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Orientation dependent ionization potential of In2O3: A natural source for inhomogeneous barrier formation at electrode interfaces in organic electronics

Hohmann, Mareike V. and Ágoston, Péter and Wachau, André and Bayer, Thorsten J. M. and Broetz, Joachim and Albe, Karsten and Klein, Andreas (2011):
Orientation dependent ionization potential of In2O3: A natural source for inhomogeneous barrier formation at electrode interfaces in organic electronics.
In: Journal of Physics: Condensed Matter, IOP Publishing, p. 334203, 23, (33), ISSN 0953-8984, [Online-Edition: http://dx.doi.org/10.1088/0953-8984/23/33/334203],
[Article]

Abstract

The ionization potentials of In2O3 films grown epitaxially by magnetron sputtering on Y-stabilized ZrO2 substrates with (100) and (111) surface orientation are determined using photoelectron spectroscopy. Epitaxial growth is verified using x-ray diffraction. The observed ionization potentials, which directly affect the work functions, are in good agreement with ab initio calculations using density functional theory. While the (111) surface exhibits a stable surface termination with an ionization potential of ~ 7.0 eV, the surface termination and the ionization potential of the (100) surface depend strongly on the oxygen chemical potential. With the given deposition conditions an ionization potential of ~ 7.7 eV is obtained, which is attributed to a surface termination stabilized by oxygen dimers. This orientation dependence also explains the lower ionization potentials observed for In2O3 compared to Sn-doped In2O3 (ITO) (Klein et al 2009 Thin Solid Films 518 1197–203). Due to the orientation dependent ionization potential, a polycrystalline ITO film will exhibit a laterally varying work function, which results in an inhomogeneous charge injection into organic semiconductors when used as electrode material. The variation of work function will become even more pronounced when oxygen plasma or UV–ozone treatments are performed, as an oxidation of the surface is only possible for the (100) surface. The influence of the deposition technique on the formation of stable surface terminations is also discussed.

Item Type: Article
Erschienen: 2011
Creators: Hohmann, Mareike V. and Ágoston, Péter and Wachau, André and Bayer, Thorsten J. M. and Broetz, Joachim and Albe, Karsten and Klein, Andreas
Title: Orientation dependent ionization potential of In2O3: A natural source for inhomogeneous barrier formation at electrode interfaces in organic electronics
Language: English
Abstract:

The ionization potentials of In2O3 films grown epitaxially by magnetron sputtering on Y-stabilized ZrO2 substrates with (100) and (111) surface orientation are determined using photoelectron spectroscopy. Epitaxial growth is verified using x-ray diffraction. The observed ionization potentials, which directly affect the work functions, are in good agreement with ab initio calculations using density functional theory. While the (111) surface exhibits a stable surface termination with an ionization potential of ~ 7.0 eV, the surface termination and the ionization potential of the (100) surface depend strongly on the oxygen chemical potential. With the given deposition conditions an ionization potential of ~ 7.7 eV is obtained, which is attributed to a surface termination stabilized by oxygen dimers. This orientation dependence also explains the lower ionization potentials observed for In2O3 compared to Sn-doped In2O3 (ITO) (Klein et al 2009 Thin Solid Films 518 1197–203). Due to the orientation dependent ionization potential, a polycrystalline ITO film will exhibit a laterally varying work function, which results in an inhomogeneous charge injection into organic semiconductors when used as electrode material. The variation of work function will become even more pronounced when oxygen plasma or UV–ozone treatments are performed, as an oxidation of the surface is only possible for the (100) surface. The influence of the deposition technique on the formation of stable surface terminations is also discussed.

Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 23
Number: 33
Publisher: IOP Publishing
Uncontrolled Keywords: electrical, magnetic and optical Surfaces; interfaces and thin films
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science > Surface Science
11 Department of Materials and Earth Sciences > Material Science > Physics of Surfaces
11 Department of Materials and Earth Sciences > Material Science > Structure Research
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue > D - Component properties
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue > D - Component properties > Subproject D3: Function and fatigue of oxide electrodes in organic light emitting diodes
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Zentrale Einrichtungen
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres
DFG-Collaborative Research Centres (incl. Transregio)
Date Deposited: 17 Sep 2012 12:59
Official URL: http://dx.doi.org/10.1088/0953-8984/23/33/334203
Additional Information:

SFB 595 D3

Identification Number: doi:10.1088/0953-8984/23/33/334203
Funders: This work was supported by the Deutsche Forschungsgemeinschaft (DFG) within the collaborative research center SFB 595 (Electrical Fatigue of Functional Materials).
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