search tools. More details on how to join the workshop will be announced by e-mail or contact the library team.

Second-Harmonic Phonon Spectroscopy Using an Infrared Free-Electron Laser

  • PC Online Talk
  • Date: Nov 19, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Christopher Winta
  • FHI Department PC
Nonlinear optical spectroscopy constitutes a powerful tool for the investigation of crystalline solids and their structure. Apart from improved sensitivity compared to linear techniques, it offers additional experimental degrees of freedom which can be used to selectively study different symmetry components of the detected signal. The mid-infrared spectral region is particularly interesting as it contains optical phonon resonances which themselves carry symmetry information. [more]

Vom Energie- zum Nachhaltigkeitsmanagement - Die Freie Universität auf dem Weg zur Klimaneutralität

Die Freie Universität Berlin betreibt im eigenen institutionellen Verantwortungsbereich bereits seit zwei Jahrzehnten aktiven Umwelt- und Klimaschutz. 2001 gründete sie ein betriebliches Energiemanagement und entwickelte diese Aktivitäten schrittweise weiter: vom zertifizierten Umweltmanagement zu einem holistisch ausgerichteten Nachhaltigkeitsmanagement. Im Dezember 2019 hat die Freie Universität Berlin als erste deutsche Hochschule den Klimanotstand erklärt. Dieser beinhaltet die Verpflichtung, Nachhaltigkeit und Klimaschutz bei allen Entscheidungen und Planungen zu berücksichtigen und die Universität bis 2025 klimaneutral zu gestalten. [more]

Reference Management Systems

This course explains what reference management systems (also known as bibliographic or citation management software) are, why they are useful for any kind of research, and what to look out for when considering the use of one of the numerous available bibliographic management applications. The two systems, EndNote and Mendeley, are demonstrated as examples. More details on how to join the workshop will be announced by e-mail or contact the library team.

Bright and Dark Excitons in 2D Semiconductors and Heterostructures

  • PC Department Online Seminar
  • Date: Nov 9, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Alexander Högele
  • Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität, München
Van der Waals crystals of transition metal dichalcogenide (TMD) semiconductors have evolved as an increasingly significant material platform for condensed matter research. They can be routinely exfoliated down to the monolayer limit or assembled into rationally designed vertical heterostructures. In response to optical excitations, both semiconductor systems host strongly bound excitons in various configurations of spin and valley degrees of freedom. [more]

Der Wert der Biodiversität - Konsequenzen & Praxis

Im 21. Jahrhundert sterben Tierarten um ein vielfaches schneller aus als vor Beginn der Industrialisierung. Der Grund: menschliche Aktivitäten. Wir befinden uns in einer Biodiversitätskrise. Doch was bedeutet Biodiversität eigentlich? Braucht der Mensch Biodiversiät? Und hat Biodiversität auch einen Eigenwert? Im Vortrag werde ich diese Fragen beantworten, über die Konsequenzen sprechen, die sich aus der Biodiversitätskrise ergeben und wie man sich wissenschaftlich damit auseinandersetzt. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Momentum-resolved Interlayer Charge and Energy Transfer in a Monolayer WSe2/Graphene Heterostructure

  • PC Online Talk
  • Date: Oct 29, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Shuo Dong
  • FHI Department PC
Atomically thin layered van der Waals (vdW) heterostructures feature exotic and emergent optoelectronic properties.[1] With growing interest in these novel quantum materials, the microscopic understanding of the fundamental interlayer coupling is of capital importance.[2] Here, using four-dimensional photoemission spectroscopy, we provide a layer- and momentum-resolved view on ultrafast interlayer electron and energy transfer across a monolayer (ML)-WSe2/graphene heterostructure. [more]

The Key Role of Lattice Anharmonicity for Heat and Charge Transport in Solids: Fundamental Concepts, Novel Methods, and Relevant Applications

A Joint Seminar of the NOMAD Laboratory and of the Ma group
Heat and charge transport play a key role in materials science and thus for many technological applications that are key to establish a sustainable energy economy and ecology. Examples include improving the fuel-efficiency of aeronautic turbines [1], for developing efficient thermoelectric devices able to recover useful voltage from otherwise wasted heat [2], and for designing novel battery materials for advancing e-mobility [3]. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Charge-carrier dynamics and optoelectronic properties of metal halide perovskites for solar cells

  • Online Seminar
  • Date: Oct 12, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Adam D. Wright
  • University of Oxford
Over the past decade, metal halide perovskites have become renowned for their rapidly improving performance as photovoltaic active layers. This success has however often outpaced understanding of the electronic processes occurring within these materials. In this talk, I will give an overview of my work on the factors influencing electron motion and recombination in a series of metal halide perovskites, ranging from the archetypal CH3NH3PbI3 to the double-perovskite Cs2AgBiBr6. Using a combination of optical spectroscopy with computational techniques, I have investigated electron-phonon coupling [1], trap-mediated recombination [2], halide segregation [3] and intrinsic quantum confinement [4] within these materials, developing quantitative models to explain these phenomena. [more]

Spectroscopic Signatures of Edge States in the Quantum Spin Hall System Bismuthene

  • PC Online Talk
  • Date: Oct 8, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Julian Maklar
  • FHI Department PC
Quantum spin Hall (QSH) systems are two-dimensional topological insulators with promising device applications due to dissipationless spin currents in their edges. However, most QSH systems realized so far have required cryogenic temperatures due to their small bulk gap sizes. A candidate for a high-temperature QSH material is Bismuthene, i.e., a monolayer of bismuth arranged in a honeycomb lattice on a silicon carbide substrate, which features a semiconducting band structure with an indirect band gap of 0.8 eV. [more]

ARES: A Real-Space Electronic Structure Calculation Method

A Joint Seminar of the NOMAD Laboratory and of the Ma group
[more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

Structural dynamics of singlet fission in pentacene single crystals

  • PC Online Talk
  • Date: Oct 1, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Hélène Seiler
  • FHI Department PC
Singlet fission in organic molecular semiconductors has attracted significant attention for its relevance in opto-electronic applications. It is known that molecular packing strongly impacts singlet fission properties, and the structural dynamics are thought to play an essential role as well. Yet to this day, a direct probe of the molecular motions involved in the singlet fission process has been lacking. Here we directly observe the structural dynamics accompanying the singlet fission process in single crystal pentacene using femtosecond electron diffraction. [more]

Mapping Ultrafast Chemical Reaction Dynamics with Femtosecond Time-Resolved Time-Domain Raman Spectroscopy

  • Online Seminar
  • Date: Sep 28, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Prof. Hikaru Kuramochi
  • Institute for Molecular Science, Japan
In ordinary Raman spectroscopy, the laser source illuminates the sample, and the scattered light is collected, dispersed, and detected by a multi-channel detector yielding a Raman spectrum directly in the frequency domain. On the other hand, it is also possible to obtain a Raman spectrum by observing coherent molecular vibrations directly in the time domain using ultrashort pulses. [more]

Wave-optical Properties and Spatial Resolution in Point-projection Microscopy and Holography

  • PC Online Talk
  • Date: Sep 24, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Dr. Faruk Krecinic
  • FHI Department PC
Point-projection microscopy is an electron microscopy technique that uses a sharp metallic tip as a point source of electrons to project a magnified image of a sample, without any additional electron-optical lens elements. At sufficiently large magnification the projected image becomes an in-line hologram, which can be inverted to retrieve a real-space image of the sample object. Due to the use of low-energy electrons (typically <200 eV) this technique was shown to be capable of imaging a single elementary charge adsorbed on graphene, making it a sensitive probe of electric fields at the nanometer scale [1]. Moreover, photo-emitting the imaging electrons with an ultrafast pulsed laser enables the extension of PPM to the femtosecond domain, where it has demonstrated it can visualize the ultrafast dynamics of charge carriers with a combined spatial and temporal resolution of better than 100 nm and 30 fs, respectively [2,3]. [more]

What you get for free with Euclidean Neural Networks

Equivariance to Euclidean symmetry is a simple assumption with many consequences. In this talk, we show that Euclidean symmetry equivariant Neural Networks naturally inherit these consequences. [more]

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

FHI Library Online Workshop: Databases

Our interactive online workshop will help you to select and apply the most appropriate resources and tools for your research. Learn more on how to quickly find and analyze relevant scientific literature. The two databases Web of Science and SciFinder will be presented and discussed in detail. More details on how to join the workshop will be announced by e-mail or contact the library team.

The Evolution of Off-axis Electron Holography towards a Versatile TEM-Method

  • AC/PC Joint Seminar
  • Date: Sep 7, 2020
  • Time: 11:00 AM (Local Time Germany)
  • Speaker: Michael Lehmann
  • TU-Berlin Institut für Optik und Atomare Physik Electron Microscopy and -Holography
According to the original proposal by Dennis Gabor, electron holography was invented to overcome the electron-optical aberrations in the transmission electron microscope (TEM) by a-posteriori light optical correction. In order to fulfill Gabor’s dream, it took many decades and important developments like e.g. coherent electron sources, stable microscopes and rooms, fast CCD-cameras as well as dedicated computer software for reconstruction and correction. Nowadays with hardware aberration correctors, however, atomic resolution electron holography with a-posteriori correction of aberrations plays a less significant role. Meanwhile, the phase of the electron wave as carrier of information of electric potentials and/or magnetic fields in or around samples comes into focus for real-world applications pushing the development off-axis electron holography towards a method for measurements of these quantities on the nanometer scale. An interesting alternative electron-optical setup is dark-field off-axis electron holography for measurements of strain fields in solids. More recently, gating the interference fringe contrast by deliberately introducing of noise has open new developments towards time-resolved electron holography with a time-resolution in the nanosecond range. The talk will cover this evolution of electron holography up to the latest developments. [more]

Ultrafast Optical and Low-frequency Spectroscopy of Semiconductor Nano-systems and Quantum Materials

  • Online Seminar
  • Date: Aug 18, 2020
  • Time: 10:00 AM (Local Time Germany)
  • Speaker: Jit Sarkar
  • Indian Institute of Science Education and Research Kolkata
Ultrafast spectroscopic studies are always instructive to understand the physics of light-matter interactions. Within a few pico-seconds after photo-excitation, the excess energy of photo-excited carriers get transferred to the lattice and eventually they attain a state of equilibrium, a process known as ultrafast thermalization. Electron-phonon (e-ph) coupling play a pivotal role in this process. The process of ultrafast thermalization was investigated in an assembly of ZnO nanorods and the analysis from the framework of Two Temperature Model (TTM) yields prolonged thermalization time due to reduced electron-phonon coupling at higher photo-excited carrier density [1]. [more]

Triggering and Watching Water Electrolysis on Ultrafast Timescales

  • PC Online Talk
  • Date: Aug 13, 2020
  • Time: 03:00 PM (Local Time Germany)
  • Speaker: Gregor Zwaschka
  • FHI Department PC
For a greenhouse gas emission free society, hydrogen from water electrolysis is fundamental. Despite decades of study, the mechanism of the hydrogen evolution reaction (HER) on the best available catalyst, Pt, remains controversial. At least in part, understanding is complicated by not being able to disentangle the involved timescales ranging from femtoseconds (interfacial charge transfer) to milliseconds (mass transport).I approach this problem by performing perturbation experiments with ultrashort laser pulses that drive the HER close to its reversible potential and induce charge transfer along the Pt-H bond in the underpotential deposition region [1]. I disentangle the involved timescales by performing both i) time averaging electrochemical measurements under femtosecond laser irradiation and ii) time resolved sum frequency generation spectroscopy (SFS) of Pt-H after laser excitation.Ultrafast charge transfer is found to be a function of interfacial structure (electrode and electrolyte) and trends on single crystals and a microelectrode correlate with HER activity and allow insight into the reactions rate determining step. SFS provides information on Pt-H as a function of potential, electrolyte composition and temporal evolution during and after ultrafast charge transfer. Implications for the HER are discussed.[1] ChemElectroChem 2019, 6, 2675-2682 [more]
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