A new and simple method to determine the temperature coefficient of effective work function for thermal positive ion production on a clean polycrystalline metal surface

Abstract

The total emission current of Li + ions produced from LiI molecules incident upon a polycrystalline rhenium filament heated to a constant temperature ( T) was measured as a function of the time ( t) immediately after the filament was flashed at ∼ 2200 K for ∼ 3 min. This measurement was made at various temperatures, and each emission curve including a small peak at t ≲ 1 s was analyzed by our original theory on dissociative thermal ionization. Even under an easily attained residual-gas pressure (∼ 2×10 −7 torr), this new and simple method made it possible to determine the temperature coefficient of the effective work function (φ 0 +) for thermal positive ionization on a clean surface of the filament, yielding the following equation in the range of ∼ 1150–2150 K. φ 0 + = (5.247±0.008)+(1.47±0.05)×10 −4× T where φ 0 + and T are expressed in eV and K, respectively.