$30 off During Our Annual Pro Sale. View Details »

Global and local minimum structures for clusters of In2O3

Aron Walsh
November 11, 2009

Global and local minimum structures for clusters of In2O3

A presentation delivered at the annual CCP5 meeting (November 2009 in London) on indium oxide nanoclusters. Later published in http://pubs.rsc.org/en/Content/ArticleLanding/2010/CP/c0cp00056f#!divAbstract

Aron Walsh

November 11, 2009
Tweet

More Decks by Aron Walsh

Other Decks in Science

Transcript

  1. Aron Walsh, Richard Catlow, Alexey Sokol and Scott Woodley
    Materials Chemistry, Department of Chemistry,
    University College London
    Global and Local Minimum Structures for Clusters of
    Indium Sesquioxide

    View Slide

  2. Transparent Conducting Oxides
    Combine optical transparency with electronic conductivity
    > 3 eV
    EF
    n-type:
    In2
    O3
    , SnO2
    , ZnO
    In2
    O3
    :Sn, SnO2
    :F, ZnO:Al
    p-type:
    CuAlO2
    , SrCu2
    O2
    CuAlO2
    :Mg, SrCu2
    O2
    :Ca
    Applications:
    Flat-panel displays, organic and inorganic solar cells,
    organic light-emitting diodes, transparent displays,
    chemical sensors, smart windows.

    View Slide

  3. Reduce Indium Dependence
    • Lower Cost
    • Increase Stability
    • Optoelectronic Control
    • Parent Binary Oxides: ZnO, In2
    O3
    , Al2
    O3
    , Ga2
    O3
    , SnO2
    • Electronic Band Gaps: Al >> Ga > Sn > Zn > In
    • Resistivity: Al >> Ga > Sn > Zn > In
    In2
    O3
    (ZnO)
    In2
    O3
    (ZnO)3
    In2
    O3
    (ZnO)5
    A. Walsh et al. Phys. Rev. B 79, 073105 (2009).

    View Slide

  4. Nanostructures
    • An alternative approach to reduce indium usage.

    View Slide

  5. Goal and Methods
    • Derive robust interatomic In2
    O3
    potential.
    Explore high pressure behaviour.
    • Determine lowest energy structures formed from
    stoichiometric building blocks: (In2
    O3
    )n
    n = 1 – 7
    Global optimization: Evolutionary algorithm (GULP).
    • Validate and characterize using a first-principles method.
    Density functional theory calculations (VASP).
    • Assess structural trends, stability and optoelectronic
    properties.

    View Slide

  6. Goal and Methods

    View Slide

  7. Indium Sesquioxide
    • Crystal Structure: Cubic bixbyite lattice (80 atom cell).
    • Band Gap: Fundamental 2.9 eV1; optical > 3.5 eV.
    • Conductivity: Oxygen deficient; intrinsically n-type.
    1A. Walsh et al. Phys. Rev. Lett. 100, 167402 (2008).

    View Slide

  8. Interatomic Potential: In2
    O3
    6
    exp
    i j ij
    ij
    ij ij
    q q r C
    U A
    r r
    ρ
    ⎛ ⎞
    = + − −
    ⎜ ⎟
    ⎝ ⎠
    Property Experiment Literature
    Potential1
    Sokol
    Potential2
    LDA-DFT
    a (Å) 10.117 10.120 10.121 10.094
    B (GPa) 194.24 222.79 193.77 174
    ε0
    8.9-9.5 6.87 9.05
    ε∞
    4.0 3.53 3.90 3.82
    • Buckingham potential with shell polarization on oxygen.
    1O. Warschkow et al., J. Am. Ceram. Soc. 86, 1700 (2003).
    2A. Walsh et al, Chemistry of Materials 21, 4962 (2009).

    View Slide

  9. Interatomic Potential: In2
    O3
    • Reproduces high pressure phase stabilities.

    View Slide

  10. Clusters: n = 1
    0.00 eV (C2v
    )
    0.11 eV (D∞
    )
    0.49 eV (C2v
    ) 1.69 eV (D3h
    )

    View Slide

  11. Clusters: n = 2
    0.00 eV (C2h
    )
    1.04 eV (Td
    ) 1.22 eV (D2h
    )
    1.20 eV (C2v
    )

    View Slide

  12. Clusters: n = 3
    0.60 eV (C2v
    )
    0.00 eV (C2s
    )
    1.53 eV (D3h
    )

    View Slide

  13. Clusters: n = 4
    1.16 eV (C2v
    )
    0.00 eV (D3d
    )
    3.84 eV (Oh
    )

    View Slide

  14. Clusters: n = 5
    0.30 eV (C2
    )
    0.00 eV (C1
    )
    4.60 eV (D5h
    )

    View Slide

  15. Clusters: n = 6
    6.06 eV (D6h
    )
    0.00 eV (C1
    )
    0.42 eV (D3d
    )

    View Slide

  16. Clusters: n = 7
    0.35 eV (D3
    )
    0.10 eV (C1
    )
    0.00 eV (C1
    )

    View Slide

  17. Nanoclusters: n = 1 - 7
    1. C2v
    2. C2h
    3. C2s
    4. D3d
    5. C1
    6. C1
    7. C1

    View Slide

  18. Cluster Stability
    0
    2
    4
    6
    8
    1 2 3 4 5 6 7
    Energy (eV per n)
    (In2
    O3
    )n
    1
    E
    n

    View Slide

  19. Frontier Orbitals (n = 1, 2)
    n = 1 n = 2
    HOMO LUMO HOMO LUMO

    View Slide

  20. Frontier Orbitals (n = 4)
    HOMO LUMO

    View Slide

  21. Frontier Orbitals (n = 6)
    HOMO LUMO

    View Slide

  22. Frontier Orbital Separation
    -7
    -6
    -5
    -4
    1 2 3 4 5 6 7
    GGA HOMO-LUMO Levels (eV )
    (In2
    O3
    )n
    HOMO
    LUMO

    View Slide

  23. Conclusion
    • Presented a new In2
    O3
    interatomic potential that
    describes bulk and cluster properties.
    • n < 4 clusters have distinct symmetric global minima.
    • n > 4 clusters tend towards bulk-like, low symmetry
    particles.
    • Open framework clusters have high energetic cost.
    • HOMO and LUMO character is consistent with bulk.
    Future work:
    • Extend to higher n.
    • Explore excited state properties.
    Acknowledgements: Materials Chemistry Consortium
    (Access to Hector); EU FP7 (Marie Curie Fellowship).

    View Slide

  24. Bonus Slides

    View Slide

  25. Interatomic Potential: In2
    O3
    • Anion Frenkel Formation

    View Slide

  26. TCO Applications
    Source: Nikkei Electronics Asia

    View Slide

  27. Nanocluster Paper

    View Slide