Ultrafast XUV Probing of Electron Dynamics at Photocatalytic Surfaces and Junctions
Abstract
Previous research in this AFOSR program pioneered the investigation of vapor phase and aerosol ionic liquid photochemistry and dynamics, and a collaboration with Steven Chambreau and Ghanshyam (Gammy) Vaghjiani of AFRL produced many insights into the thermodynamic, kinetic, ultrafast, and photochemical properties of ionic liquids of interest for hypergolic and ion propulsion. The work on ionic liquids is essentially complete. In its place, a renewal program of experimental research on electron dynamics at the surfaces of photocatalytic materials was initiated, investigated by coupling photoelectron spectroscopy with ultrafast extreme ultraviolet (XUV) laser pulses produced by the method of high order harmonic generation (HHG). A new apparatus was constructed for this work, to probe the ultrafast dynamics of ultrahigh vacuum prepared, photoinitiated semiconductors and semiconductor surfaces decorated with particles and films of metals and metal oxides. The surface electronic properties of these added photocatalytic centers, as well as junctions, are central to applications in photocatalysis. Main goals of the work are to understand ultrafast photoinduced processes of charge localization at the surface of photocatalytic materials and the transport of charge across junctions. To address these questions, XUV core level photoemission spectroscopy and transient absorption-reflectivity spectroscopy are employed, with pump probe methods using femtosecond and attosecond XUV laser pulses. Understanding ultrafast photoinduced processes at surfaces and junctions is a defining principle that can guide advances in the next generation of catalysts to produce storable fuels from sustainable inputs for the Air Force. The progress report discusses results for semiconductor semiconductor interfaces (Si-TiO2), Schottky barriers, i.e. metal films on semiconductors (Si-Zn), metal cluster decoration of semiconductors and the size dependent transition to metallicity (Zn clusters on Si).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 14, 2022
- Source ID
- FA95501910314
Entities
People
- Stephen R. Leone
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of California Regents