STM, LEED AND AES STUDIES ON THE OXIDATION OF A CRN OVERLAYER ON FE0.8CR0.2(100)

A combination of Scanning Tunneling Microscopy (STM), Auger Electron S pectroscopy (AES) and Low Energy Electron Diffraction (LEED) was used to study the CrN surface phase grown on a Fe0.8Cr0.2(100) substrate. T he co-segregation of Cr and N was achieved by annealing the Fe0.8Cr0.2 (100) crystal to 833 K. LEED data of the annealed surface showed a sha rp (1 x 1) pattern corresponding to the segregated CrN phase. STM imag es showed that the CrN overlayer is rough and inhomogeneous, exhibitin g many deviations from ideal regularity. Steps were observed with terr ace 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 x 1) LEED pattern. STM measurements revealed oxide island fo rmation at saturation coverage. Our Auger data suggest that a Cr oxide overlayer forms over the surface nitrogen. Auger spectra indicated th at exposure to O-2 results only in the oxidation of Cr while the under lying Fe is still metallic. Tunneling current-voltage measurements and Auger spectra at different O coverages can be correlated with the sur face oxidation behavior of the CrN overlayer. Comparison of the CrN(1 x 1) layer with a N-depleted surface indicates that surface N retards oxidation at 300 K.