The super-efficient diffusion of Cs into (10•0)Re which was covered with a 2-dimensional graphite film was studied. If a flux of Cs atoms with a density of 1013/cm2s was incident on uncoated Re at 1800K, the efficiency of their diffusion into the bulk was of the order of 10-10. However, if Cs atoms were deposited at 1800K onto a Re surface that was covered by a graphite film, the efficiency of their diffusion into the bulk increased sharply to values which were of the order of 0.1 to 0.5. The mechanism of super-efficient diffusion involved the efficient migration of Cs atoms from the surface under graphite islands in the adlayer on the metal, and was based essentially on their extremely long lifetime under the islands; from where they diffused into the bulk of the metal. Ribbons of Re in which the near-surface region was saturated by Cs via super-efficient diffusion could serve as an efficient source of Cs. Such a source was capable of emitting fluxes with densities of between 109 and 3 x 1012/cm2s when the ribbon temperature was varied between 1800 and 2200K. At a given ribbon temperature, the Cs flux remained constant for many hours. After exposure to the atmosphere, Cs-saturated Re ribbon continued to emit Cs under ultra-high vacuum conditions. The activation energies for Cs diffusion into (5.65eV) and out of (5.85eV) Re were determined.

A.J.Tontegode, F.K.Yusifov: Applied Surface Science, 1995, 90[2], 185-90