The field desorption of Ba has been studied over a range of fields and coverages in an attempt to determine the mechanism of desorption and the charge of the desorbing species. It was found that adsorption seems to be polar but not ionic and that desorption of Ba++occurs under our conditions. If this interpretation is correct agr;cong;60 Aring;3for the polarizability of adsorbed Ba results, close to the value for the free atom. The accessible fieldhyphen;temperature range is restricted by the onset of fieldhyphen;dependent surface diffusion, which was also investigated. It was found that positive fields have more effect on the activation energyEdand prehyphen;exponential term of the diffusion coefficient than negative ones. While a frac12; agr;F2dependence ofEdis compatible with the limited data obtained for negative fields, no simple behavior was found for positive ones,Edgoing through a minimum of 0, accompanied by a drastic reduction in prehyphen;exponential term. A tentative explanation in terms of a compensation effect is advanced.Values for the zero field heat of adsorption were obtained over a wide coverage interval and agree well with those of Moore and Allison where overlap occurs.
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