Elucidating the Mechanism of Charge Transfer and Transport at Surfaces Using Ultrafast XUV Spectroscopy
Abstract
Direct observation of charge transfer and trapping at interfaces will provide important understanding of the surface properties that determine efficiency during energy conversion catalysis. In these experiments, we will investigate the coupling of photoexcited carriers with surface phonon modes in order to show that carrier self trapping at surfaces rather than defect states are often responsible for poor interfacial carrier dynamics. Validating this hypothesis by direct, real time observation of surface electron dynamics will inform new transformative approaches for controlling the transport properties in this important class of earth abundant solar catalysts. To enable these studies, we have constructed an ultrafast extreme ultraviolet (XUV) light source based on high harmonic generation. Reflection–absorption spectroscopy using this source combines the benefits of X ray absorption, such as element and oxidation state specificity, with surface sensitivity and ultrafast time resolution, having a measured probe depth of only a few nm and an instrument response less than 100 fs. Combining XUV measurements with sum frequency generation vibrational spectroscopy, we will investigate the dynamics of small polaron formation at surfaces and the molecular properties of an interface, which mediate these dynamics. Covalently anchored phenol ligands will serve as well controlled hole acceptors on an oxide surface, where trap state energy and surface dipole can be independently tuned by aromatic substitutions. Using these model surfaces, we will study the role of coherent coupling between photoexcited free carriers and surface phonons by measuring optically driven quantum coherences at the phonon frequencies of these materials. Spectroscopic measurements will be complimented by performance testing of these materials as catalysts for photo electrochemical water splitting and CO2 reduction. Using this combination of approaches, we expect to demonstrate that accurate understanding
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 14, 2022
- Source ID
- FA95501910184
Entities
People
- Lawrence Baker
Organizations
- Air Force Office of Scientific Research
- Ohio State University
- United States Air Force