Oxygen effect on the interfacial electronic structure of C60 film studied by ultraviolet photoelectron spectroscopy

Oxygen effect on the electronic structure of the interface between C60 and highly-oriented pyrolytic graphite was investigated by ultraviolet photoelectron spectroscopy (UPS). The film deposited in ultrahigh vacuum showed downward band bending characteristic of n-type semiconductor, possibly caused by residual impurities working as unintentional n-type dopants. In contrast, the film deposited in O2 atmosphere (1.3 × 10−2 Pa) did not show such band bending. Possible origins of this difference are discussed in terms of (i) deactivation of an unidentified dopant, (ii) compensation by O2 working as an acceptor, and (iii) O2-related carrier-traps such as O2 itself, O 2 δ - C 60 δ + and/or C60Ox.