The energy distributions of the ions produced in a reversed hollow cathode glow discharge ion source were studied using a Cameca IMS 3f mass spectrometer. Aluminum cathodes containing various impurities at concentrations of a few hundred parts per million (ppm) were used. Two prominent peaks were found in the energy distributions, corresponding to ions with high kinetic energies (formed in the negative glow region of the discharge) and ions with low kinetic energies (formed near the cathode potential at or near the extraction aperture in the base of the hollow cathode). For Al+ ions, the high-energy peak is more intense than the low-energy peak, while for Ar+ ions the high-energy peak is much weaker than the low-energy peak due to efficient resonant charge exchange in the cathode dark space. Similar results, showing a weak high-energy peak and an intense low-energy peak, were obtained for cluster ions. These ions are collisionally dissociated in the cathode dark space, and only those ions formed near the cathode exit aperture have a significant probability of escape. Thus, the interfering signals from cluster ions and the discharge gas may be significantly reduced by adjusting the mass spectrometer to sample only the high-energy ions emanating from the negative glow.
ASJC Scopus subject areas
- Analytical Chemistry