Noble-gas-like mechanism of localized field ionization of nitrogen as detected by field ion appearance energy spectroscopy

A local (probe-hole) mass-to-charge resolved retarding potential analysis of N2+ emitted from a few surface sites of the apex plane of a [111]-oriented W tip is carried out and corresponding field ion appearance energies are obtained. A comparison of the results of N2+W(111) field ion appearance energy spectroscopy with independently obtained field-free nitrogen adsorption data reveals a noble-gas-like mechanism for the localized field ionization of N2, 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 N2+ and CO+ field ions are discussed in relation to the peculiarities of the high-field modified interaction of nitrogen and carbon monoxide with the tungsten surface.