Alle Plätze belegt - keine Anmeldung mehr möglich!

Experimentierpraktikum in den Sommerferien für Schülerinnen und Schüler. Sonnensegel eines Satelliten klappen auf, ganz ohne Motor. Eine High-Tech-Zahnspange hält die Zähne in richtiger Position und Brillengestelle werden unverwüstlich. Dieses und vieles mehr erlauben Materialien, die über ein „Formgedächtnis“ verfügen. Du wirst  im Rahmen dieses halbtägigen Kurses dem Geheimnis der Drähte durch eigenes Experimentieren auf die Spur kommen. (Angebot für 10 bis 14-jährige)

Eintägiges Experimentierpraktikum in den Sommerferien für Schülerinnen und Schüler.
Kennst du Hologramme? Weißt du wie sie entstehen? Im Schülerlabor des Helmholtz-Zentrums Berlin lernst du nicht nur Hologramme kennen und verstehen, sondern kannst sogar dein eigenes Hologramm erstellen! (ab 15 Jahre)

There has been dramatic progress in recent years both in ab initio calculations and in the interpretation of various x-ray spectroscopies, e.g., x-ray absorption spectra (XAS) and inelastic x-ray scattering (IXS). Together with advances in analysis methods, these developments now permit an interpretation of experimental data in terms of structural and electronic properties of a material. We first summarize these advances, focusing on a heuristic explanation of the real-space Green's function (RSGF) approach used in the FEFF code [1]. The RSGF approach builds in some key many-body corrections to the independent particle approximation, and thus differs from conventional electronic structure and quantum chemistry calculations based on wave-functions and density functional theory. The method is illustrated with applications to complex materials ranging from catalysts and minerals to bio-structures and aqueous systems. Finally we discuss some recent theoretical developments leading to a new generation of codes including FEFF9 [2] and the Bethe-Salpeter Equation code OCEAN [3].

^{[1] J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).
[2] J. J. Rehr, J. J. Kas, M. P. Prange, A. P. Sorini, Y. Takimoto, F. Vila, Comptes Rendus Physique, 10, 548 (2009).
[3] J. Vinson, E. L. Shirley, J. J. Rehr and J. J. Kas, UW Preprint (2010).
*Supported by DOE Grant DE-FG03-97ER45623 and facilitated by the DOE CMSN.}

Das HZB lädt  am 5.6.2010 von 17 bis 1 Uhr nachts zur Langen Nacht der Wissenschaften an den Standorten Adlershof und Wannsee ein. Details aus dem Programm finden Sie unter: https://www.helmholtz-berlin.de/aktuell/events/langenacht/index_de.html

Observing Function with X-rays

Zielgruppe sind Studienräte mit naturwissenschaftlichen Fächern. Im Rahmen dieser Lehrerfortbildung möchten wir Ihnen Neutronenquellen sowie verschiedene Methoden der Materialanalyse mit Neutronen vorstellen.

Zielgruppe sind Grundschulpädagogen.  Es werden nicht nur die Versuche des Schülerlabors, sondern vor allem auch Experimente vorgestellt, die Sie in Ihren Unterricht übernehmen können.

Der Kompetenzverbund  NanoSOFT innerhalb der Verbundforschung des BMBF zur Erforschung kondensierter Materie an Großgeräten veranstaltet in Zusammenarbeit mit dem Helmholtz-Zentrum Berlin für Materialien und Energie einen 2-tägigen Workshop zur Unterrichtung der wissenschaftlichen Öffentlichkeit über die in NanoSOFT betriebenen Instrumentierungsprojekte.

With the political agreement in early summer 2009 to choose a site for the ESS, a significant number of European countries (14 at the time of writing) has joined together in a partnership to embark on a 3-year Design Update prior to starting construction on the site in Lund in southern Scandinavia. The ESS will be a 5MW long pulse spallation neutron source for the study of materials in all their diversity. As such it will a unique and uniquely powerful facility offering new opportunities for research. Compared to the user’s experience today the ESS will offer measuring capabilities two orders of magnitude enhanced. One of the features of the ESS project is the goal to be fully sustainable in terms of energy consumption. Using technology which is already tried and tested in Sweden, the ESS will be a carbon neutral facility creating its electrical power by renewable means and recycling cooling water into the Lund district heating system. Not only is this environmentally responsible but it will reduce operating costs and guard against the effects of fluctuations in the energy market.

Soft Matter Science@HZB: Present Status and future Perspectives

AGENDA
14:00–14:15 Welcome
14:20–15:00 Addresses by the Representatives
from FU, HU, MDC, FMP
15:05–15:30 Official Opening
15:45–16:45 Lecture by Nobel Prize Laureate 2009 Prof. Dr. Ada Yonath
17:00 Reception

Liebe ehemaligen Mitarbeiter! Die Zeiten für den Shuttleservice zum Neujahrsempfang am 28. Januar stehen nun fest.

Hinfahrt: Wannsee - Adlershof
Abfahrtszeit: 13:00 Uhr
Abfahrtsort: vor der Pforte

 Bitte seien Sie mindestens 10 Minuten vor Abfahrt vor Ort.

Rückfahrt: Adlershof - Wannsee
Abfahrtszeit: ca. 16:15 Uhr
Abfahrtsort: Bunsenstrasse (Ausgang Terrassenseite - Rückseite WISTA-Gebäude)

Die Busse werden pünktlich abfahren.

 Für Fragen stehe ich Ihnen jederzeit zur Verfügung.

Mit freundliche Grüßen Britta Heidrich
Abteilung Kommunikation
britta.heidrich@helmholtz-berlin.de
Tel: 030/ 8062 2735

The workshop consists of invited  talks and panel discussions on present status and future prospects of chalcopyrite solar cells. The number of  participants will be limited to about 100, including the most internationally renowned experts.

The workshop is organized by PVcomB (Competence Centre Thin-Film-  and Nano-technology for Photovoltaics Berlin)

Die diesjährige SEI-Frühjahrstagung (100. Tagung!) findet vom 15. bis 17. März 2010 am DESY in Hamburg statt. Verantwortlicher ist letztmalig Herr Dr. Friedrich Wulf.

Aktuelle Informationen finden Sie unter https://www.helmholtz-berlin.de/events/sei/index_de.html

BEGINN: 13.10.2009 Vorlesung und Übung (20 135) - 3-stündig, ECTS: 5 Begleittermin: Donnerstag ab 16:00 Uhr, Albert-Einstein-Str. 15, Berlin Adlershof (BESSY II) ODER Wannsee, Glienicker Str. 100 Modern sources of synchrotron radiation (SR) and neutrons are very powerful tools in a wide range of important research activities, ranging from biology and medicine to solid state physics and micro/nano-technology. This Lecture Series will provide a basic knowledge of the operational principles, control and manipulation of SR and neutron beams as well as describing their main characteristics. X-ray and neutron optics will be described in detail, as well basic experimental techniques such as absorption, photoelectron spectroscopy, diffraction analysis and wide/small angle scattering for both types of beams. Future perspectives for new source developments, i.e., X-ray Free Electron Lasers (FEL), Energy-Recovery X-ray Sources and new Neutron Sources will be included into the programme. Practical sessions are planned to take place at the at BESSY II storage ring in Adlershof and the neutron source at Wannsee to provide the students access to state-of-the-art instrumentation and methods.

Dephasing of surface plasmons

Plasmonics for improved photovoltaic devices mainly n-intrinsic-p a-Si:H solar cells

Fraunhofer-Institut für Solare Energiesysteme ISE, Freiburg

International Summer University on Energy 2010
Renewable Energies II: Photovoltaics & Solar Thermal

22^nd August to 3^rd September 2010 in Falera, Switzerland

The International Summer University on Energy (ISU^energy 2010) invites you to participate in two unforgettable weeks to learn, experience and enjoy a series of seminars on renewable energy in the Swiss Alps. The school integrates different academic fields such as Physics, Material Science, Material Engineering, Sociology, Political Science and Economics and it follows the successful ISU^energy  2009.

The ISU^energy 2010 will provide students with a solid foundation in photovoltaics and solar thermal technologies. Well-known researchers and scientists from leading universities and institutes will give lectures covering a wide range of topics on the principles of solar energy conversion. Theoretical knowledge will be complemented with practical workshops with special emphasis on hands-on experience.

The school primarily addresses students at Master level or to Diploma students (also young PhD students are welcomed) who prove to have an outstanding performance.

Responsible: Margarita Russina (G-I1) and Stefan Wellert (-F-I2)

Organic light-emitting diodes (OLEDs) have attracted much attention in the past decades, offering an competitive alternative to existing display technologies and inorganic solid state lighting devices. In comparison to existing technologies, OLEDs exhibit superior properties with respect to device efficiency and performance, fabrication costs and adaptive device design. For all above mentioned device implementations well defined material properties (carrier mobility, emission color, film forming properties, etc.) and in particular a high shelf and operational stability of the light emitting semiconductor are inevitable to achieve the targeted lifetimes of devices beyond ten thousand of hours. One pivotal point for the successful development of light emitting organic semiconductors is a profound spectroscopy based fundamental understanding of the structure to property relations in this class of materials. As discussed in this seminar many of the achievements towards reliable structure to property relations were made possible by the elucidation of the significant role of very low concentrations of chemical defects and other impurities as well as their interplay with optically and electronically excited states. In particular we will show how the fundamental insights from steady state [1] and time resolved optical pump-probe spectroscopy [2] lead to the desired and improved material properties based on a rational design of different macromolecules such as light emitting conjugated [3,4] polymers, dedritic polymers and multi chromophore dendrons [5].

Ultrafast X-ray Spectroscopy of Solvated Systems

Structural dynamics in molecular systems investigate the interplay of valence charge distributions, spin states and nuclear degrees of freedom in chemical reactions. Femtosecond core-level spectroscopy is very well suited to study such dynamics via x-ray absorption near-edge structure (for information on changes in valence charge distribution / spin-state) and via the extended x-ray absorption fine structure (for information in nuclear arrangements) to unravel underlying molecular mechanisms. Specifically, we have employed femtosecond core-level spectroscopy to study (i) hydrogen bonding in water and (ii) metal-ligand interactions in solvated transition metal complexes:
Water is characterized by a complex hydrogen bond (HB) network which fluctuates on multiple time-scales equivalent to tens of THz down to GHz and below.  Despite the vast literature on the structure and dynamics of water there is still much unknown and our experiments are first attempts to exploit femtosecond core-level spectroscopy to gain further insight into the nature of HBs in water ....

One common attribute of several classes of correlated electron materials is that the onset of conducting state in these systems typically occurs in the regime of nano-scale phase separation of chemical, and/or electronic/magnetic origin. We have systematically investigated the electromagnetic response of a prototypical correlated electron material VO₂ in the regime of phase separation using scanning infrared nano-scopy at length scales down to 10 nano-meter. In combination with more conventional infrared ellipsometry these studies uncover spectroscopic signatures of the Mott transition including divergent effective mass and electronic pseudogap  /Science 318, 1750 (2007)/. We demonstrated memory resistance and memory capacitance properties of VO₂ films that appear to be linked to phase separation in this enigmatic oxide /Science 325, 1518 (2009)/.

Electrocatalytic energy conversion processes in fuel cells are expected to play a major role in the development of sustainable technologies to mitigate global warming and to lower our dependence on fossil fuels. I will demonstrate how electron and x-ray spectroscopy can be used to address fundamental questions regarding the reaction mechanism of the oxygen reduction reaction (ORR) on Pt and probe the electronic structure of Pt and adsorbed species of model system Pt catalysts. From time resolved x-ray photoelectron spectroscopy (XPS) we have determined the activation barrier for the O₂ dissociation process on Pt to be in the range around 0.25 eV. Using in-situ studies under real electrochemical conditions of single crystal surfaces using high resolution Pt L-edge spectroscopy we have identified oxide growth at certain potentials that could have some major influence on the rate of the ORR reaction. Recent dealloyed Pt-Cu catalysts have shown an enhanced activity in comparison to pure Pt by factor of 5 tested in a real fuel cell [1]. We demonstrate that this activity enhancement comes from compression strain of the Pt lattice that leads to modifications of the Pt electronic structure and subsequently weakens the surface bond of adsorbed oxygen species.

1. R. Srivats et al. Angew. Chem. Int. Ed. 46, 8988 (2007)

The class of retinylidene proteins comprises hundreds of photochemically reactive members. It is characterized by the prosthetic group – the chromophore - retinal (vitamine A) and a 7-helical transmembrane structure. There are two families within this class: the microbial type rhodopsins with the ion pumps bacteriorhodopsin and halorhodopin, with sensory rhodopsin and the ion channel channelrhodopsin on the one hand, and the visual rhodopsins of vertebrates and invertebrates on the other hand. Despite the different functions of all these proteins, they share some structural similarities.In the last years, many details of the light-induced photocycles and/ or cascades of these proteins have been revealed. Infrared spectroscopy has been a powerful tool to study these alterations since it allows to monitor conformational changes and proton transfer reactions on a molecular level.The talk will focus on infrared spectroscopy of two members of the two rhodopsin families, namely the microbial channelrhodopsin which - as a light gated cation channel - has recently experienced large applications in neurophysiology, and the visual pigment rhodopsin, which plays a decisive role in the light induced signal transduction cascade and is the prototype of a G-protein coupled receptor.

Water is the key compound for our existence on this planet and it is involved in many important physical, chemical, biological and geological processes. Although water is the most common molecular substance it is also most unusual with many anomalies in its thermodynamic properties such as compressibility, density variation and heat capacity. The question of the structure of the hydrogen bonding network in water has been discussed intensively for over 100 years and has not yet been resolved. This talk will describe recent x-ray spectroscopy and scattering measurements showing that the liquid can be described as fluctuations between two types of local hydrogen bonded structures driven by incommensurate requirements for minimizing enthalpy and maximizing entropy. The connection of these results to low and high density water and the 2^nd critical point model will be discussed. Ion solvation, hydrophobic interactions and bonding to metal surfaces will also be discussed.

The metal L2,3 x-ray absorption near-edge structure (XANES) of 3d transition metal (TM) compounds shows widely spread multiplet structures because of the strong interaction between the core TM-2p and 3d electrons. Therefore, one-electron calculations cannot reproduce the experimental spectra in general. The charge transfer multiplet method is the most prevalent and conventional theoretical approach for the analysis of TM-L2,3 XANES[1]. Although this approach has been successful in reproducing many experimental spectra, it cannot be used to predict multiplet structure a priori, because of the use of the adjustable parameters. An ab-initio calculation that takes multiplet effects into account is therefore strongly desirable.For this purpose, we have developed an ab-initio configuration interaction (CI) method for L2,3 XANES. In this method, fully relativistic molecular orbitals (MOs) obtained by relativistic density functional theory (DFT) are used to construct the many-electron wave-functions. The one-electron and the two-electron integrals, which determine the multiplet energies, are directly evaluated over MOs. All ligand field effects are included by using MOs. This technique has been successfully used to quantitatively predict TM-L2,3 spectra for a range of actual oxide geometries, without any adjustable parameters[2,3]. The charge transfer from ligand to TM can be included by adding more electronic configurations in the CI[4].

A variety of multiple ordering of spin, charge and orbital has been observed in 3d transition-metal compound. However, because of complexity of the system, it is difficult task to know the character of these ordered states as well as their formation mechanism.To elucidate the nature of these ordered states, resonant soft x-ray diffraction (RSXD) at the L2,3 edge has advantage, since it involves 2p core to 3d orbital excitation in its intermediate state and thus can provide direct and detail information on the 3d electronic state in addition to the ordering pattern. Since the transition matrix elements are intimately related to those of x-ray absorption spectroscopy at the L2,3 edge, RSXD shares many aspects of it; the Bragg peak intensity as a function of the photon energy (multiplet structures) strongly depends on the valences and configurations of the transition-metal ion sites which participate the corresponding ordering. The light polarization and azimuthal angle dependences of the intensity reflect the orbital symmetry and the direction of the spin moment in the initial state.

In this talk, it will be demonstrated with some examples (Mn and Ni perovskites, and magnetite (Fe3O4)) that how the information on 3d electronic state, and the character of the ordering can be extracted by the analysis using configuration-interaction cluster model. The interpretation of RSXD results on some of compounds, particularly on magnetite, is still controversial, because the lattice distortion caused by the ordering can contribute to the peak intensity as well. This issue will be also discussed.

By combining various ultrafast laser techniques with ps and fs X-ray absorption spectroscopy, we can fully indentify the photocycle of solvated systems. We will review some of our recent results on the solvation shell changes around atomic solutes, on binuclear molecular complexes, and on the structural changes induced by electron transfer and spin changes in metal-based molecular complexes.

The use of ultrashort terahertz pulses has facilitated terahertz spectroscopy of a wide range of physical, chemical and biological samples, and has enabled time-resolved measurements in which the terahertz pulse is used to probe dynamical responses to an optical excitation pulse. In almost all cases reported to date, the THz pulses have had rather low energy, field amplitude, and average power. This has slowed the development of nonlinear THz optics and spectroscopy as well as THz signal processing, spectroscopic imaging and screening, and other applications. Using an extremely effective terahertz radiation generation scheme pioneered by Hebling et al., we obtained one of the highest energy tabletop terahertz sources to date. By using strong THz radiation we have demonstrated nonlinear effects in semiconductors such as saturated absorption, intervalley scattering, self-phase modulation and impact ionization. These effects can be monitored time and frequency resolved using a novel THz-pump/THz probe scheme in the absence of band-to-band excitation. Our data show the effect of highly accelerated carriers and the strong coupling of the electronic system to the lattice on the picosecond timescale.

Abstract:
Angle-resolved photoemission (ARPES) has proven to be an invaluable tool to explore the
properties of novel materials like graphene. In this talk three aspects of graphene are
discussed. First, electron-phonon coupling in potassium doped graphene is studied, using the
unique access to many-body interactions that ARPES provides. The second topic is a surprising
dispersion of the C 1s core-level in graphene. Finally, it is shown that a bandgap can be
induced in graphene by chemical modification.
[1] M. Bianchi et al., Phys. Rev. B 81 (2010) 041403R [2] S. Lizzit et al., Nature Physics 6
(2010) 345 [3] R. Balog et al., Nature Materials 9 (2010) 315