Abstract
Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter’s dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti3+ centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides.
Highlights
“large polaron” (~40 meV below EF) was reported
Low temperature (LT) electron paramagnetic resonance (EPR) studies on powdered anatase TiO2 under continuous UV irradiation, showed the appearance of two distinct traces attributed to electrons trapped at paramagnetic Ti3+ sites, whose geometry remained unspecified[11]
The nature of the photoinduced electron traps was addressed in recent theoretical studies of the photoinduced small polarons in anatase TiO214, which predicted that for the bulk, an ~80% charge localization occurs at Ti3+ ions
Summary
“large polaron” (~40 meV below EF) was reported. The small polaron formation was attributed to pentacoordinated Ti3+ centres, due to the presence of an Ovac[4,6,7].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
