Chemical bonding of nitrogen in low-energy implanted chromium

Chromium nitride films have been grown by nitrogen implantation of metallic chromium at room temperature in the energy range of 0.25–5 keV varying the ion dose, the ion beam energy and the angle between the ion beam and the normal to the surface. X-ray photoelectron spectroscopy (XPS) and Factor Analysis (FA) have been used to characterize in situ the chemical composition of the films. The number and spectral shape of the different Cr–N phases formed during nitrogen implantation, as well as their concentrations, have been obtained by means of FA, involving principal component analysis and target testing transformation, of the Cr 2p and N 1s XPS bands. FA results show that the composition of the chromium nitride films depends on the ion dose, on the ion energy and on the angle between the ion beam and the normal to the surface. For all ion beam energies two chromium nitride phases are formed, that is, Cr2N and CrN, however, for ion beam energies ≤ 0.5 k eV and normal incidence, the films are only composed of CrN, that is, the phase with the highest nitrogen content. For those experimental conditions, comparison of the experimental nitrogen concentration obtained by FA with that obtained from TRIDYN simulations suggests that in addition to nitrogen implantation and atomic mixing, other mechanisms like ion beam enhanced diffusion or the chemical reactivity of the Cr substrate towards nitrogen should be taken into account at low ion energies.