Adsorption and Reaction of NO on Ni(100)

The adsorption, desorption and decomposition of NO on Ni (100) was studied with XPS, UPS, XAES, ΔΦ, temperature programmed thermal desorption (TPD) and LEED in the temperature range 80 to 1300 K. NO adsorbs molecularly on Ni (100) at low temperatures; dissociation occurs above 200 K. Up to ≈ 1/4 saturation coverage, only N2 desorbs in a second order peak around 1100 K. At saturation three NO desorption states at 350, 420 and 1200 K and two N2 peaks at 660 and 1020 K are observed for a heating rate ß of 5 K/s. Activation energies for desorption are obtained by TPD with variable ß. Coadsorption experiments show that the NO-TPD peak at 1200 K is due to recombination of N and O on the surface. The relative areas of some TPD maxima depend strongly on coadsorbed O-, C- and N-impurities. At 100 K, ΔΦ increases up to a maximum of 1.1 eV at 3/4 saturation coverage and drops to 1.0 eV at saturation. Complex LEED patterns are observed for saturated layers adsorbed below 200 K which change during heating. The nature of the observed binding and desorption states is discussed.