Electronic structure and mechanical properties of hard coatings from the chromium–tungsten nitride system

Abstract
Cr1−xWxNy films were deposited on silicon by rf reactive magnetron sputtering. The phase and texture were determined by x-ray diffraction analysis. All the films crystallize in the fcc phase. Scanning tunneling microscopy revealed a finely grained surface morphology. The grain size decreases with increasing tungsten content in the films. Quantitative values can be assigned to morphology differences through the measurement of the optical reflectivity. Hardness values obtained by nanoindentation, and the packing density significantly increase upon addition of a small percentage of W to CrN. The electronic structure was analyzed using x-ray photoelectron spectroscopy. As deduced from core level binding energy values (chemical shifts), the W2N and Cr1−xWxN films are more covalent than binary CrN. The higher hardness values in W2N and Cr1−xWxN compounds compared to that of CrN are related to their prominent covalent bonding character between the metal and nitrogen ions.