ENERGY-RESOLVED ATOM PROBE SPECTROSCOPY OF FIELD-ADSORPTION PHENOMENA

The effect of an electric field on the interaction of He and Ne with W tips in an FIM is investigated using a retarding potential analyzer combined with a magnetic sector atom probe. Appearance-energy analysis and measurements of surface-temperature dependencies, especially of electron-stimulated field desorbed Hen+ and Nen+-yields, enable the determination of binding distances, vibration frequencies and desorption energies as a function of electric field strength. The experimental data are compared with results of a recent quantum theoretical calculation that suggests formation of a weak chemisorption bond for field adsorbed He. The He-W and the Ne-W bonds are considerably strengthened within the experimentally accessible field strength range of 3-5 V/Å. The image-plane position for Hen+/W is estimated from a comparison of calculated and measured binding-distances