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

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
   

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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.
   

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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).
   

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

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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.
   

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6. Goal and Methods
   

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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).
   

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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).
   

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

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

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

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

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

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

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

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

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

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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
    ∝
    

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

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20. Frontier Orbitals (n = 4)
    HOMO LUMO
    

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21. Frontier Orbitals (n = 6)
    HOMO LUMO
    

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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
    

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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).
    

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24. Bonus Slides
    

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25. Interatomic Potential: In2
    O3
    • Anion Frenkel Formation
    

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26. TCO Applications
    Source: Nikkei Electronics Asia
    

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27. Nanocluster Paper
    

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