Development of spin polarized metastable atom source and application of surface magnetic analysis

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Electronic properties of potassium-doped dibenzopentacene thin films were studied by electron spectroscopy method using herium metastable atom as a probe. The spectra for KxDBP (0 < x < 3.5) films show three types of gap state in the HOMO-LUMO gap of pristine DBP. The threshold of electron emission for K1DBP is located ~0.1 eV below the Fermi level with no metallic feature, suggesting that K1DBP is a Mott-Hubbard insulator. At the formation of K2DBP, the film has a wide-gap insulator. Upon further deposition of K, the new gap state appears near Fermi level and is attributed to partial electron filling in the LUMO+1~LUMO+3 states, however, the leading edge of the gap state is located ~0.1 eV below Fermi level without a metallic feature. Therefore, the heavily doped species transfers to a Mott-Hubbard insulator again. The gap state plays a key role in superconductivity of K3.5DBP at low temperature.