Adsorption of Pb on NiAl(110): energetics and structure

The adsorption of Pb onto a NiAl(I 10) single crystal surface at 300 K has been studied by Auger electron spectroscopy (AES), Low energy electron diffraction (LEED), molecular beam/surface scattering and single crystal adsorption calorimetry (SCAQ. AES indicates a Stranski-Krastanov growth mode, i.e., Pb initially grows on NiAl(110) two-dimensionally until the-first layer completes at 0.89 ML, where a ((1)(3) (3)(0)) superstructure is observed by LEED, followed by 3D islanding. Measurements of the Pb gas that does not stick indicate that Pb sticks on NiAl(110) with an initial probability of 0.99. The initial heat of adsorption of Pb on NiAl(110) is 249 +/- 10 kJ/mol. Due to the repulsive interactions between Pb adatoms, the heat of adsorption decreases within the first layer to a value identical to the heat of sublimation of bulk Pb (195 kJ/mol), where it remains at higher coverages. This first application of adsorption calorimetry on such a thick sample (75 mum versus 0.2-8 mum previously) demonstrates that adsorption calorimetry can be extended to a wider range of surfaces, since this thickness can be achieved with nearly any single crystal material by simple mechanical thinning. (C) 2004 Elsevier B.V. All rights reserved.