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

Using thermal desorption spectroscopy (TDS) we have determined the adsorpti on 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 da ta 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 adsorp tion of CO and NO, respectively, in the low coverage regime. These values d ecrease 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 possib ly due to the influence of the Ni3d electrons as concluded from a compariso n with TDS data for CO on vacuum-cleaved MgO(100). The adsorbate bonding en ergies obtained for vacuum-cleaved NiO(100) are in good agreement with valu es for thin NiO(100) films deduced from thermal-desorption studies and infr ared investigations. (C) 1999 Elsevier Science B.V. All rights reserved.