Field adsorption of inert gas atoms on the tungsten surface: A pulsed-laser atom-probe study

On a solid surface, inert gas atoms can be field adsorbed to the surface under the influence of a strong electric field. The probability of field adsorption was measured as a function of temperature for He, Ne, and Ar on the W(112) surface. Although it was assumed that gas atoms field adsorb only on top of surface atoms, experimental evidence indicates that secondary sites also exist, such as on bridge sites, between surface atoms, or second layer adsorption sites. A simplified calculation of the binding energy assumes an isolated dipole pair model and significantly overestimates the binding energy at 0.20, 0.19, and 0.24 eV for He, Ne, and Ar at a field of 4.5, 3.9, and 2.5 V/A, respectively. The measured values were 0.17, 0.14, and 0.12 eV. Including a correction for the depolarizing field caused by the layer of polarized adatoms gives a reasonable agreement with the experimental values at 0.18, 0.16, and 0.13 eV