Abstract
The influence of the primary ion current density on the secondary ion emission from clean surfaces has been investigated. The experiments were carried out in a quadrupole equipped mass spectrometer using 10–12 keV argon primary ions. A focussing device in the vicinity of the target allowed the current densities to be varied between some 10 μA/cm 2 and 10 mA/cm 2 at beam currents between 1 and 5 μA. Energy spectra of secondary ions could be obtained by use of a suitable energy analyser preceding the quadrupole mass filter. Due to focussing the secondary ion intensities increased markedly for a variety of metal targets. The effects were most pronounced for noble metals, in particular for gold where the yield increased by up to a factor of 20. The enhancement is attributed to ionization taking place in vacuum at large distances from the target surface. Several ionization processes are considered which may account quantitatively for the magnitude of the effects observed.
Published Version
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