Singly charged tungsten and tantalum ions observed during high-temperature field evaporation

High-temperature field evaporation of tungsten and tantalum emitters in the temperature range from room temperature to 2500 K is studied using a static magnetic mass spectrometer equipped with a field source of ions. At room temperature, triply charged W³⁺ and Ta³⁺ ions alone are observed in the mass spectra. However, as the emitter temperature grows, the charge of the ions decreases. At T ≈ 1000 K, doubly charged W²⁺ and Ta²⁺ ions dominate in the spectra, and singly charged W⁺ and Ta⁺ ions appear in the temperature range 1900 < T < 2500 K. The evaporation rate of the singly charged ions is one to two orders of magnitude lower than the evaporation rate of the doubly charged particles. The energy parameters of field evaporation for differently charged tungsten ions are found.