Chemisorption of nitrogen on Cr(110)

The chemisorbed state of nitrogen on a Cr(110) surface at 300 K has been investigated by means of electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and work function change measurement (Δφ). The dissociative state is suggested by our observations that the EELS spectrum and the N(KLL) Auger line shape of the Cr(110) surface after N 2 adsorption at 300 K are practically the same as those of the nitride-covered surface formed by NH 3 exposure at 800 K. From the Auger uptake curve, the initial sticking probability and the saturation coverage at 500 L N 2 are estimated respectively to be 0.09 and 0.36. Both the Auger uptake and the work function decrease (saturation value: -0.27 eV) show an abrupt change at about 10 L. The clean-surface EELS peaks due to the interband transitions in the low energy range of 2–20 eV have merely decreased and the high-energy side tailing of the loss peaks at 5.0 and 9.0 eV is observed after N 2 adsorption. Although the nitrogen-induced EELS peaks are not distinctly resolved in the low-energy range at less than 30 eV, the shift of the loss peak at 41.5 eV due to the Cr 3p core-level excitation is clearly observed at about 10 L in accordance with the AES and Δφ results. The above results strongly indicate the onset of transformation of the chemisorbed phase to the surface nitride phase on Cr(110) surface at about 10 L N 2 exposure even at 300 K.