The interface formation between a conjugated oligomer (Ooct-OPV5, [(2,5-Bis(4-styryl) styryl)1,4-dioctyloxybenzene]) and ultrathin (6 and 15 Angstrom thick) SiOx (x less than or equal to 2) layers on n-doped Si(111), was studied by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). Ooct-OPV5 is a model oligomer for PPV [poly(p-phenylenevinylene)], a polymer that has been used in organic light emitting diodes. An similar to 8 nm thick oligomer film was grown stepwise on the sputter-cleaned SiOx substrates under ultrahigh vacuum conditions. XPS and UPS results show the layered growth of the oligomer on both substrates. Upon deposition of the oligomer on the similar to6 Angstrom thick SiOx film, a dipole of similar to0.20 eV is formed at the Ooct-OPV5/SiOx, interface. When the oligomer is deposited on the similar to15 Angstrom thick SiOx film an interfacial state is observed, which is related to a similar to0.45 eV dipole formed at this interface. The energy level diagram of the Ooct-OPV5/SiOx/Si(111) interfaces is deduced in both cases from the combination of XPS and UPS results. (C) 2003 Elsevier B.V. All rights reserved.