PETRA III Variable Polarization XUV Beamline P04 Users Meeting 2016

23 Feb 2016, 12:30 → 24 Feb 2016, 16:30 Europe/Berlin

FLASH seminar room in building 28c (DESY Hamburg)

Programme P04_users_meeting_2016_program.pdf

Tuesday 23 February

12:30 → 13:00 Registration

Registration

13:00 → 15:00 Status and progress reports

Status and progress reports

13:00 Welcome

oral

Speaker: Dr Oliver Seeck (DESY, FS-PE)

13:20 Report on beamline P04 at PETRA III

Overview report on beamline P04

Speaker: Dr Jens Viefhaus (DESY, FS-PE)

14:00 P04 beamline media, best practices and guidelines

Oral

Speaker: Mr Jörn Seltmann (DESY, FS-PE)

14:20 Future P04 beamline layout and P04 control GUI

Oral

Speaker: Mr Frank Scholz (DESY, FS-PE)

14:40 P04 Beamline communication, scaning, data storage and analysis

Oral

Speaker: Dr Gregor Hartmann (DESY, FS-PE)

15:00 → 15:30 Coffee break

Coffee break

15:30 → 17:00 User reports

User reports

15:30 Time-resolved pump-probe experiment at PO4 with synchrotron and laser

We combined narrow-bandwidth soft X-ray radiation, with an optical femtosecond laser (515nm, 2.4eV), to study the Auger cascade of core-excited atomic Ne in a time-resolved fashion. An X-ray pulse of 100ps duration and energy near 867eV stimulates the Ne1s->3p excitation. This core-excited state decays within its lifetime of ~2.4fs, almost instantaneous for every synchrotron and for most existing light sources. Most of the Ne1s-13p decays occur via emission of a fast Auger electron into a Ne+ ion, predominantly with 2 valence vacancies and one electron occupying a higher-lying valence orbital. These Ne+ products can undergo further Auger decay, emitting a “2nd-step” Auger electron in the energy range up to ~35eV. Unlike the almost instantaneous Auger decay of the core-excited state, the 2nd-step decay can occur on a very broad time-range spanning up to several ns. During this time interval we fire a laser pulse into the interaction region probed by the X-ray, and we monitor the Auger electron spectra for the 2nd step decay while scanning the laser delay. If the laser precedes the X-ray it has no influence on the spectra, because Ne cannot be energetically accessed. If the laser arrives too long after the X-ray it also has no influence because all the Ne+ produced by the Auger cascade have already decayed further. But if the laser delay is comparable with the Ne+ lifetimes, in the ns regime, the laser pulse can alter the population distribution of the various Ne+ states, which is naturally mapped into a change of the 2nd-step Auger spectra. We monitor the Auger electron spectra and control the relative delay between the X-ray and laser pulses as well as laser wavelength and intensity. From these delay-resolved Auger spectra we can extract dynamic information concerning the Ne+ involved in the cascade. Lifetimes are extracted and compared with theoretical calculations.

Speaker: Dr De Fanis Alberto (European XFEL)

16:00 Fluorescence measurements from x-ray irradiated liquid water

The investigation of the decay dynamics of liquids and solutions after x-ray irradiation became accessible in recent years owing to the tremendous progress in liquid microjet techniques. This method meets the high vacuum conditions required for experiments using x-ray excitation at synchrotron radiation facilities. Mainly via electron spectroscopy, several non-local de-excitation processes and intermolecular interaction mechanisms were identified. Their role in radiation biology is currently lively discussed. However, the detection of charged particles as a probe for decay mechanisms is constrained due to their short escape length in dense media. We present a complementary experimental method in which fluorescence detection is used to investigate reaction products after excitation of liquid microjets with synchrotron radiation. This approach is especially beneficial to track neutral and long-living species.

Speaker: Mr Christian Ozga (Institute for Physics and CINSaT, University of Kassel, 34132 Kassel, Germany)

16:30 Results and gaols from FS-SCS from Spectroscopy on gases and liquids

Oral

Speaker: Dr Leif Glaser (FS-SCS)

17:00 → 17:30 Coffee break

Coffee break

17:30 → 19:00 User reports

User reports

17:30 Photon-Ion Merged-Beams Experiments at PIPE: Recent Achievements and Outlook

oral

Speaker: Prof. Stefan Schippers (Justus-Liebig-Universität Gießen, I. Physikalisches Institut)

18:00 Absorption Spectroscopy of small molecular ions

The photoabsorption behavior of IH(n+) (n=2..5) molecular ions around the iodine 3d absorption edge will be presented as well as the calibration of the partial cross sections on absolute scale. As a second topic the present status of Traptor will be discussed.

Speaker: Dr Stephan Klumpp (DESY)

18:30 Multicoincidence studies at PO4 using COLTRIMS

abstract needed?

Speaker: Till Jahnke (IKF, Uni FFM)

19:00 → 20:00 Poster session

Poster session

19:00 Poster session

poster

Speaker: Various

20:00 → 22:00 Dinner

Dinner

Wednesday 24 February

09:00 → 10:30 User reports

User reports

09:00 X-ray holographic imaging of magnetic nanostructures and spatial coherence determination

We present X-ray holographic microscopy (XHM) and X-ray resonant magnetic scattering (XRMS) experiments to explore, on the one hand, the thickness-driven evolution of magnetic domain patterns in wedge-shaped Co/Pt and Co/Pd multilayer samples and on the other hand the magnetic state of magnetic multilayer nanodots with a diameter of 60 nm in varying out-of-plane magnetic fields. Additionally we demonstrate a new method to extract the two-dimensional spatial coherence function using magnetic speckle pattern.

Speaker: Mr Kai Bagschik (Institute of Nanostructure and Solid State Physics)

09:30 Time-resolved X-ray imaging of a magnetic bubble’s gyrotropic motion

Skyrmions are winding vector fields with a characteristic spherical topology. One example for such a vector field is the winding spin structure of a magnetic bubble in thin-film material with out-of-plane magnetization. Recent theoretical investigations predict a GHz gyrotropic motion of such a topological configuration after excitation in a restoring potential, analogous to vortex gyration. However, in contrast to vortices, bubbles are predicted to exhibit inertial effects, manifesting themselves in a second gyrotropic mode of reverse chirality and in additional degrees of freedom. Here, we present time-resolved images of the gyration of a magnetic bubble recorded using soft-X-ray Fourier-transform holography (FTH). The motion is triggered by a magnetic field pulse and the pump-probe image sequence is acquired with 50 ps time resolution using the single-bunch mode of the BESSY II storage ring. The microcoil to administer the magnetic field pulses has been lithographically integrated into the mask defining the FTH geometry. From the images, we extracted the relaxation trajectory of the bubble with a position precision of 3 nm. We find that two eigenfrequencies are required to describe the bubble’s motion leading to the conclusion that the bubble possesses a quasi-particle inertial mass. We attribute the comparatively large mass to the non-local energy reservoir of the bubble’s breathing mode.

Speaker: Dr Bastian Pfau (Max-Born-Institut)

10:00 Water Window Ptychography

Imaging of biological samples in the water window energy range offers high chemical contrast between organic soft tissue and water. Lens based microscopes are limited by their optical elements. The coherent X-ray diffractive imaging (CXDI) method extends resolution down to the nano scale. In order to measure samples of micrometer sizes at 25 nm resolution we used ptychographic coherent diffractive imaging (PCDI). Images of a test pattern and a fibroblast cell have been reconstructed from their diffraction patterns.

Speaker: Mr Max Rose (PIER Fellow / DESY)

10:30 → 11:00 Coffee break

Coffee break

11:00 → 13:00 User reports

User reports

11:00 ASPHERE III at P04: Momentum, spin, and position resolved photoelectron spectroscopy

ASPHERE III is a BMBF funded angle-, spin-, and position-resolving photoelectron spectrometer that fully exploits the unique capabilities of the variable polarization soft X-ray beamline of PETRA III. Combining a highly efficient Scienta R4000 photoelectron analyzer with the brillant, widely tunable, and highly monochromatic photon beam of the beamline and, complementary, with the monochromatized beam of a VUV-He- and Xe-plasma source, the experimental setup enables the direct comparison between bulk and surface electronic structures of solids. Since the analyzer can be rotated around the sample by a UHV goniometer, complete three-dimensional band structures and Fermi surfaces can be determined without sample rotation at a spatial resolution given by the synchrotron spot size. Moreover, the measured momentum- and position-resolved electronic structure can directly be connected with the geometric structure determined by XPD from the same spot on the sample and by STM and LEED from the same sample surface. In addition, the installed 3D-Mott spin detector enables the investigation of the momentum-dependent magnetic properties that can be compared to complementary atomic-site specific XMCD and XLD measurements. All spectroscopic investigations can be performed in situ
 and in real time during sample temperature changes controlled with a He-flow cryostat as well as during deposition of alkali and transition metals on sample surfaces. In this talk the current status as well as the further developments that are planned for ASPHERE III will be elucidated.

Speaker: Dr Matthias Kallaene (University of Kiel)

11:30 Signatures of the Strong Topological Character of the Bulk ZrTe5

ZrTe5 has recently stimulated in-depth investigations aimed at clarifying its ground state electronic properties. In fact, the material has been proposed to be a 3D Dirac semimetal [1], a prototype of weak topological insulator [2] or a topological insulator in proximity of a topological phase transition [3]. Here we report a comprehensive experimental and theoretical study of both its electronic and structural properties, revealing that the bulk stoichiometric ZrTe5 is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we resolve at the top of the valence band both a surface and a bulk state. The band dispersions are well captured by ab-initio fully relativistic calculations for the STI case, for the specific interlayer distance value measured in our x-ray diffraction study. Finally, scanning tunneling spectroscopy shows that the sample surface is metallic, with no band gap in the density of states, thus confirming the strong topological character of ZrTe5. [1] Qiang Li et al., Nature Physics (2016), doi:10.1038/nphys3648. [2] R. Wu et al., arXiv:1601.07056 (2015) [3] H. Weng et al., Physical review X 4, 011002 (2014).

Speaker: Ms Giulia Manzoni (University of Trieste, Trieste, Italy)

12:00 Probing the electronic structure of magnetic topological insulator (BiSbV)2Te3 thin films with soft X-ray photoelectron spectroscopy

We investigated the electronic structure of (BiSbV)2Te3 thin films by means of X-ray photoemission (XPS) and absorption (XAS) spectroscopy. This system is a three-dimensional magnetic topological insulator, recently reported as an anomalous quantum Hall system. The films were epitaxially grown on a Si(111) crystal and covered by a Se cap to avoid contamination during exposition to air. After thermally desorbing the Se cap, the core-level lines of the constituent elements and the V L2,3 absorption edges were measured for different V concentrations (0, 2 and 4 at.%). Our data evidence the incorporation of Se atoms in the film. By means of resonant photoemission we identify the signature of the V 3d states at the Fermi level, which may contribute to the exotic transport properties of the system. We show that our techniques are well suited for the study of the electronic properties of this novel class of materials.

Speaker: Dr Thiago Peixoto (Universität Würzburg, Fakultät f. Physik u- Astronomie, Lstl. f. Experimentelle Physik VII)

12:30 Rapid Fermi-Surface and Fermi-Velocity Mapping Using ToF Momentum Microscopy

The shape of the Fermi surface and the Fermi velocity vF as a function of direction in k-space are of high importance for the design of materials with tailored electronic properties. Moreover, the topology of the Fermi surface plays a crucial role in the existence of topologically non-trivial electronic states like the metallic states in the surface region of topological insulators. The novel experimental technique termed time-of-flight momentum microscopy has been applied for the first time in the soft X-ray range at P04. We determined the topology of the Fermi surface, the character of p- or n-type conductivity and quantified vF on the full Fermi surface for the model case of W.

Speaker: Prof. Gerd Schoenhense (University of Mainz, Inst fuer Physik)

13:00 → 14:00 Lunch break

Lunch break

14:00 → 15:30 User reports

User reports

14:00 Scanning Transmission and Fluorescence X-Ray Microscope for P04 – First Results

We present a scanning X-Ray Microscope, which uses a zone plate to focus the beam to a roughly 100 nm spot size onto the sample. Images are taken by scanning the sample through the focus and detecting the transmission signal with an area detector (CCD) and the fluorescence signal with a SDD detector. X-Ray microscopy, especially in the tender energy region of several hundreds of eV to some thousands of eV provides a powerful tool for the analysis of biological and biomedicine samples. Hence, it is widely used to gain more insight in health issues like transport mechanisms of lipids or toxicity and clearance properties of nanoparticles. The advantages of a scanning mode in comparison to the common full-field mode are the different possible imaging options in combination with an array detector (CCD) for transmission and the possibility of detecting the fluorescence radiation laterally resolved. The imaging options for scanning mode in transmission are not only the overall absorption, but phase contrast and dark-field images can be extracted from the data of the area detector as well. The image-contrast of a phase contrast image is much higher compared to a simple absorption image, so that not only the difference between high (bone) and low (tissue) absorption can be distinguished, but also structures in tissue itself can be revealed. The advantage of the fluorescence mode is the access of the elemental distribution. For some biomedical application it is not only of interest where certain particles settle, but also how the elemental distribution within the particles look like. Or the distribution of elements within certain big cells become of more and more interest in the biomedicine. Within our project we implemented the scanning option together with a fluorescence detector in a full-field microscope and we will present first results done at the P04 beamline of PETRA III. In our first experiments we were able to resolve 200 nm structures from a sine star in transmission and fluorescence mode. First experiments on biological samples were performed afterwards. The present status of the project will be presented.

Speaker: Dr Lars Lühl (Technische Universität Berlin)

14:30 Fluorescence Measurements and Perspectives with Superconducting Tunneling Junctions (STJ)

The use of STJ’s as absorber material for spectroscopic Soft X-Ray detection is very promising in terms of energy resolution and count rate capabilities. Because of the low excitation energy of Cooper pairs in a superconductor (few meV) three orders of magnitude more charge carriers than in a Si-detector are produced per photon. The ultimate resolution limit for such a detector is therefore in the order of a few eV instead of a few 100 eV in the soft X-ray regime. The first commercially available 36 pixel STJ detector is characterized and implemented into synchrotron radiation beamline operation. The achieved resolution is 10eV for 500 eV photons and 50eV for 1500eV photons with a maximal count rate of 10 kcps per pixel. This allowed for element specific Soft X-Ray fluorescence measurements at the P04 beamline at Petra III, DESY.

Speaker: Mr Ivan Baev (Physics Department, University of Hamburg)

15:00 Status of the Percival Soft X-ray Imager Development

oral

Speaker: Dr Jonathan Correa (DESY, FS-DS)

15:30 → 16:00 Open discussion and meeting summary

Open discussion and meeting summary