IRSEC'15 - Emad Flear Aziz - Probing the Ultrafast Processes in Photo-Catalytic Materials

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