On-site Trainings  (22 - 25 March, 2027)

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

Vinícius Vaz da Cruz, Wagner Ribeiro da Silva Neto

In this exercise, you will be exposed to the basic concepts of molecular modelling 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 modelling 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

Angelo Rillera, 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 Presto endstation located at the KMC-1 beamline.

X-ray sensitivity to orbital magnetism

Nele Thielemann

In the field of modern magnetism, the role of orbital angular momentum attracts increasing attention. The orbital state dictates the coupling of spins to their surroundings and is essential to form stable magnetic domains. Strong interest also emerges in the field of ultrafast magnetization dynamics, where ultrafast control of orbital states and orbitronic materials are currently discussed as potential routes towards energy efficient information technology. With soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) we can directly access magnetic moments in an element and state selective manner and can disentangle spin and orbital degrees of freedom with XMCD sum rule analyses. In the practical training at the PM3 beamline you will get hands-on experience with beamline control, sample transfer and alignment, XAS/XMCD experiments and learn about X-ray sensitivity to orbital degrees of freedom by studying different magnetic materials.

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 their characterisation in non-destructive 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 behaviour of the resulting device.

XANES in Standing Wave Geometry to study an interface between the W and Si Layer

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)

Katarzyna Siewierska, Marco Kliem

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., J. Phys. Chem. C 2023, 127, 23, 11111-11118. https://doi.org/10.1021/acs.jpcc.3c02011 

At-wavelength characterization of XUV diffraction gratings

Andrey Sokolov & 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 range 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).

Coincidence Electron Spectroscopy for Chemical Analysis CoESCA at UE52-PGM

Danilo Kühn, Erika Giangrisostomi, Johannes Lütgert

Exploring the electronic structure of solids and surfaces is of fundamental importance to understanding their physical properties such as magnetism, phase transitions, catalytic activity etc. Photoelectron Spectroscopy (PES) and Auger Electron Spectroscopy (AES) with synchrotron light are important and much used tools to study the electronic properties. PES can give information about elemental composition, chemical state of the elements and even about electron dynamics. AES, on the other hand, provides information about valence electronic structure, coupling of core-holes to other electron levels and electron interaction strengths. However, quantitative understanding of PES and AES is sometimes difficult, because of the overlapping of various photoemission lines and atomic multiplet structures, excitation satellites, electronic screening effects and lifetime broadening. We at COESCA use Auger Photo electron Coincidence Spectroscopy (APECS) to overcome these limitations and to explore electronic structure of solids and surfaces, like transition metal oxides or single crystal catalysts in detail. We use self-developed software tools based on python and IgorPro to analyze our big, multidimensional datasets.

Machine learning prediction of spectra with molecular graphs

Hendrik Junkawitsch, Eric May

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 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, Ben John

Photoelectron spectroscopy (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-nm Transmission 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.  The experiment provides the unique capability to probe electronic structure changes of molecules in solution through soft X-ray absorption on picosecond timescales subsequently to a laser excitation. This training will introduce liquid-jets. The participants will record X-ray absorption spectra of molecule in solution at the nitrogen K- and the iron L-edge. They will use a laser system to promote the molecule to a valence excited state and detect the characteristic X-ray absorption changes related to this excitation.

doi: 10.1021/acs.jpcb.0c10873

In Situ Growth and XPS/NEXAFS Studies of 2D Materials

Anna Makarova, Emile Rienks

Two-dimensional (2D) materials, such as hexagonal boron nitride (h-BN), graphene and its analogues (silicene, germanene, phosphorene, etc.), as well as their corresponding heterostructures, have attracted enormous research interest due to their unique structural, chemical, and electronic properties and their potential applications in next-generation technologies. Synchrotron-based X-ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy are powerful tools for investigating these systems, providing insights into their chemical composition, bonding configurations, orbital orientations, and electronic structure. In this training, you will learn how to perform soft X-ray photoemission and absorption experiments, with a focus on in situ-grown 2D materials. You will gain practical experience in chemical vapor deposition (CVD) growth, selecting experimental parameters, acquiring spectroscopic data, performing data analysis, and interpreting the results to understand the chemical and electronic properties of these materials.

Photoelectron Angular Distributions from Liquid Water

Robert Seidel, Andreas Siebert

When X-rays knock electrons out of water molecules, do they fly off equally in all directions, or are some directions preferred? In this hands-on training, you will explore how the emission direction depends on the electron's kinetic energy and the orbital it comes from.
Using the SOL³PES setup at the UE51-PGM-2 beamline at BESSY II, you will measure valence-band and core-level photoelectron spectra from a liquid-water microjet and surrounding water vapor at different X-ray energies and polarization angles.
You will actively participate in every step of the experiment: preparing the injection system, aligning the liquid microjet, refilling liquid-nitrogen cold traps, setting experimental conditions, and recording spectra. Finally, you will analyze your data using IGOR Pro, determine the photoelectron anisotropy parameter β, and discover how electron emission from liquid water differs from that of isolated water molecules in the gas phase.

Spin- and angle-resolved photoemission (spin-ARPES) of topological insulators

Jaime Sánchez Barriga

Topological insulators and semimetals feature surface states and surface Fermi arcs that are protected by topological properties of the respective material. These cannot be altered by weak disorder. Because of the topological properties the surface states bear a spin texture which can be measured by and angle-resolved photoemission (spin-ARPES). This spin texture is of particular interest in the framework of a future spintronics which may replace conventional charge-based electronics for information processing. While spin currents are in a certain sense ubiquitous, the generation of spin currents is not trivial. It has recently been shown that spin currents can be triggered in topological insulators by excitation with circularly polarized light. As the detection method, ARPES and spin-ARPES are used. The method can measure the occupied spin-dependent electronic band structure of crystalline solids. Several aspects govern the spin current generation, and the spin polarization of the electrons emitted in the photoemission process, and these depend on geometry, light polarization, photon energy etc. We will check in this experiment a particular theoretical prediction to decide between different explanations.