NOBLE-GAS-LIKE MECHANISM OF LOCALIZED FIELD-IONIZATION OF NITROGEN ASDETECTED BY FIELD-ION APPEARANCE ENERGY SPECTROSCOPY

A local (probe-hole) mass-to-charge resolved retarding potential analy sis of N-2(+) emitted from a few surface sites of the apex plane of a [111]-oriented W tip is carried out and corresponding field ion appear ance energies are obtained. A comparison of the results of N-2(+)/W(11 1) field ion appearance energy spectroscopy with independently obtaine d field-free nitrogen adsorption data reveals a noble-gas-like mechani sm for the localized field ionization of N-2, supplied as imaging gas in the field ion microscope. The differences in the physical nature of the field-dependent terms of the appearance energy of N-2(+) and COfield ions are discussed in relation to the peculiarities of the high- field modified interaction of nitrogen and carbon monoxide with the tu ngsten surface.