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Title: Thermal stability of nitrogen-doped SrTiO{sub 3} films: Electronic and optical properties studies

Abstract

The thermal stability of nitrogen-doped SrTiO{sub 3} (001) films in terms of electronic and optical properties has been studied by using x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry techniques. The chemical states of nitrogen in nitrogen-doped SrTiO{sub 3} films include both substitutional and interstitial states. The N 2p states localized above the O 2p-derived valence band maximum are attributed to the change of optical properties. Postannealing will induce the valence band edge shift due to the thermal instability of interstitial N states, which may degrade the photocatalysis of nitrogen-doped SrTiO{sub 3} films during applications.

Authors:
; ; ; ; ; ;  [1];  [2];  [3];  [3];  [3];  [3]
  1. Department of Physics, National University of Singapore, Singapore 117542 (Singapore)
  2. (United States)
  3. (Singapore)
Publication Date:
OSTI Identifier:
20982763
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 6; Other Information: DOI: 10.1063/1.2713350; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ANNEALING; CHEMICAL STATE; DOPED MATERIALS; ELLIPSOMETRY; INTERSTITIALS; NITROGEN; OPTICAL PROPERTIES; PHOTOCATALYSIS; PHOTOCHEMISTRY; PHOTOEMISSION; STRONTIUM TITANATES; THIN FILMS; X-RAY PHOTOELECTRON SPECTROSCOPY; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Mi, Y. Y., Yu, Z., Wang, S. J., Gao, X. Y., Wee, A. T. S., Ong, C. K., Huan, C. H. A., Freescale Semiconductor Inc., Tempe, Arizona 85284, Institute of Materials Research and Engineering, Singapore 117602, Department of Physics, National University of Singapore, Singapore 117542, Institute of Materials Research and Engineering, Singapore 117602, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technology University, Singapore 637616. Thermal stability of nitrogen-doped SrTiO{sub 3} films: Electronic and optical properties studies. United States: N. p., 2007. Web. doi:10.1063/1.2713350.
Mi, Y. Y., Yu, Z., Wang, S. J., Gao, X. Y., Wee, A. T. S., Ong, C. K., Huan, C. H. A., Freescale Semiconductor Inc., Tempe, Arizona 85284, Institute of Materials Research and Engineering, Singapore 117602, Department of Physics, National University of Singapore, Singapore 117542, Institute of Materials Research and Engineering, Singapore 117602, & Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technology University, Singapore 637616. Thermal stability of nitrogen-doped SrTiO{sub 3} films: Electronic and optical properties studies. United States. doi:10.1063/1.2713350.
Mi, Y. Y., Yu, Z., Wang, S. J., Gao, X. Y., Wee, A. T. S., Ong, C. K., Huan, C. H. A., Freescale Semiconductor Inc., Tempe, Arizona 85284, Institute of Materials Research and Engineering, Singapore 117602, Department of Physics, National University of Singapore, Singapore 117542, Institute of Materials Research and Engineering, Singapore 117602, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technology University, Singapore 637616. Thu . "Thermal stability of nitrogen-doped SrTiO{sub 3} films: Electronic and optical properties studies". United States. doi:10.1063/1.2713350.
@article{osti_20982763,
title = {Thermal stability of nitrogen-doped SrTiO{sub 3} films: Electronic and optical properties studies},
author = {Mi, Y. Y. and Yu, Z. and Wang, S. J. and Gao, X. Y. and Wee, A. T. S. and Ong, C. K. and Huan, C. H. A. and Freescale Semiconductor Inc., Tempe, Arizona 85284 and Institute of Materials Research and Engineering, Singapore 117602 and Department of Physics, National University of Singapore, Singapore 117542 and Institute of Materials Research and Engineering, Singapore 117602 and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technology University, Singapore 637616},
abstractNote = {The thermal stability of nitrogen-doped SrTiO{sub 3} (001) films in terms of electronic and optical properties has been studied by using x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry techniques. The chemical states of nitrogen in nitrogen-doped SrTiO{sub 3} films include both substitutional and interstitial states. The N 2p states localized above the O 2p-derived valence band maximum are attributed to the change of optical properties. Postannealing will induce the valence band edge shift due to the thermal instability of interstitial N states, which may degrade the photocatalysis of nitrogen-doped SrTiO{sub 3} films during applications.},
doi = {10.1063/1.2713350},
journal = {Journal of Applied Physics},
number = 6,
volume = 101,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • The nitrogen-doping induced changes in optical properties and electronic structures of SrTiO{sub 3} films have been investigated by using spectroscopic ellipsometry and x-ray photoemission spectroscopy. Combined with the first-principles calculations, it is found that the localized N 2p states above O 2p states are attributed to the new absorption edge at 500 nm and the photoactivity in the visible light region. Our results are consistent with both recent experimental and theoretical studies on nitrogen-doped TiO{sub 2}, where the visible light responses arise from the localized N 2p states slightly above the valence-band edge rather than the band gap narrowing.
  • The structural, optical, and room-temperature electrical properties of strained La-doped SrTiO{sub 3} epitaxial thin films are investigated. Conductive La-doped SrTiO{sub 3} thin films with concentration varying from 5 to 25% are grown by molecular beam epitaxy on four different substrates: LaAlO{sub 3}, (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7}, SrTiO{sub 3}, and DyScO{sub 3}, which result in lattice mismatch strain ranging from −2.9% to +1.1%. We compare the effect of La concentration and strain on the structural and optical properties, and measure their effect on the electrical resistivity and mobility at room temperature. Room temperature resistivities ranging from ∼10{sup −2} tomore » 10{sup −5} Ω cm are obtained depending on strain and La concentration. The room temperature mobility decreases with increasing strain regardless of the sign of the strain. The observed Drude peak and Burstein-Moss shift from spectroscopic ellipsometry clearly confirm that the La addition creates a high density of free carriers in SrTiO{sub 3}. First principles calculations were performed to help understand the effect of La-doping on the density of states effective mass as well as the conductivity and DC relaxation time.« less
  • Highlights: • Er/N co-doped SrTiO{sub 3} was prepared by a solvothermal process at low temperature. • The co-doping induces the band gap narrowing and prominent absorbance in visible light region. • The samples show excellent catalytic activity and stability under visible light irradiation. - Abstract: Erbium–nitrogen co-doped SrTiO{sub 3} photocatalysts have been synthesized by a facile solvothermal method. The resulting samples were analyzed by FE-SEM, XRD, BET-surface area and UV–vis. The UV–vis absorption spectra of these powders indicated that erbium–nitrogen co-doped SrTiO{sub 3} possessed stronger absorption bands in the visible light region in comparison with that of pure SrTiO{sub 3}.more » The occurrence of the erbium–nitrogen co-doped cubic SrTiO{sub 3} induced the higher photocatalytic activities for the degradation of methyl orange (MO) under irradiation by ultraviolet light and visible light, respectively, being superior to that of pure SrTiO{sub 3} and commercial TiO{sub 2} (P-25) powders. In addition, the Er–N co-doped SrTiO{sub 3} (initial molar ratios of Sr/Er/N = 1:0.015:0.1, designated as S5) sample showed the best photocatalytic activity with the degradation rate as high as 98% after 30 min under the visible light irradiation. After five cycles, the photocatalytic activity of the S5 catalyst showed no significant decrease, which indicated that the photocatalysts were stable under visible light irradiation.« less
  • We have used the linear muffin-tin-orbital method, without geometrical approximations, to calculate the electronic structure of tetragonal BaTiO{sub 3} and cubic SrTiO{sub 3}. Using our self-consistent potential, we have calculated the frequency-dependent dielectric function and the reflectivity spectrum. For tetragonal BaTiO{sub 3} the anisotropic optical properties are calculated. We compare our calculations with experimental data and find good agreement. We analyze the origin of the different calculated features in the optical spectra by means of our energy-band structure. {copyright} 2001 American Institute of Physics.
  • We investigated infrared-active phonons of CaTiO3, SrTiO3, BaTiO3, and Ba0.5Sr0.5TiO3 thin films, and a (BaTiO3)5/(SrTiO3)5 artificial superlattice by a Fourier transform infrared spectrometer with a grazing angle (48{sup o}) incident reflectance method. The longitudinal phonon energies of the thin films were different from those of the bulk material due to the lattice strain of the substrate. The Ba0.5Sr0.5TiO3 thin film and (BaTiO3)5/(SrTiO3)5 superlattice showed different phonon modes due to structural discrepancies, even though their chemical compositions are similar. The Ba0.5Sr0.5TiO3 thin film showed a single phonon energy lying between the phonon energies of BaTiO3 and SrTiO3 thin films, while themore » (BaTiO3)5/(SrTiO3)5 superlattice well preserved the characteristic phonon modes of BaTiO3 and SrTiO3 thin films.« less