Electron stimulated desorption of Xe, Kr, and Ar

Abstract Electron stimulated desorption cross sections have been measured for Xe, Kr, and Ar overlayers on the Ag(111) surface. The Xe cross section is less than 10 −4 A 2 ; the Kr cross section is strongly temperature dependent, rising from 0.1 A 2 at 10 K to 0.18 A 2 at 50 K; the Ar cross section is 4 A 2 and temperature independent. These results are rationalized using a model of the stimulated desorption similar to that proposed by Antoniewicz [Phys. Rev. B21 (1980) 3811], in which an atom is ionized by the incident beam, accelerates towards its image and is neutralized, desorbing only if the kinetic energy gained is greater than the neutral atom binding energy at the neutralization position. Fitting these data requires an exceedingly rapid dependence of the neutralization on distance for these slow ions. Rather than the effect of the mass on the ion velocity, the most important effect in determining the diverse behavior of the different gases is that the equilibrium position for the heavier gases is farther up the overlap repulsive potential and so in a region of more rapid neutralization. The model identifies several contributions to the isotope effect, predicting it to be temperature dependent. The results are extremely sensitive to the anharmonicity of the holding potential.