Chromium-doped SrTiO 3 nanocrystals of perovskite structure type and 45 nm (±15 nm) edge lengths were obtained by hydrothermal synthesis in water from titanium oxide, strontium hydroxide, and chromium( iii ) nitrate. According to XPS, the majority of the surface chromium (68.3%) is present in the 3+ state and the remainder (32.2%) in the 6+ state. Optical spectroscopy confirms a broad absorption at 2.3–2.9 eV from Cr(3+) dopant states, in addition to the 3.2 eV band edge of the SrTiO 3 host. After modification with Pt nanoparticles, Cr-doped SrTiO 3 nanocrystals catalyze photochemical H 2 evolution from aqueous methanol under visible light illumination (>400 nm) and with an apparent quantum yield of 0.66% at 435 nm. According to surface photovoltage spectroscopy (SPS), Cr-doped SrTiO 3 nanocrystals deposited onto gold substrates are n-type and have an effective band gap of 1.75 eV. SPS and transient illumination experiments at 2.50 eV reveal an anomalous surface photovoltage that increases with prior light exposure to values of up to −6.3 V. This photovoltage is assigned to ferroelectric polarization of the material in the space charge layer at the Au/SrTiO 3 :Cr interface. The polarization is stable for 24 h in vacuum but disappears after 12 h when samples are stored in air. The electric polarizability of SrTiO 3 :Cr is confirmed when films are exposed to static electric fields (1.20 MV m −1 ) in a fixed capacitor configuration. The discovery of a ferroelectric effect in Cr-doped SrTiO 3 could be significant for the development of improved photocatalysts for the conversion of solar energy into fuel.
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Probing electronic dead layers in homoepitaxial n -SrTiO 3 (001) films
We combine state-of-the-art oxide epitaxial growth by hybrid molecular beam epitaxy with transport, x-ray photoemission, and surface diffraction, along with classical and first-principles quantum mechanical modeling to investigate the nuances of insulating layer formation in otherwise high-mobility homoepitaxial n-SrTiO 3 (001) films. Our analysis points to charge immobilization at the buried n-SrTiO 3 /undoped SrTiO 3 (001) interface as well as within the surface contamination layer resulting from air exposure as the drivers of electronic dead-layer formation. As Fermi level equilibration occurs at the surface and the buried interface, charge trapping reduces the sheet carrier density ( n 2 D ) and renders the n-STO film insulating if n 2 D falls below the critical value for the metal-to-insulator transition.
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- Award ID(s):
- 2011401
- PAR ID:
- 10411282
- Date Published:
- Journal Name:
- APL Materials
- Volume:
- 10
- Issue:
- 7
- ISSN:
- 2166-532X
- Page Range / eLocation ID:
- 070903
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0098500
