Page 196 - Inorganic Mass Spectrometry - Fundamentals and Applications

I82 Cristy

I6O- PRI~ARY ION BEA

Profile of sodium in SiO, acquired with 160+ primary beam shows effect of
charge-driven diffusion. Profile acquired with I6O" primary beam shows noma1 profile.
(From Ref. 80.)

creases with increasing availability of free electrons. Therefore, targets with low
work function surfaces, such as gold, have very low positive secondary ion yields.
The work function of metal surfaces can be increased and, thus, the positive sec-
ondary ion yields improved the che~so~tion reactive electronegative gases
of
by
or by the use of a reactive gas ion beam to form strongly bonded compounds in the
target. Conversely, negative secondary ion yields are enhanced by increasing the
availability of free electrons, by using a very electropositive bombard in^ ion such
as CS+. As can be observed in Figs. 4.25 and 4.26, high-sensitivity analyses for a