XPS and SERS evidence for iron nitride species responsible for the strong adhesion of polypyrrole to iron or steel treated with nitric acid

The reason for the strong adhesion of polypyrrole (PPy) films to iron and mild steel surfaces pretreated with dilute nitric acid (HNO3) has been investigated by XPS and SERS techniques. It is shown that iron nitride (Fe≡N) species, arising from the reaction of HNO3 with the metal, are strongly grafted to the surface. These species could be responsible for the adhesion of PPy films to iron surfaces.