TDS study of the bonding of CO and NO to vacuum-cleaved NiO(100)

Using thermal desorption spectroscopy (TDS) we have determined the adsorption enthalpies of NO and CO on a NiO(100) surface obtained by cleavage of a NiO single crystal rod under ultra-high vacuum (UHV) conditions. The TDS data have been evaluated using the leading edge method and complete analysis, yielding values of 0.30+/-0.04 and 0.57 +/-0.04 eV for the heats of adsorption of CO and NO, respectively, in the low coverage regime. These values decrease with increasing coverage down to the respective multilayer values. The results obtained experimentally are different from the theoretical ones, in that the experimental values are systematically larger. This is possibly due to the influence of the Ni3d electrons as concluded from a comparison with TDS data for CO on vacuum-cleaved MgO(100). The adsorbate bonding energies obtained for vacuum-cleaved NiO(100) are in good agreement with values for thin NiO(100) films deduced from thermal-desorption studies and infrared investigations. (C) 1999 Elsevier Science B.V. All rights reserved.