Determination of correct composition in nickel–phosphorus films by XPS angle resolved technique

Surface sputtering is a commonly used technique for surface analysis. The standard method of Ar+ sputtering was found to produce surface changes or damages. In this work, nickel–phosphorus films are characterized by X-ray photoelectron spectroscopy (XPS) angle resolved technique before and after sputtering. A method is presented to determine the correct atomic ratio between Ni and P in the surface layers, taking into account that nickel atoms are mainly displaced toward inner layers, as a consequence of 4–5 at.% argon ion implantation within top 1.5–3.7 nm from the surface. The experimental argon implantation and nickel displacement ranges match with Lindhard–Scharff model. Metallic nickel formation in the first layer is detected after sputtering by X-ray diffractometry at low glancing angle. No detectable difference was found between the binding energy of nickel in the metallic state and in the Ni–P coating, showing a similar chemical state for nickel in both conditions.