Hands-on trainings

This is a list of the synchrotron–based and laboratory-based experiments that are offered for the second week of the HZB Photon School. Please choose up to two experiments of your preference.  

Experiment_01: Chemical analysis in molecules (Annette Pietzsch)

In this experiment we will investigate dilute molecular systems using resonant inelastic x-ray scattering (RIXS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. By resonantly exciting the system with soft x-rays we can extract local information on the valence electronic structure at selected atomic centers. We investigate transition metal complexes as well as biologically relevant systems in their “natural” environment. The student will join one of our ongoing projects, participate in sample preparation and injection as well data taking and evaluate a selected data set. The EDAX@VSR endstation is dedicated to NEXAFS and RIXS experiments on liquid samples and gasses in the soft x-ray range. The liquids are injected into the chamber via a liquid jet system whereas gasses as well as small amounts of liquids can be investigated using a liquid/gas flow cell.  With this experimental setup, we explore the energy landscapes and dynamic pathways in molecular systems. We use RIXS as an atom specific and chemically selective probe to unravel the interplay of bonding and structure in molecular systems. Investigating on the respective atomic length and time scales, we work to unveil fundamental correlations of transient electronic structures and nuclear dynamics. Our goal is to gain a novel understanding of photochemical dissociation, protonation, charge transfer, and isomerisation reactions to ultimately develop new schemes for controlling chemical reactions. A detailed description of the setup is found in: A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources. K. Kunnus et al. Review of scientific instruments 83 (12), 123109 (2012)

Experiment_02: Resonant inelastic x-ray scattering (RIXS) at the L3 edge of NiO (Klaus Lieutenant, Christian Schulz)

In a RIXS process a photon is resonantly absorbed and re-emitted in a second order process that leaves the system in an excited state. The energy of this excitation corresponds to the energy difference between the incoming and outgoing photon energy. In this experiment we will study d-d and charge transfer excitations in NiO employing x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) at the endstation PEAXIS. After aligning the NiO crystal, subsequent XAS measurements will be performed to determine the relevant resonance energies in NiO for the foreseen RIXS studies. The setup for the RIXS spectrometer has to be optimized for these energies. After this crucial optimization, RIXS measurements at the resonance energies will clearly indicate inelastic x-ray scattering due to d-d excitations and charge transfer in NiO upon x-ray absorption and subsequent x-ray emission. An energy calibration will complement the measurements and facilitate data interpretation. During the allocated time, we will ideally be able to measure an entire set of RIXS spectra at different incident photon energies between the identified resonance energies, a so-called RIXS map. A result of the data analysis will be for instance a 2D plot from these individual measurements and a quantitative determination of the d-d splitting in NiO.

Experiment_03: Photoelectron Spectroscopy on Functional Materials (Erika Giangrisostomi, Ruslan Ovsyannikov)

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.

Experiment_04: Accessing deeply buried interfaces via Hard X-ray Photoelectron Spectroscopy (Roberto Félix Duarte, Regan Wilks, 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 participate in a hands-on introduction of hard x-ray photoelectron spectroscopy (HAXPES), an extraordinarily powerful method to determine the chemical and electronic characteristics of not only sample surfaces, but more usefully 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.


Experiment_05: 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.

Experiment_06: Multiple Energy Anomalous X‐ray Diffraction (MEAD) on Kesterite‐type Cu2ZnSnS4 and Stannite‐type Cu2FeSnS4 (Daniel Többens)

In this experiment, 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.

Experiment_07: Investigating high temperature superconductors by ARPES (Oliver Rader, Alexander Fedorov)

Angle-resolved photoelectron spectroscopy (ARPES) is the primary method for measuring the band structure of solids. The data give also information on the coupling of the electron to excitations such as phonons and magnons is The ARPES 1^3 endstation is a worldwide unique instruments because it allows ARPES measurements with synchrotron radiation at temperatures below 1 K.  Such low temperatures are important because they reduce thermal broadening and hence allow measurements at a smaller energy scale – in the present case of milli electron volts. Another reason is that they allow to reach ordered phases at low temperature such as superconductivity or ferromagnetism. In this experiment we will measure the band structure of a cuprate high Tc superconductors. The phase diagram of cuprate superconductors is complex as a function of temperature and hole-doping. The transition from a Fermi liquid phase to the superconducting phase can be observed and the formation of a band gap as signature of Cooper pair formation. So, we will explore parts of the phase space of a representative superconductor.

Experiment_08: Spin- and angle-resolved photoemission (spin-ARPES) of topological insulators (Oliver Rader, 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. As a consequence 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.

Experiment_09: Imaging and manipulating magnetic skyrmions by SPEEM (Florian Kronast, Sergio Valencia, Mohamad A. Mawass)

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.

Experiment_10: Investigation of magnetic materials for spintronics by X-ray magnetic circular dichroism at VEKMAG (Florin Radu, Radu Abrudan)

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.

Experiment_11: Electron spin couplings probed by coherent THz light by electron paramagnetic resonant (EPR)/THz-Spectroscopy (Karsten Holldack, Alexander Schnegg, Thomas Lohmiller)

In the user-experiment at the THz-EPR end-station students will be introduced to basic concepts of coherent synchrotron radiation in the THz range, quasi-optical THz-beam lines and the ultra-sensitive detection of THz radiation with liquid Helium cooled bolometers.  Furthermore, the participants will use a super-conducting high- field magnet and perform electron paramagnetic resonance experiments to study the properties of a single molecule magnet below liquid Helium temperatures.

Experiment_12: Hands-on experiments at the Infrared Microscopy Endstation of the IRIS Beamline (Ljiljana Puskar, Ulrich Schade)

An infrared microscope will be used to offer hands-on measurements with brilliant infrared synchrotron radiation. The aim of this experimental course is to provide the school attendees with a practical understanding of the concept of diffraction limited infrared microspectroscopy. By choosing appropriate series of apertures with sizes down to the wavelength of radiation the students will understand the advantage of synchrotron infrared light over conventional laboratory broadband sources. This experience will then be used to perform further experiments on the microscope using realistic samples such as cross sections of biological tissues and others.

Experiment_13: Real-time diffraction using a liquid metal-jet X-ray source (Roland Mainz, Tobias Scherb)

The in-situ X-ray Lab at Adlershof is dedicated to the study of reactive growth processes of functional thin films and the formation of crystalline phases during various types of solid state reactions by real-time X-ray diffraction. The laboratory is equipped with a novel high-flux X-ray setup which uses an X-ray source with a liquid metal-jet as anode. Whereas standard X-ray anodes have the limitation that they melt at too high excitation densities, this limit is shifted up to much higher densities by the use of a liquid anode. The high X-ray flux allows X-ray diffraction with a time resolutions that has only been possible at synchrotrons before. The instrument concept is modular to enable energy- and angular-dispersive diffraction modes with different sample environment.

In this experiment, we will perform annealing experiments to investigate the formation and evolution of phases depending on temperature and gas atmosphere in real time. For this, the X-rays are focused onto a sample placed inside a heating stage. Diffracted X-rays will be continuously recorded by a 2D-X-ray detector during heating. Subsequently, the data from the 2D detector will first be analysed to extract the evolution of the intensities to study the decay and formation of crystalline phases. A more detailed analysis of the shape of the diffraction signals may provide further insights into the reaction mechanisms during annealing.

Experiment_14: Monitoring buried interface formation using in-system laboratory-based photoelectron spectroscopy (Regan Wilks, Marcus Bär, Raül García Diez)

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.