S. Toyoshima, T. Sakurai, T. Taima
Feb 15, 2008
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12
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Journal
Japanese Journal of Applied Physics
Abstract
The electronic structure at the interface between bathocuproine (BCP) and calcium (Ca) was studied by ultraviolet photoemission spectroscopy (UPS) using two kinds of thin-films: Ca and BCP codeposited film, and BCP deposited on Ca. New peaks caused by the interaction of Ca with BCP were observed near the Fermi level. The energy position of the highest occupied molecular orbital (HOMO) of BCP measured from the Fermi level did not change with the thickness of BCP on Ca and the composition ratio of BCP to Ca. The new peaks related to the interface states shifted with the thickness of BCP on Ca and the composition ratio of BCP to Ca. It is suggested that the interface states are generated by the interaction of the Fermi level of Ca with the lowest unoccupied molecular orbital rather than the HOMO.