On-site Trainings (14th - 17th April, 2025)

TD-DFT simulations of K-edge resonant inelastic X-ray scattering

Vinícius Vaz da Cruz, Sebastian Eckert

In this exercise, you will be exposed to the basic concepts of molecular modeling and ab initio interpretation of experimental data. The tutorial ranges from molecular geometry optimizations, orbital visualization to spectral calculations, focusing on the resonant inelastic X-ray scattering process (RIXS). The tasks will focus on applying simulations of molecular electronic structure using Density Functional Theory (DFT) and its time dependent extension (TD-DFT) to access excited electronic states. We will investigate both occupied and unoccupied molecular orbitals that define bonding in molecular systems and discuss how they are probed within RIXS and how modeling allows drawing deeper insight from the measured spectra. The simulations will be carried out using the Orca quantum chemistry package for electronic structure calculations and Avogadro and Molden will be used for visualization of the results.

Accessing deeply buried interfaces via Hard X-ray Photoelectron Spectroscopy

Roberto Félix Duarte, Marcus Bär

The complexity of energy conversion devices, which often comprise a multitude of layers, interfaces, surfaces, elements, impurities, etc., dictates that it is of crucial importance to characterize and understand the chemical and electronic structure of each component both individually and as part of the larger system. In this module, students will get an introduction to hard x-ray photoelectron spectroscopy (HAXPES), an extraordinarily powerful method to determine the chemical and electronic characteristics of buried interfaces. By employing a range of excitation energies, the probing depth of the HAXPES measurements can be tuned to focus on the very surface of a sample or deeper into its near-surface region. This approach will serve as a straightforward way to carry out elemental depth profile analyses of an initially (i.e., at room temperature) inert heterointerface (i.e., “Material 1”/“Material 2”), an efficient alternative to measuring a sample series with different “Material 1” layer thicknesses. Furthermore, the reactivity of the investigated heterointerface as a function of sample temperature will be assessed by monitoring various element intermixing during in situ annealing treatment. The impact of thermally-induced diffusion mechanisms on the electronic interface structure will also be explored. This proposed course of action provides a more comprehensive picture than characterizing the chemical and electronic structure of sample series treated ex situ by different annealing temperatures. The experiments will be conducted at the High Kinetic Energy Photoelectron Spectrometer (HiKE) endstation located at the KMC-1 beamline of the BESSY II light source.

Revealing band structures of 2D materials using Angle-resolved photoemission (ARPES)

Alexander Fedorov, Maxim Krivenkov

Two-dimensional (2D) materials, such as graphene and its analogues (silicene, germanene, phosphorene, etc.) have attracted enormous research interest because of their outstanding electrical properties and potential applications for next-generation electronic devices. Angle-resolved photoemission spectroscopy (ARPES) is one of the most informative methods to study these systems, as it provides a direct view on the electronic band structure of materials, giving insights into their electronic properties. In this training, you will learn how to perform ARPES experiment with focus on 2D materials and how to do the basic analysis of ARPES data and interpret it. We will also explore how tuning synchrotron radiation parameters can reveal richer information about the materials under study.

Exfoliation and X-ray spectromicroscopy of 2D materials

Alevtina Smekhova, Florian Kronast

Atomically thin two-dimensional (2D) materials demonstrate intriguing physical, chemical, optical, electronic and magnetic properties, and are currently considered as promising candidates for the key blocks in the next-generation quantum and optoelectronic devices. Nowadays, many 2D materials can be organized in various vertically stacked van der Waals (vdW) heterostructures with the macroscopic lateral dimensions and stabilized against environmental degradation by different capping layers. In the future, these materials would allow substantial miniaturization of modern electronic devices along with significant expansion in their functionalities. In our training we invite participants to prepare 2D materials by mechanical exfoliation of vdW crystals in air with a possible assembly of a vdW heterostructure. The prepared 2D samples will be first evaluated by optical and eventually atomic-force microscopy, and then room-temperature electronic properties of particular configurations will be investigated by X-ray Photoemission Electron Microscopy (XPEEM) using element-specific X-ray techniques like XAS, XPS, and micro-ARPES. The stability of the prepared 2D samples and changes at their surfaces under heating can be checked in addition.

Tomoscopy: Time-resolved 3D imaging

Paul Kamm, Francisco Garcia-Moreno

Tomoscopy is a technique for the continuous and time-resolved in-situ and in-operando investigation of dynamic processes in various fields of research (biology, energy, materials science, etc.) in three spatial dimensions. The high flux of modern synchrotron (or liquid metal lab) X-ray sources and achieved sensitivities of new detectors allow a fast image acquisition rate, which in combination with the rotation of the investigated sample and the manipulation of the environment (temperature, pressure, atmosphere, etc.) allows tomographic imaging throughout the process. In this training, you will visualize how a time-resolved imaging experiment to investigate material scientific questions can be done. We will go through the processing of the collected data to reconstruct them and extract quantitative information, gaining understanding of the observed process.

More about the technique can be found in: X-ray Tomography and Tomoscopy on Metals: A Review (2023) Advanced Engineering Materials 2023, 25, 2201355; Tomoscopy: Time-Resolved Tomography for Dynamic Processes in Materials (2021) Advanced Materials 2021, 33, 2104659.

Multiple Energy Anomalous X-ray Diffraction (MEAD) on quaternary semiconductors

Daniel Többens

In this experiment, for example Kesterite‐type Cu₂ZnSnS₄ and Stannite‐type Cu₂FeSnS₄ will be investigated by Multiple Energy Anomalous X‐ray Diffraction (MEAD). For these spectra over the X‐ray absorption edges of Cu (8979 eV) and Zn (9659 eV) will be acquired at the KMC-2 Diffraction station (or MySpot beamline). The energy dependence of intensity corresponding to Bragg peaks 011 and 110 shows very distinctive differences depending on the distribution of copper and zinc. This allows clear and immediate distinction between kesterite‐type (real) and stannite‐type (once speculated, but disproved) crystal structure. Distinction between ordered and disordered Cu₂ZnSnS₄ is less obvious and ambiguous in this experiment, demonstrating also the limitations of this technique.

Monitoring buried interface formation using in-system laboratory- and synchrotron-based photoelectron spectroscopy

Johannes Frisch, Regan Wilks, Marcus Bär

The interfaces formed in multilayer thin films are the key to their functionality, and characterizing them in nondestructive manners is an area of great interest. The SISSY lab at the Energy Materials In-situ Laboratory Berlin (EMIL) features an advanced surface-sensitive characterization system which is connected via ultra-high vacuum transfer to deposition chambers. Avoiding exposure to ambient conditions helps guarantee that deposition of a film can be interrupted and restarted at various times with only a small influence on the final film composition. This experiment will involve stepwise, in-vacuum deposition of thin films combined with a series of surface sensitive x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy measurements. XPS measurements will describe film thickness, layer closure, chemical structure, and shifts in energy levels as the interface is formed. UPS measurements of the valence band maximum position and work function will complete the study of the electronic levels. The set of measurements will allow a complete picture of the energy level alignment at the interface to be built up and used to understand the behavior of the resulting device.

XANES in Standing Wave Geometry to study a W/Si layered interface

Ivo Zizak

An interface between the W and Si Layer will be studied at the MySpot beamline. The W layer is embedded into a waveguide between Au and Mo layers, with a Si spacer. The exact structure is shown in the figure. XANES spectra will be collected for different distributions of the electric field, demonstrating the depth sensitivity. From the 2.2 nm thick W layer, comparison is done between the spectra measured in the middle of the layer (metallic W) and at the interface to Si. In this experiment, we will first measure the reflectometry and fluorescence from the sample. Evaluation of these spectra will help to estimate the distribution of the X‐ray in depth of the sample. Results will be compared to a simulation and differences will be discussed.  Two geometries are selected: i) X‐ray intensity is concentrated in the middle of the layer, giving pure metallic W spectrum,  and ii) maximal intensity is at the interface between W and Si, giving spectrum specific for WSi alloy. According to the results of the first part, we will be able to set the parameters for an XANES experiment. Dependency between the electric field pattern and wavelength, as well as the necessary angle correction will be discussed. The data will be loaded and viewed using Athena software suite. Provided literature will be used to be compared with the results.

Resonant Inelastic X-ray Scattering (RIXS)

Maximilian Kusch

Low energy excitations in functional materials are important to reveal their intrinsic properties. In this experiment, we are going to use photon-in-photon-out technique at EUV and soft-x-ray regions (30-270 eV range) to unveil the bandgap in lanthanum-containing insulators [1]. The participants will learn from sample preparation, code-based measuring techniques to data analysis. The solid samples will be probed by X-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), which will be conducted at the dedicated meV-RIXS experimental station [2]. The high-resolution setup serves as a powerful tool to unambiguously determine the electronic transition and its coupled degree of freedom [3]. With the precise determination of the peak position, we will use the atomic 5p-4f transition as a local atomic sensor. Based on the chemical shift observed, we will see how this valence transition is perturbed by the band(gap) formation and determine the bandgap of the unknown samples by the established linear regression.

[1] C.-Y. Liu et al., manuscript submitted to Advanced Materials; [2] K. Bauer et al., J. Synchrotron Radiat. 29, 1 (2022); [3] C.-Y. Liu et al., Phys. Rev. B 106, 035104 (2022).

At-wavelength characterization of XUV diffraction gratings

Andrey Sokolov and Analía Fernández Herrero

As far as optical constants of materials forming reflected/scattered radiation have significant impact on optical elements performance the final examination can be done only directly at dedicated working wavelength / photon energy range. An experiment by measuring diffraction grating efficiency in its working energy rage will be carried out. Measured efficiency will be compared with calculated one based on the grating profile parameters extracted from AFM scans on the sample surface. During experimental data processing some additional grating parameters will be extracted: line density, scattering level, surface curvature, top coating quality (chemical compound, roughness, contamination).

MX beamlines

Manfred S. Weiss, Uwe Mueller, Frank Lennartz, Tatjana Barthel

We will prepare crystals of the sweet protein thaumatin beforehand. During the practical (3 hours), the students will prepare the crystals for the diffraction experiment, by mounting them in a nylon loop and immersing them in LN2. A diffraction experiment will be carried out at one of the MX beamlines. The data will be processed and the structure determined by molecular replacement. A small molecule binding to the surface of thaumatin will be identified by difference density analysis.

Investigation of different nanostructured samples using Small-Angle X-ray Scattering

Eneli Monerjan, Armin Hoell

An ASAXS and GISAXS instrument is set up by the HZB in collaboration with the National Metrology Institute of Germany, PTB. Small-Angle X-ray Scattering (SAXS) is a powerful method to investigate nanostructures within a broad range of inorganic, organic, and biological materials. SAXS enables the determination of average structural parameters across a length scale ranging from slightly above atomic dimensions to approximately 100 nanometers in complex, multicomponent systems, including amorphous materials. These structural parameters encompass sizes, size distributions, volume fractions, and inner surface dimensions. In this training you will learn the essential steps for conducting a SAXS experiment, how to mount samples, understand the beamline and instrumental setup, and explore the different cycles required to execute the experiment. The acquired data will be processed and interpreted using instrument-specific and freely accessible software tools.

3D/4D hard X-ray Imaging of Batteries 

Ralf F. Ziesche, Henning Markötter

In recent years, Li-ion batteries and their potential successors have become one of the most important energy storage devices for portable technology such as mobile phones and electric cars. However, the real available gravimetric/volumetric energy density and rate performance are still far from the theoretical ones. Multi-dimensional characterisation techniques are the key to a deep understanding of battery operation and performance. Hard X-ray imaging provides valuable information about the 3D morphological changes during discharge/charge in ex-situ and operando with spatial resolution below 1 µm. During the training we will give you an insight into the work with the hard X-ray imaging instrument BAMline during the investigation of Li-ion batteries. We will train you in the basics of battery cycling, ex-situ/operando hard X-ray imaging, tomography reconstruction and data analysis.

Investigation of magnetic materials for spintronics by X-ray magnetic circular dichroism at VEKMAG

Florin Radu

Magnetic switching is in hard disc drives performed by magnetic fields but in the future energy-efficient information technology, magnetic fields are avoided. One possibility is all optical switching using polarized light. The materials investigated for all optical switching are mostly ferrimagnetic compounds of rare earths and transition metals. While conventional magnetometry cannot distinguish between the magnetic contributions of the individual constituents in terms of magnetic moments and even their sign, the method of x-ray magnetic circular dichroism (XMCD) in absorption is element specific. This means the absorption lines in the photon energy range of 500 – 1500 eV are investigated with circularly polarized light. The innovative VEKMAG instrument features a vector magnet with up to 9 T along the direction parallel to the photon beam and 1 T in any direction is perfectly suited for such investigations. Depending on the applied magnetic field and the sample temperature, the magnetic moments of different constituents are aligned and their XMCD signal investigated. In this experiment, the participants will produce samples of typical ferrimagnetic compounds such as Fe-Tb and Co-Dy in a setup for thin film growth by sputtering. Subsequently, they will transfer the samples and perform XMCD experiments. In the data analysis, we will analyze the spectra with the help of the so-called sum rules and determine the orbital and spin magnetic moments of the 3d and the 4f magnetic sublattices.

Machine learning prediction of spectra with molecular graphs 

Annika Bande

Machine learning (ML) gains more importance in chemistry and may become a replacement to other computational methods such as density-functional theory. In this exercise, the participants will be exposed to some basic concepts of predicting chemical properties (e. g. X-ray spectra) with ML. The exercise will involve a gentle introduction to the types of tasks in machine learning, and a general idea of how ML algorithms work. We will then define the problem of predicting spectra with ML in detail. This will then be followed by a brief discussion and basic introduction to molecular representations such as SMILES, Coulomb matrices and graphs using python. The session will then have a discussion of the message passing on graph neural networks. The hands-on task will be training a small GNN framework that predicts spectra or other molecular properties.

Charge Density Waves in a TaS₂ surface investigated by photoelectron spectroscopy 

Nomi Sorgenfrei, Johannes Lütgert

Photoelectron Spectrsocopy (PES) is a powerful tool to investigate the chemical surrounding of different atoms. Not only is PES element-specific but also sensitive to variations of the electronic surrounding of the different species due to the crystal field. This technique is called Electron Spectroscopy for Chemical Analysis or ESCA.
TaS₂ is a particular interesting material for this class of experiments, since it exhibits a charge density wave (CDW) which modulates the electronic surroundings of the Tantalum atoms and is reflected in the photoelectron spectrum. During the photon school, you will prepare a TaS₂ sample for measurement, characterize it and investigate the phase transitions induced by cooling the sample with liquid nitrogen. You will also analyse the data, learn how to use fitting routines and prepare a short presentation.

Photochemistry in Liquids – Time-resolved and steady-state soft X-ray absorption 

Mattis Fondell & Leo Cordsmeier

The AXSYS-nmTransmission Near-edge X-ray absorption fine structure (NEXAFS) station is dedicated to time-resolved and steady-state soft x-ray absorption spectroscopy on liquid samples that are continuously refreshed in a flat jet system. Applications include: photo-induced ligand substitution, proton transfer - systematic investigations, electronic structure changes upon UV excitation, detection of excited states by photo-absorption. In this example, NEXAFS at the nitrogen K-edge served as the probe of the chemical state. By monitoring the electronic and solvation structures as a function of the protonation state and the O– substitution position on the pyridine ring, the amplification of the isomeric differences in aqueous solution can be investigated.