Öffnet in neuem Fenster Opens in a new window Öffnet externe Seite Opens an external site Öffnet externe Seite in neuem Fenster Opens an external site in a new window

Photon School

Online Trainings

This is a list of the online trainings taking place 11th April – 14th April 2022, contingent on BESSY II is operating at a level that allows HZB employees access.

Please choose up your first and second choice of training.

Training_01: TD-DFT simulations of K-edge resonant inelastic X-ray scattering (Vinicius 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.

Training_02: 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.

Training_03: Revealing band structures of 2D materials using Angle-resolved photoemission (ARPES) (Maryam Sajedi, 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. Particularly, Blue phosphorene (BlueP) is a unique 2D phosphorus allotrope with wide semiconducting band gap highly relevant for optoelectronic applications. 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 seminar, you will learn how to do the basic analysis of modern ARPES data and interpret it. For this, we will work on ARPES results of some 2D systems, and show how synchrotron radiation can be exploited to obtain richer information.

Training_04: Basic and advanced analysis of extended X-ray absorption fine structure data (Janis Timoshenko)

X-ray absorption spectroscopy (XAS), and, in particular, analysis of extended X-ray absorption fine structure (EXAFS) is a powerful approach for determination of local structure (coordination numbers, bond lengths, disorder around X-rays absorbing atoms) in a broad range of materials and in a broad range of experimental conditions. An important advantage of EXAFS spectroscopy is that the spectra can be easily simulated, thus enabling accurate quantitative analysis of materials structure. In practice, however, caution is needed when performing quantitative EXAFS interpretation, because the relationship between EXAFS features in experimental data and material’s structure is often non-trivial. Here we introduce the conventional approach for EXAFS analysis based on non-linear least-squares fitting, and use it for interpretation of EXAFS spectra in simple crystalline materials. Next, the limitations of the conventional approach are demonstrated, in particular, in studies of strongly disordered materials and in the interpretation of EXAFS contributions from distant neighbors. Advanced fitting approach based on reverse Monte Carlo simulations is explained and used to overcome them.  At the end of the activity, participants are expected to gain practical skills in EXAFS data analysis using codes FEFF (for EXAFS modeling), Demeter (for EXAFS processing and fitting) and EvAX (for reverse Monte Carlo modeling).

Training_05: Tomoscopy: Time-resolved 3D imaging (Paul Kamm)

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 communications10(1), 1-9 and García-Moreno, et al. J. Synchrotron Radiat. 25 (2018)

Training_06: Multiple Energy Anomalous X‐ray Diffraction (MEAD) on quaternary semiconductors (Daniel Többens)

In this experiment, for example Kesterite‐type Cu2ZnSnS4 and Stannite‐type Cu2FeSnS4will be intestigated 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.

Training_07: 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.

Training_08: 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 (or KMC-2). 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, 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 measured data will be loaded and viewed using “Athena” software suite. Provided literature will be used to be compared with the results.

Training_09: Gas-Phase X-ray absorption spectroscopy in ion yield mode (Vicente Zamudio-Bayer)

By using a cryogenically cooled, high-capacity ion trap, we are able to perform near-edge x-ray absorption spectroscopy (NEXAFS) on extremely dilute gas-phase samples which only weakly interact with the environment. With this approach, the intrinsic electronic structure of highly reactive and/or unstable ions is studied. With the help of electrostatic lenses and radio-frequency ion guides, we have control of the sample composition at the atomic level. Available samples range from simple few atom molecules relevant for astrophysics, to metal-centered coordination complexes, to pure and doped nanoclusters. In this on-line training we will show you the sample preparation, how measurements are done and preliminary analysis via mass spectrometry, and x-ray ion-yield spectroscopy.

Training_10: At-wavelength characterization of XUV diffraction gratings (Andrey Sokolov)

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).

Training_11: MX beamlines (Tatjana Barthel, Frank Lennartz and Gert Weber)

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.

Training_12: MAXYMUS (MAgnetic X-raY Microscope with UHV Spectroscopy) (Markus Weigand, Sebastian Wintz)

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.

Training_13: 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 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.

Training_14: Machine learning prediction of spectra with molecular graphs (Thorren Kirschbaum, Kanishka Singh)

Machine learning (ML) gains more importance in chemistry and may become a replacement to other computational methods 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 in graph neural networks. The hands-on task will be the training a small GNN framework that predicts spectra or other molecular properties.

Training_15: Generation of attosecond pulses in the extreme ultraviolet (Tobias Witting, Federico Furch)

Laboratory-size coherent light sources based on high-order harmonic generation from optical lasers offer an alternative to synchrotron radiation when extreme temporal resolution is required. These compact sources produce light pulses with attosecond duration (1as = 10-18s) and allow studying electron dynamics on its natural timescale. In this exercise we will use numerical simulations to review the most widespread route to produce attosecond pulses in the extreme ultraviolet (XUV) utilizing commercial lasers delivering femtosecond (1fs=10-15s) laser pulses in the near infrared. We will review the basic properties of linear propagation of ultrashort laser pulses and simulate nonlinear propagation conditions leading to the formation of laser pulses lasting only a few optical cycles. Then, we will simulate the generation of extreme ultraviolet radiation by means of high-order harmonic generation driven by the few-cycle laser pulses. Next, we will explore methods to isolate a single XUV pulse and simulate the results of an attosecond electron streaking experiment. Attosecond electron streaking is one of the methods utilized to explore electron dynamics. It can also be used to characterize the attosecond pulses.

Image: top) part of the high repetition rate attosecond beamline at MBI, bottom: Attosecond electron streaking trace.