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Large work function reduction by adsorption of a molecule with a negative electron affinity: Pyridine on ZnO(10-10)

MPS-Authors
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Hofmann,  Oliver T.
Theory, Fritz Haber Institute, Max Planck Society;

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Deinert,  Jan-Christoph
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Xu,  Yong
Theory, Fritz Haber Institute, Max Planck Society;

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Rinke,  Patrick
Theory, Fritz Haber Institute, Max Planck Society;

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Stähler,  Julia
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Wolf,  Martin
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Scheffler,  Matthias
Theory, Fritz Haber Institute, Max Planck Society;

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Citation

Hofmann, O. T., Deinert, J.-C., Xu, Y., Rinke, P., Stähler, J., Wolf, M., et al. (2013). Large work function reduction by adsorption of a molecule with a negative electron affinity: Pyridine on ZnO(10-10). The Journal of Chemical Physics, 139(17): 174701. doi:10.1063/1.4827017.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0014-633E-3
Abstract
Using thermal desorption and photoelectron spectroscopy to study the adsorption of pyridine on ZnO(10-10), we find that the work function is significantly reduced from 4.5 eV for the bare ZnO surface to 1.6 eV for one monolayer of adsorbed pyridine. Further insight into the interface morphology and binding mechanism is obtained using density functional theory. Although semilocal density functional theory provides unsatisfactory total work functions, excellent agreement of the work function changes is achieved for all coverages. In a closed monolayer, pyridine is found to bind to every second surface Zn atom. The strong polarity of the Zn-pyridine bond and the molecular dipole moment act cooperatively, leading to the observed strong work function reduction. Based on simple alignment considerations, we illustrate that even larger work function modifications should be achievable using molecules with negative electron affinity. We expect the application of such molecules to significantly reduce the electron injection barriers at ZnO/organic heterostructures.