Alkali overlayers on aluminum, alumina, and aluminum carbide

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Abstract
Adsorption data for potassium and sodium atoms on the surfaces of aluminum metal, aluminum oxide, and aluminum carbide are presented. Low coverage adsorption of K(Na) on Al(100) is characterized by a 4.6(3.2) D surface dipole and desorption around 620(590) K. Increasing the alkali coverage lowers the desorption temperature as well as the effective surface dipole per alkali atom. Clustering on aluminum metal is activated by annealing to around room temperature. The adsorption of K and Na monomers on dehydrogenated Al2O3 is characterized by desorption around 350 K and, for sodium, by cluster formation even at submonolayer coverage. Finally, potassium but not sodium atoms bind strongly to Al4C3 (Id>700 K). This explains a previous observation of potassium at a promoted aluminum surface after exposure to carbon monoxide and annealing to 700 K.1,2

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