The ability to follow electron dynamics at surfaces is necessary to identify the material properties and surface carrier trapping, which mediate carrier lifetime and ultimately determine energy conversion efficiency. Toward this goal we have recently developed extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy as a surface specific analog of XUV transient absorption. This technique extends the benefits of element specific x-ray absorption spectroscopy to the study of surface electron dynamics by measuring core-hole resonances with a probe depth of less than 3 nm and a time resolution of less than 100 fs. For an example, using XUV-RA, we provide a systematic comparison between surface and bulk polaron formation kinetics and energetics in photoexcited hematite. Small polaron formation is known to limit the photocatalytic charge transport efficiency of hematite via ultrafast carrier self-trapping. While small polaron formation is known to occur in bulk hematite, a complete description of surface polaron formation in this material is not fully understood. We find that the rate of surface polaron formation (250 ± 40 fs) is about three times slower than bulk polaron formation (90 ± 5 fs) in photoexcited hematite. Additionally, we show that the surface polaron formation rate can be systematically tuned by surface molecular functionalization. The ability to tune the kinetics and energetics of polaron formation and hopping by molecular functionalization provides the unique opportunity to synthetically control electron transport in hematite.<br/>

Achieving surface sensitivity in ultrafast XUV spectroscopy: Probing surface electron dynamics in hematite photoanode

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.