Time of Flight Analysis of Field-Ionized He in Mixtures with Ne or Ar

Abstract

An enhancement of current of field-ionized He from a W⟨111⟩ gas field ion emitter in mixtures with Ne or Ar and its origin were investigated by a field ion microscope equipped with a time of flight (ToF) spectrometer. He ion current was increased up to three times by He-Ne mixture and two times by He-Ar mixture, respectively. Mass to charge ratio spectra show that only He atoms were field-ionized at a field of operating condition of a He gas field ion source. In both gas mixture conditions, a peak of singly charged He in ToF spectra shifted after the mixture of He and Ne or Ar, which corresponds to that He was field-ionized at lower potential energy. These observations indicate that He atoms field-adsorbed on a tungsten surface are exchanged for Ne or Ar atoms and the exchange of species of field-adsorbed atom is also related to the enhancement of He ion current. [DOI: 10.1380/ejssnt.2016.23]