STM, LEED and AES studies on the oxidation of a CrN overlayer on Fe 0.8Cr 0.2(100)

Abstract

A combination of Scanning Tunneling Microscopy (STM), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED) was used to study the CrN surface phase grown on a Fe 0.8Cr 0.2(100) substrate. The co-segregation of Cr and N was achieved by annealing the Fe 0.8Cr 0.2(100) crystal to 833 K. LEED data of the annealed surface showed a sharp (1 × 1) pattern corresponding to the segregated CrN phase. STM images showed that the CrN overlayer is rough and inhomogeneous, exhibiting many deviations from ideal regularity. Steps were observed with terrace widths ranging from 5 to 65 nm. The step heights are in the range 0.2–3.5 nm. Most of the steps are oriented preferentially in the 〈100〉 direction. Oxidation of the surface results in disordering of the CrN layer (1 × 1) LEED pattern. STM measurements revealed oxide island formation at saturation coverage. Our Auger data suggest that a Cr oxide overlayer forms over the surface nitrogen. Auger spectra indicated that exposure to O 2 results only in the oxidation of Cr while the underlying Fe is still metallic. Tunneling current-voltage measurements and Auger spectra at different O coverages can be correlated with the surface oxidation behavior of the CrN overlayer. Comparison of the CrN(1 × 1) layer with a N-depleted surface indicates that surface N retards oxidation at 300 K.