Surface Ionization of Niobium

Abstract

By measuring the temperature dependence of Nb+ emission from a niobiumsurface heated between 1990° and 2175°K; a value of 10.39±0.15 eV was obtained for the heat of ion vaporization. The work function for the niobiumsurface was found to be 3.90±0.05 eV in the 1850°‐to‐2025°K temperature range. The method used for this determination consisted of a mass‐spectrometric measurement of the ratio of positive to negative ions formed when a constant‐intensity beam of alkali halide molecules impinged upon the niobiumsurface. These quantities, together with the ionization potential of niobium are sufficient to derive a value of 7.45 eV for the heat of niobium sublimation at absolute zero. This is in excellent agreement with previous direct determinations of this quantity.