Adsorption and Reaction of NO on Ni(100)

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Abstract
The adsorption, desorption and decom position 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 β of 5 K/s. Activation energies for desorption are obtained by TPD with variable β. 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 o f the observed binding and desorption states is discussed.

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