Page 218 - Inorganic Mass Spectrometry - Fundamentals and Applications

Secondary Ion ¸ ass ~~ectro~et~ 203

<loL3 primary ions/cm2 (the static SIMS limit) striking the surface. This require-
ment for limited bombardment of the surface puts a premium on efficient use of
the available ions. The availability of high mass resolution, high transmission, and
of
a
high useful yields (with the advent new generation of time-of-flight SIMS mass
spectrometers in the late 1980s) provided a strong boost for SSIMS applications,
a
Since the late 1980s there has been blossoming of SSIMS, primarily in the area
of organic and polymer applications. Of prime importance in SSIMS is determin-
ing the relationship between the sputtered species and the molecules on the sur-
face. Rvo libraries of SSIMS spectra are available to help the analyst, the Munster
High Muss ~esolution Static SI~S Library [1 121 and The Static SIMS Library
[l 131. Also critically important to SSIMS is ultrahigh vacuum in the 10-lo-torr
range or lower in the sample chamber to prevent cont~nation of the surface.
A classic example of SSIMS is a study of the initial stages of oxidation of
chromium [l 141. Figure 4.35 shows the changes in the Cr0,-, Cr0,-, and CrO+
0 to 1000 langmuir (L). After -SO L
ions as oxygen exposure was increased from
of exposure the Cr0,- and Cr0,- species begin to increase. At about 300 L, CrO+

~ x y ~ ~ n(Lan~muir)
dose
ur Static secondary ion mass spectrometry (SIMS) study of the initial stages of
oxidation on chromium surface. (From Ref. 114.)