Observation of filled states at the Fermi-level in alkali-metal intercalated organic films: dependence on substrate work function

We present ultraviolet photoelectron spectroscopy studies on alkali metal-intercalated thin films of electroluminescent p-sexiphenyl (6P) and the organic hole transporting material N, N′-bis-(1-naphthyl)- N, N′-diphenyl1-1,1-biphenyl1-4,4′-diamine (α-NPD). The formation of new occupied electronic st...

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Bibliographic Details
Published in:Journal of electron spectroscopy and related phenomena 2005-06, Vol.144 (Complete), p.495-498
Main Authors: Koch, N., Jäckel, F., Ghijsen, J., Rojas, M.C., Grioni, M., Rabe, J.P., Johnson, R.L., Kahn, A., Pireaux, J.-J.
Format: Article
Language:English
Subjects:
Alkali metals
Organic materials
Photoelectron spectroscopy
Thin films
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Summary:We present ultraviolet photoelectron spectroscopy studies on alkali metal-intercalated thin films of electroluminescent p-sexiphenyl (6P) and the organic hole transporting material N, N′-bis-(1-naphthyl)- N, N′-diphenyl1-1,1-biphenyl1-4,4′-diamine (α-NPD). The formation of new occupied electronic states in the otherwise empty energy gap of 6P and α-NPD is observed, accompanied by a significant shift of the Fermi-level. Depending on the work function ϕ of the substrate used for the organic thin films, we observe two different scenarios at low intercalation levels: the new electronic states are observed at (and even above) E F for high ϕ substrates, whereas they are observed below E F for low ϕ substrates. At high intercalation levels, all the states are observed below E F. The observation of states at and above E F is attributed to a lack of thermodynamic equilibrium across the organic thin film.
ISSN:0368-2048
1873-2526
DOI:10.1016/j.elspec.2005.01.016