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Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe_2O_3

Carneiro, Lucas M. and Cushing, Scott K. and Liu, Chong and Su, Yude and Yang, Peidong and Alivisatos, A. Paul and Leone, Stephen R. (2017) Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe_2O_3. Nature Materials, 16 (8). pp. 819-825. ISSN 1476-1122. https://resolver.caltech.edu/CaltechAUTHORS:20180627-105307959

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Abstract

Small polaron formation is known to limit ground-state mobilities in metal oxide photocatalysts. However, the role of small polaron formation in the photoexcited state and how this affects the photoconversion efficiency has yet to be determined. Here, transient femtosecond extreme-ultraviolet measurements suggest that small polaron localization is responsible for the ultrafast trapping of photoexcited carriers in haematite (α-Fe_2O_3). Small polaron formation is evidenced by a sub-100 fs splitting of the Fe 3p core orbitals in the Fe M_(2,3) edge. The small polaron formation kinetics reproduces the triple-exponential relaxation frequently attributed to trap states. However, the measured spectral signature resembles only the spectral predictions of a small polaron and not the pre-edge features expected for mid-gap trap states. The small polaron formation probability, hopping radius and lifetime varies with excitation wavelength, decreasing with increasing energy in the t_(2g) conduction band. The excitation-wavelength-dependent localization of carriers by small polaron formation is potentially a limiting factor in haematite’s photoconversion efficiency.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1038/nmat4936DOIArticle
https://rdcu.be/11PrPublisherFree ReadCube access
ORCID:
AuthorORCID
Cushing, Scott K.0000-0003-3538-2259
Alivisatos, A. Paul0000-0001-6895-9048
Leone, Stephen R.0000-0003-1819-1338
Alternate Title:Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3
Additional Information:© 2017 Macmillan Publishers Limited. Received 17 January 2017; accepted 26 May 2017; published online 10 July 2017. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05-CH11231 within the Physical Chemistry of Inorganic Nanostructures Program (KC3103). S.K.C. acknowledges support by the Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) Postdoctoral Research Award under the EERE Solar Energy Technologies Office. Author Contributions: L.M.C., S.K.C. and S.R.L. designed the study. L.M.C. and S.K.C. performed the transient XUV measurements and data analysis. S.K.C. modelled the polaron spectral signature and dynamics. C.L. and Y.S. were responsible for sample fabrication and characterization. L.M.C., S.K.C., C.L., Y.S., P.Y., A.P.A. and S.R.L. wrote and revised the manuscript. Data availability: The source data necessary to support the findings of this paper are available from the corresponding author upon request. The authors declare no competing financial interests.
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-05-CH11231
Issue or Number:8
Record Number:CaltechAUTHORS:20180627-105307959
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180627-105307959
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87393
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:27 Jun 2018 20:33
Last Modified:03 Oct 2019 19:55

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