Probing the Ultrafast Processes in Photo-Catalytic Materials

Prof. Emad Flear Aziz
Institute director of Methods for Material Development at Helmholtz-Zentrum Berlin, Germany
Professor at the department of Physics at FU-Berlin, Germany
Guest professor at Institute for Molecular Science, Okazaki Japan &
Head of the Joint Ultrafast Dynamics Lab in Solutions and at Interfaces [JULiq]

Prof. Emad Flear Aziz, Institute director of Methods for Material Development at Helmholtz-Zentrum Berlin, Germany

The study of the electronic and structural dynamics in solids, solutions, and at the interfaces between them has received much attention during the past years. The interest and the importance of these studies arise from the fact that the ultrafast electron dynamics is the key player in novel photo-catalytic materials and their function. Different time-resolved spectroscopic methods, including transient absorption and fluorescence as well as transient electron photoemission spectroscopy (PES), are developed to explore the electron dynamics induced in such materials. In my talk I will focus on the time-resolved electron detection, for the case of initiating the electron dynamics by a UV/visible laser pulse, and interrogating the evolving relaxation using an ultrashort XUV high-order harmonic generation (HHG) light pulse. At a XUV photon energy the entire valence photoelectron spectrum can be measured in a one-photon ionization process. We employ a HHG setup which we recently developed for time-resolved spectroscopic studies on solutions [1]. Using this novel femtosecond light source I will present two topics. I first report on the ultrafast dynamics of electron transfer at the interface between a ruthenium-dye complex and TiO2 nanoparticles [2]. The second topic then discusses the analogous processes in an aqueous environment, using a vacuum liquid microjet [3]. A short overview of photoelectron spectroscopy applied to liquid micro-jets, using soft X-rays from a synchrotron-light facility and from the XUV HHG source [4] will be presented.
References:
[1] J. Metje, M. Borgwardt, A. Moguilevski, A. Kothe, N. Engel, M. Wilke, R. Al-Obaidi, D. Tolksdorf, A. Firsov, M. Brzhezinskaya, A. Erko, I. Y. Kiyan, E. F. Aziz. Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates. Op. Ex. 22, pp 10747-10760 (2014)

[2] M. Borgwardt, M. Wilke, T. Kampen, S. Mähl, W. Xiang, L. Spiccia, K. M. Lange, I. Y. Kiyan, E. F. Aziz. Injection Kinetics and Electronic Structure at the N719/TiO2 Interface Studied by Means of Ultrafast XUV Photoemission Spectroscopy. J. Phys. Chem. C 119 (17), pp 9099–9107 (2015)

[3] R. Al-Obaidi, M. Borgwardt, M. Wilke, J. Metje, A. Moguilevski, N. Engel, D. Tolksdorf, A. Raheem, I. Yu. Kiyan,∗ and E. F. Aziz. Ultrafast photoelectron spectroscopy of solutions: Space-charge effect. New J. Phys. Accepted (2015)

[4] Emad F. Aziz, Niklas Ottosson, Manfred Faubel, Ingolf V. Hertel, and Bernd Winter. Interaction Between Liquid Water and Hydroxide Revealed by Core-Hole De-Excitation. Nature 455, 89 (2008)

Biography

Prof. Dr. Emad Flear Aziz finished his doctor at the chemistry department of Freie universität Berlin in 2007. He made his postdoctoral researcher at the École polytechnique fédérale de Lausanne (2008) followed by another postdoctoral researcher at BESSY Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung GmbH (2008/2009). He succeded to attract starting grant as Helmholtz young investigator group (2009) and European research council, ERC-Starting grant (2011) where he build two teams at Helmholtz-Berlin and Freie Universität Berlin. He also got to be guest professor at the Institute of Molecular Science, Okazaki, Japan (2014). Currently, he is the director of the institute “Methods for Material Development” at Helmholtz-Zentrum Berlin für Materialien und Energie (since 2014) and Full professor (W3) “Structure and Dynamics of Functional Materials in Solution” at Freie Universität Berlin (since 2015).

He is developing spectroscopic methods to study novel materials in solution and at interfaces varying from ions and simple biochemical complexes up to complex systems like solar cells, catalysis and proteins in solution and at interfaces. He is using and developing methods based on large scale wavelength, from far infra-red up to soft X-ray, offered by synchrotron and laser based source. Examples of such methods are soft X-ray absorption (XAS), emission (XES) and photoelectron spectroscopy (XPS), resonant inelastic X-ray scattering (RIXS), infrared spectroscopies (IR) and microscopies. He is combining as well fs/ps laser pump/probe scheme to follow ultrafast electronic and structure change of molecules under real conditions. With the European Research grant (ERC), he construct a femto-lab based on pump-probe technique using the 20 fs laser pulse as a pump and the high harmonic generated (HHG) extreme ultraviolet (EUV) as a probe for system under ambient conditions (micro-jet and liquid-solid interfaces). The probe method is ultra-violet, extreme ultra-violet and X-ray photo-electron spectroscopy, X-ray absorption and emission spectroscopy. The goal of the joint Freie Universität Berlin and Helmholtz Zentrum Berlin lab is to follow dynamics in femtosecond time scale and probe structure in sub-nanometer scale for biochemical materials in solution and at interfaces.

His research activities have been recognized with several awards and prizes with the recent Nernst-Haber-Bodenstein-Preis from the physical chemistry society.