title: Capturing interfacial photoelectrochemical dynamics with picosecond time-resolved X-ray photoelectron spectroscopy.
abstract: Time-resolved core-level spectroscopy using laser pulses to initiate and short X-ray pulses to trace photoinduced processes has the unique potential to provide electronic state- and atomic site-specific insight into fundamental electron dynamics in complex systems. Time-domain studies using transient X-ray absorption and emission techniques have proven extremely valuable to investigate electronic and structural dynamics in isolated and solvated molecules. Here, we describe the implementation of a picosecond time-resolved X-ray photoelectron spectroscopy (TRXPS) technique at the Advanced Light Source (ALS) and its application to monitor photoinduced electron dynamics at the technologically pertinent interface formed by N3 dye molecules anchored to nanoporous ZnO. Indications for a dynamical chemical shift of the Ru3d photoemission line originating from the N3 metal centre are observed ∼30 ps after resonant HOMO-LUMO excitation with a visible laser pump pulse. The transient changes in the TRXPS spectra are accompanied by a characteristic surface photovoltage (SPV) response of the ZnO substrate on a pico- to nanosecond time scale. The interplay between the two phenomena is discussed in the context of possible electronic relaxation and recombination pathways that lead to the neutralisation of the transiently oxidised dye after ultrafast electron injection. A detailed account of the experimental technique is given including an analysis of the chemical modification of the nano-structured ZnO substrate during extended periods of solution-based dye sensitisation and its relevance for studies using surface-sensitive spectroscopy techniques.
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA. sneppl@lbl.gov ogessner@lbl.gov.
authors.forename: Stefan
authors.initials: S
authors.lastname: Neppl
authors.forename: Andrey
authors.initials: A
authors.lastname: Shavorskiy
authors.forename: Ioannis
authors.initials: I
authors.lastname: Zegkinoglou
authors.forename: Matthew
authors.initials: M
authors.lastname: Fraund
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Slaughter
authors.forename: Tyler
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authors.lastname: Troy
authors.forename: Michael P
authors.initials: MP
authors.lastname: Ziemkiewicz
authors.forename: Musahid
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authors.lastname: Ahmed
authors.forename: Sheraz
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authors.lastname: Gul
authors.forename: Bruce
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authors.lastname: Rude
authors.forename: Jin Z
authors.initials: JZ
authors.lastname: Zhang
authors.forename: Anton S
authors.initials: AS
authors.lastname: Tremsin
authors.forename: Per-Anders
authors.initials: PA
authors.lastname: Glans
authors.forename: Yi-Sheng
authors.initials: YS
authors.lastname: Liu
authors.forename: Cheng Hao
authors.initials: CH
authors.lastname: Wu
authors.forename: Jinghua
authors.initials: J
authors.lastname: Guo
authors.forename: Miquel
authors.initials: M
authors.lastname: Salmeron
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bluhm
authors.forename: Oliver
authors.initials: O
authors.lastname: Gessner