Trainings

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.

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.

At BESSY II, a unique Angle-resolved Time of Flight (ArTOF) electron spectroctroscopy has been developed to determine the electronic structure of functional materials with the lowest possible synchrotron light dose, in order to characterize materials in their undisturbed, "native" state. In particular, this Electron Spectroscopy for Chemical Analysis (ESCA) at low Dose is employed to yield the atomic composition of functional and the chemical and physical changes they undergo. This allows us to follow charge separation in photovoltaic absorbers or phase transitions in solid state switching and sensing materials on a fundamental level, such as the 3D representation of the valence band of graphene. Further info can be found in: https://doi.org/10.1016/j.elspec.2017.05.011 or LowDosePES end-station at PM4 beamline.

Magnetic skyrmions are vortex-like configurations occurring in particular bulk or thin film samples. Due to a non-trivial magnetic topology skyrmions are very stable, i.e. a high energy barrier needs to be overcome to reverse or reset their magnetization, making them interesting systems for magnetic data storage. In this experiment we will use the photoemission electron microscope (PEEM) to investigate the formation and annihilation of magnetic skyrmions in a bilayer of the amorphous ferromagnet CoFeB and the heavy metal Pt. Controlled formation of skyrmions is a key issue for the functionality of any device based on skyrmions. The experiment will consist of two parts. First we will study the formation and fluctuation of skyrmions as function of an external magnetic field and temperature. Above a certain temperature threshold thermal fluctuations are expected causing spontaneous skyrmion formation. Thereafter we will keep the sample temperature well below the threshold of spontaneous skyrmion formation and use a single laser pulse of 60fs duration to create or annihilate individual skyrmions. Knowing the parameters of the laser pulse such as pulse energy duration and polarization will allow us to simulate the time-evolution of the local temperature profile and disentangle mechanisms such as local heating or laser helicity driven magnetization switching that have been suggested to govern the laser induced skyrmion formation process.

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 García-Moreno, F., Kamm, P. H., et al. (2019). Using X-ray tomoscopy to explore the dynamics of foaming metal. Nature communications, 10(1), 1-9 and García-Moreno, et al. J. Synchrotron Radiat. 25 (2018)

In this experiment, for example Kesterite‐type Cu₂ZnSnS₄ and Stannite‐type Cu₂FeSnS₄will be investigated by Multiple Energy Anomalous X‐ray Diffraction (MEAD). For this 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.  

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.

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 technique 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 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).

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 of 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).

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.

The Physikalisch-Technische Bundesanstalt (PTB), the German National Metrology Institute, operates a unique metrology laboratory at BESSY II.  Different X-ray based metrology techniques are conducted at various dipole and undulator beamlines with multiple and flexible endstations. Within this experiment two different techniques at two different endstations will be used to characterize nanolayer systems. Grazing incidence X-ray fluorescence analysis (GIXRF) and X-ray reflectometry (XRR) are applied to determine different structures form simple layers to 3D nanostructures. The PTB measurement systems also enable a traceable quantification of the nanolayers thickness or amount of material by also quantifying the different elements within the sample system. These measurement principles are of importance for applications in the semiconductor industry and many other fields of application.

MAXYMUS is a scanning transmission x-ray microscope and a fixed endstation of the UE46-PGM2 undulator beamline. MAXYMUS operates by focusing a coherent x-ray beam to nanometer-sized spots which are scanned across sample. To probe the local x-ray absorption, light passing through the sample is measured for each point by a variety of available x-ray detectors including photomultiplier, avalanche diode or in-vacuum CCD camera. This allows to use x-ray spectroscopic techniques as contrast mechanism, making it possible to do element specific, chemically and magnetically sensitive imaging with resolutions below 20 nm. MAXYMUS endstation allows users to utilize X-ray magnetic circular dichroism (XMCD) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy contrast mechanisms both for imaging and for nano-spectroscopy of samples, in the energy range between 150 and 1900 eV and on sub 30nm length scales. Samples can be transparent (the classical mode) as well as bulk, with imaging being done by sample current measurement (TEY - total electron yield). The experiment will be the imaging of one or more samples of the current beamline user and the analysis of the obtained images. The required imaging mode for the respective samples will be selected as well as the required sample environment.

Magnetic switching is in hard disc drives performed by magnetic fields but in a 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, they will analyze the spectra with the help of so-called sum rules and determine the orbital and spin magnetic moments of the 3d and the 4f magnetic sublattices.

CoESCA is equipped with two Angle-Resolved Time-Of-Flight spectrometers to measure the 3D angular resolved electron distributions, either independently or in coincidence mode. Shot-to-shot data saving for each of the spectrometers allows for investigating the time evolution of the data and post-processing on slow time scales from minutes to hours. The ArTOFs’ high information rate makes studies of radiation sensitive samples at very low photon flux feasible even in a reasonable acquisition time.