Fundamentals and Dynamics of Energy Transport and Conversion

1. h CB Dye VB (TiO2)n Interfacial electron transfer in Dye-sensitized solar cell XAS (absorption) XES (emission) XRS (scattering) Fundamentals and Dynamics of Energy Transport and Conversion Sensitive to all species in the solvent Element specific, sensitive to local structure EXAFS yields change in bond length Yields excited state geometric structure Natural photosynthesis X-ray emission spectroscopy Spin R Kα X-ray absorption spectroscopy X-ray diffuse scattering TiO2 Catalyst Aqueous [Fe(bpy)3]2+ Q XANES: sensitive to electronic and geometric structure (oxidation state, valence orbital occupancy, charge transfer) SrO H. Wen, G. Doumy, B. Adams, A. D. DiChiara, E. M. Dufresne, T. Graber, Y. Li, A. M. March, Q. Kong, A. R. Sandy, S. H. Southworth, D. A. Walko, J. Wang, X. Zhang, Y. Zhu Time-Resolved Research, Atomic Molecular and Optical Physics, and Structural Science Groups, X-ray Science Division, Advanced Photon Source, Argonne National Laboratory Introduction Kα, Kβ sensitive to electronic structure, not geometric structure 153 ns Bio-inspiration Determine structures of transient intermediates Insight into solvent shell rearrangements TiO2 J. Phys. Chem. Lett.  2, 628 (2011). Angew. Chem. Int. Ed.  51, 12711 (2012). e- The time-resolved research program at the Advanced Photon Source is targeted at understanding the fundamentals of energy transport and conversion at multi- energy, length and time scales utilizing a suite of advanced ultrafast hard x-ray probes localized at Sector 7, 11 and 14. Orbital Charge … TiO2 Relay Science  337, 1200 (2012). High spin (spin and oxidation state, electronic correlations) Kβ TiO2 EXAFS: local bond distances and coordination numbers 5um SrO Low spin Time Bandwidth DUETTO TiO2 t ~650 ps e- Lattice -electronic and geometric structure Photosensitizer … -insight into solvent shell rearrangements PbO Relay (R) Opportunities for time-resolved x-ray science at the Advanced Photon Source -direct probe of spin state TiO2 X-ray probe hn Input for XAS analysis CB Input for scattering analysis PbO + 50 kHz - 6.52 MHz 10 ps and 130 ps Dye Photosensitizer (PS) Catalyst (C) TiO2 VB - Photosystem 1 (TiO2)n Spatiotemporally resolved hard x-ray probe Diverse pump sources: Optical, electrical, mechanical and THz excitations Excited state fraction High repetition rate lasers to fully exploit high flux of the APS Phys. Chem. Lett.  4, 1972 (2013). Light Conversion PHAROS New! Optical excitation Tunable (0.2-16 mm) Up to 1 MHz 250 fs Electric field pulse Natural photosynthesis Artificial photosynthesis solar fuels: Light → chemical energy 266 nm 2.5 W (4 μJ/pulse) @ 600 kHz Laser shock excitation Artificial photosynthesis solar cells: Light → electricity THz radiation@Sec7 Molecular machines Resolution: ~260 nm, ~80 ps Ultrafast Materials Science: Understanding and controlling energy transport and conversion among multiple degrees of freedom Valence-to-Core sensitive to chemically relevant orbitals Ultrafast Chemical Science: Elucidating the mechanisms of light induced chemical processes Dye Sensitized Solar Cells Motivation: harnessing the power of light Combined Techniques for Complimentary Information Motivation:Controlling the interplay of electronic, magnetic, optical, mechanical, and thermal properties of materials for efficient energy transport and conversion. Scintillator Liquid jet Laser APS Standard Operating Mode KB Mirrors APD - - - - - - - - - - - - - - - - Energy Conversion + + + + + + + + - - - - X-rays Pilatus + + + + + + + + + + + + + + + + + + + + - - - - Visualizing trans-cisisomerization pathways 3 ft. x 3 ft. table Superionic phase transition Electronic origin of photoinduced strain in multiferroics Ion chamber 35 nm BiFeO3 on SrTiO3 (001) 1 m Rowland circle • Provides a large flux in well separated pulses 400 nm All those techniques can now be applied to study transient states ! θo Analyzer crystal 0.4% strain 80 ps FWHM Showcase experiments using X-ray absorption Electron transfer inside a biomimetic supramolecular complex for solar fuel catalysts X-rays 6.52 MHz Delay (ns) X-ray pulse spacing is large enough to isolate signal from individual x-ray pulses ~106 photons/pulse at 7ID-D ~1010 photons/pulse at 14ID-B Sector 11ID-D A versatile Time resolved X-Ray Absorption setup Complex chemical reactions can be initiated by light and recorded on physically relevant time scales, paving the way for the exploration of of life’s most sophisticated processes. t<0 t=0 t>0 Electron transport inside iron oxide nanoparticles Using ultrafast optical and x-ray probes, we found optically excited carriers screen the depolarization field, which gives rise to significant localized strain as a result of inverse piezoelectric effect. Wen, et al., Phys. Rev. Lett.110, 037601 (2013) Schick, et al., Phys. Rev. Lett. 112, 097602 (2014) T. A. Miller et al., Nature Comm. 4, 1369 (2013) Y. O. Jung et al., Nature Chem. 5, 212(2013) Energy Transport Capturing excited state structures at high precision by using full APS flux First demonstration of combined techniques in a pump-probe experiment Electric-field-driven domain dynamics Time- and momentum-resolved heat transport Energy transport in nanostructured materials Optical intensity I(x,t) BiFeO3 X-ray emission energy Sector 7ID-D Combined techniques setup Intensity (a.u) c Incident x-ray energy K. Haldrup et al., J.Phys Chem. A 116, 9878 (2012) G. Vanko et al, JESRP 188, 166 (2013) - Position (µm) FeRh a Lattice structure (x,t) Using flux demanding techniques for time resolved studies: efficient detection at high rep-rate Kaground state Ka100 ps delay Intensity (a.u) The time-resolved changes of the diffuse scattering show primarily a quasi-thermal phonon distribution that is established in 100 ps and that follows the time-scale of thermal transport. Ex: Von Hamos crystal analyzer for TR-XES ZnO nanoparticles: Observe evolution of charge distribution Laser excitation and x-ray detection @ 1.3 MHz ZnO (35 nm particles) in water @355 nm Optical pulse promotes electrons in conduction band Only ~1% excited state fraction Time-resolved RIXS difference map Data consistent with increased electron density on Zn centers Also demonstrated simultaneous measurement of Ka, Kb and Valence to Core XES Kb ground state Kb 100 ps delay Position (µm) The spatiotemporal-resolved structural probe reveals the deviation of the relaxation process from a sinusoidal profile that quantitatively measure the in-plane transport processes. J. Chen, et al., Appl. Phys. Lett. 102, 181903 (2013). P. Chen, et al., Phys. Rev. Lett.110, 047601 (2013) J. Szlachetko et al., RSI 83, 103105 (2012). The Advanced Photon Source is funded by the U.S. Department of Energy Office of Science Advanced Photon Source • 9700 S. Cass Ave. • Argonne, IL 60439 USA • www.aps.anl.gov • www.anl.gov