Femtosecond Soft X-Ray Probing of Electron Dynamics at Photocatalytic Material Surfaces
Technical Report,01 Aug 2014,31 Jul 2019
REGENTS OF THE UNIVERSITY OF CALIFORNIA BERKELEY United States
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A strategy that has found much success for semiconductor photocatalysis involves the creation of junctions of semiconductors with metals, either as thin films or as particles. Such materials are often observed to possess significantly higher activities and corrosion resistances when compared to a semiconductor alone. Understanding the effect of metal deposition on photocatalysts requires an understanding of the electronic structure of the junction as well as the behavior of the electrons and holes generated by solar radiation. In this report, A new apparatus has been constructed that produces extreme ultraviolet ultrafast laser pulses, which can be used for time resolved photoemission. Static spectra reveal the growth modes of metals on semiconductors and time-resolved studies show photovoltage shifts that reveal the dynamics of electron or hole carriers moving from one layer into another. In several studies, zinc junctions on silicon Si100, both films and nanoparticles, and a Znn-GaP100 junction were studied using the ultrafast time-resolved extreme ultraviolet XUV photoemissiontechnique. The approach to metal character was revealed versus the size of the particles. Schottky barrier principles were elucidated, including new results demonstrating that core level transitions can reveal the changes in electron temperature in the same way as changes in Fermi electron distributions do. Using XUV transient absorption to look through a junction, layer-specific time-resolved results are obtained for the hole transport across a Si-TiO2-Ni photoanode junction. The results indicate that the XUV photoemission and transient absorption techniques are highly suitable for studying the carrier dynamics of a wide range of junctions.
- Nuclear Physics and Elementary Particle Physics
- Solid State Physics
- Electricity and Magnetism