FIELD ADSORPTION AND DESORPTION OF HELIUM AND NEON

Pulsing the atom-probe FIM in the presence of the imaging gases He or Ne reveals the adsorption of these noble gases on the surface of tips of W, Fe, Ir and Rh at temperatures as high as 78°K. A minimum field is necessary for the adsorption; for He 2.0 V A ̊ is required at 21 °K and 3.3 V A ̊ at 78°K, while with Ne, adsorption at 78 °K occurs between 2.3 and 5.0 V A ̊ only. Field desorption of the noble gas ions appears to require the simultaneous field evaporation of the tip metal atoms, which sometimes form various metal-noble gas molecular ions. The binding of the noble gas atoms is almost entirely due to the polarization energy 1 2αF2. Field desorption appears possible only through the catalytic action of multiply charged metal ions. These effects suggests some reservations in the interpretation of all field evaporation data previously obtained in the presence of the image gas. © 1969.