A study of the interface formation between gold and a thin conjugated oligomer film

The interface formation between Au and a five-ring n-octyloxy substituted phenylenevinylene (Ooct-OPV5) oligomer film was studied by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS), in ultrahigh vacuum. When the oligomer was stepwise deposited on a clean Au polycrystalline foil, an abrupt interface was formed. A high binding energy component present in the oligomer related XPS C1s peak up to the completion of the first monolayer, revealed the existence of an interfacial state. The C1s peak exhibited a total upward BE shift of ∼0.5 eV, related to the band bending in the oligomer film. When Au was stepwise deposited on a ∼5 nm thick oligomer layer, UPS and angle resolved XPS revealed extended diffusion of the Au atoms in the oligomer. The C1s and Au4f peaks exhibited ∼0.5 and ∼0.65 eV downward BE shifts respectively. These shifts are a combination of initial and final state effects in gold and charge transfer between the two materials in contact.