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Band Gap Reduction

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Peter V Sushko – 1st expert on this subject based on the ideXlab platform

  • Band Gap Reduction and dopant interaction in epitaxial la cr co doped srtio3 thin films
    Chemistry of Materials, 2014
    Co-Authors: Ryan B Comes, Peter V Sushko, Steve M Heald, Robert J Colby, Mark E Bowden, Scott A Chambers

    Abstract:

    We show that by co-doping SrTiO3 (STO) epitaxial thin films with equal amounts of La and Cr, it is possible to produce films with an optical Band Gap ∼0.9 eV lower than that of undoped STO. Sr1–xLaxTi1–xCrxO3 thin films were deposited by molecular beam epitaxy and characterized using X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy to show that the Cr dopants are almost exclusively in the Cr3+ oxidation state. Extended X-ray absorption fine structure measurements and theoretical modeling suggest that it is thermodynamically preferred for La and Cr dopants to occupy nearest-neighbor A- and B-sites in the lattice. Transport measurements show that the material exhibits variable-range hopping conductivity with high resistivity. These results create new opportunities for the use of doped STO films in photovoltaic and photocatalytic applications.

  • optical absorption and Band Gap Reduction in fe1 xcrx 2o3 solid solutions a first principles study
    Journal of Physical Chemistry C, 2013
    Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V Sushko

    Abstract:

    We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.

  • Optical Absorption and Band Gap Reduction in (Fe1–xCrx)2O3 Solid Solutions: A First-Principles Study
    Journal of Physical Chemistry C, 2013
    Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V Sushko

    Abstract:

    We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.

Viktor N Staroverov – 2nd expert on this subject based on the ideXlab platform

  • Band Gap Reduction in zno and zns by creating layered zno zns heterostructures
    Journal of Physical Chemistry Letters, 2015
    Co-Authors: Amin Torabi, Viktor N Staroverov

    Abstract:

    Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.

  • Band Gap Reduction in ZnO and ZnS by Creating Layered ZnO/ZnS Heterostructures
    Journal of Physical Chemistry Letters, 2015
    Co-Authors: Amin Torabi, Viktor N Staroverov

    Abstract:

    Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.

Scott A Chambers – 3rd expert on this subject based on the ideXlab platform

  • Band Gap Reduction and dopant interaction in epitaxial la cr co doped srtio3 thin films
    Chemistry of Materials, 2014
    Co-Authors: Ryan B Comes, Peter V Sushko, Steve M Heald, Robert J Colby, Mark E Bowden, Scott A Chambers

    Abstract:

    We show that by co-doping SrTiO3 (STO) epitaxial thin films with equal amounts of La and Cr, it is possible to produce films with an optical Band Gap ∼0.9 eV lower than that of undoped STO. Sr1–xLaxTi1–xCrxO3 thin films were deposited by molecular beam epitaxy and characterized using X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy to show that the Cr dopants are almost exclusively in the Cr3+ oxidation state. Extended X-ray absorption fine structure measurements and theoretical modeling suggest that it is thermodynamically preferred for La and Cr dopants to occupy nearest-neighbor A- and B-sites in the lattice. Transport measurements show that the material exhibits variable-range hopping conductivity with high resistivity. These results create new opportunities for the use of doped STO films in photovoltaic and photocatalytic applications.

  • optical absorption and Band Gap Reduction in fe1 xcrx 2o3 solid solutions a first principles study
    Journal of Physical Chemistry C, 2013
    Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V Sushko

    Abstract:

    We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.

  • Optical Absorption and Band Gap Reduction in (Fe1–xCrx)2O3 Solid Solutions: A First-Principles Study
    Journal of Physical Chemistry C, 2013
    Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V Sushko

    Abstract:

    We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.