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Interface formation of metals and poly( p ‐phenylene vinylene): surface species and band bending
Author(s) -
Ettedgui E.,
Hsieh B. R.,
Gao Y.
Publication year - 1997
Publication title -
polymers for advanced technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.61
H-Index - 90
eISSN - 1099-1581
pISSN - 1042-7147
DOI - 10.1002/(sici)1099-1581(199707)8:7<408::aid-pat664>3.0.co;2-6
Subject(s) - x ray photoelectron spectroscopy , band bending , materials science , sulfur , phenylene , metal , poly(p phenylene vinylene) , work function , oxygen , impurity , photoemission spectroscopy , ether , schottky barrier , analytical chemistry (journal) , chemistry , nanotechnology , organic chemistry , chemical engineering , polymer , optoelectronics , engineering , composite material , electroluminescence , layer (electronics) , diode , metallurgy
We used X‐ray photoemission spectroscopy (XPS) to investigate the surface species of poly(p‐phenylene vinylene) (PPV) and its interface formation with Ca and Al. PPV surfaces compositions varied with sample preparation. For relatively ""clean'' surfaces with 4–5% O, analysis of the O 1s peak revealed four types of oxygen species, namely carbonyl (C=O), hydroxyl (C–OH), ether (C–O–C) and the carboxylic groups (HO–C=O). The oxygen groups, excluding ether, reacted with Al or Ca to form the corresponding metal oxides. Chemical interactions between the metals and the phenylene and vinylene units to yield new species were not detected. For sulfur‐free surfaces, a C 1s peak shift of +0.5 eV followed the deposition of 15–30 Å of Ca on PPV. For sulfur‐containing surfaces, the C 1s peak shift was −0.5 eV. We attribute this difference to the interaction of metal atoms with the sulfur impurities. For Al/PPV, a C 1s peak shift occurred at <2 Å of Al deposition and reached a constant value of about +0.4 eV after ⪅8 Å of Al. Again, the direction of the peak shift depended on the presence of sulfur impurities. We attribute the C 1s peak shifts to surface band bending and to Schottky barrier formation. Since surface oxidation of PPV can inhibit band‐bending, our overall results suggest that the barrier height at the metal/PPV interface is highly sensitive to the surface preparation and relatively insensitive to the work function of the metals. The shift seen by XPS in the C 1s core level spectra of PPV points clearly to charge transfer and Schottky barrier formation at the interface as a result of metal deposition. These results imply that the metal/polymer interface is not rigid and that triangular barrier tunneling fails to take into account the effect of barrier formation. We propose a band‐bending modified tunneling (BBMT) model to explain charge transfer at the Ca/polymer interface. © 1997 John Wiley & Sons, Ltd.