Thermal Desorption of Sr from W

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Abstract
A study of the kinetics of the thermal desorption of Sr from W has been performed in which the field electron microscope was used to identify the state of adsorbate—substrate system. The activation energy for the thermal desorption of Sr from W falls from 4.21±0.22 eV/atom at zero Sr coverage to 1.78±0.13 eV/atom at ``monolayer'' coverage. This latter value approaches the heat of sublimation of bulk Sr (1.69 eV/atom). The desorption energies found using field-emission techniques deviate markedly from the extrapolated thermionic results of Moore and Allison near θ=0 and for θ>0.5. A linear relationship was found to exist between the activation energy for desorption and the logarithm of the pre-exponential factor in the rate equation κ(kT/h) exp(ΔS‡/R).

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