Built-In Potential in Fe ₂ O ₃ -Cr ₂ O ₃ Superlattices for Improved Photoexcited Carrier Separation

Journal Article · Thu Dec 17 04:00:00 EST 2015 · Advanced Materials

DOI:https://doi.org/10.1002/adma.201504545· OSTI ID:1252837

Kaspar, Tiffany C. ^[1]; Schreiber, Daniel K. ^[2]; Spurgeon, Steven R. ^[1]; McBriarty, Martin E. ^[1]; Carroll, Gerard M. ^[3]; Gamelin, Daniel R. ^[3]; Chambers, Scott A. ^[1]

---

1. Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99354 USA
2. Energy and Environment Directorate, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99354 USA
3. Department of Chemistry, University of Washington, P.O. Box 1700 Seattle WA 98195-1700 USA

We demonstrate that the different surface terminations exhibited by α-Fe2O3 (hematite) and α-Cr2O3 (eskolaite) in superlattices (SL) of these materials, synthesized with exquisite control by molecular beam epitaxy, determine the heterojunction interface structure and result in controllable, non-commutative band offset values. Precise atomic control of the interface structure allowed us to vary the valence band offset from 0.35 eV to 0.79 eV. This controllable band alignment can be harnessed to generate a built-in potential in Fe2O3-Cr2O3 SLs. For instance, in a 2.5-period SL, a built-in potential of 0.8 eV was realized as measured by x-ray photoelectron spectroscopy of Ti dopants as probe species. The high quality of the SL structure was confirmed by atom probe tomography and scanning transmission electron microscopy. Enhanced photocurrents were measured for a thick Fe2O3 epitaxial film capped with an (Fe2O3)3-(Cr2O3)3 SL; this enhancement was attributed to efficient electron-hole separation in the SL as a result of the band alignment. The Fe-O-Cr bonds at the SL interfaces also red-shifted the onset of photoconductivity to ~1.6 eV. Exploiting the band alignment and photoabsorption properties of Fe2O3-Cr2O3 SLs has the potential to increase the efficiency of hematite-based photoelectrochemical water splitting.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1252837
• Report Number(s): PNNL-SA-112959; 48341; KC0203020
• Journal Information: Advanced Materials, Journal Name: Advanced Materials Journal Issue: 8 Vol. 28; ISSN 0935-9648
• Publisher: Wiley
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory
Hematite
N06266
photoconductivity
potential
superlattices
x-ray photoelectron spectroscopy