Cluster Primary Ion Sputtering: Secondary Ion Intensities in Static SIMS of Organic Materials

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Positive secondary ion spectra from Irganox 1010, sputtered by Ar+, Bi+, and primary ions at 25 keV impact energy, are analysed in detail. Irganox 1010 consists of a central carbon atom with 4 identical side chains or arms, each of C18H27O3. First, it is shown that the previously established relation, in which the secondary ion yield of the molecular species is proportional to the square of the sputtering yield, is accurately validated but, this time, for the positive, protonated molecular secondary ion instead of the previous negative deprotonated molecular secondary ion. Next, it is shown that the spectral ratios for Bi+/Ar+, and for 389 mass channels, are comprised of the product of two basic spectra called and raised to powers as defined in the text. These descriptions are valid to a remarkably low relative standard deviation of 2.3% over the 389 mass channels. The above squared dependence is inherent in both and so that it is likely that all similar primary ion sources will exhibit the same squared dependence on the sputtering yield as found earlier for the (M-H)- yields. The power of 2 is reduced for lower mass secondary ion fragments, falling to ~1.5 for fragments that have 3 or 4 of the 4 arms of the molecule intact and to unity for those fragments that are parts of an arm. For the G-SIMS of peaks with m/z £ 300 u it is recommended to use Bi+ and Mn+ (or Ar+) and not the cluster sources but for higher mass peaks if insufficient intensity has been obtained, or should be used with either Bi+ or Mn+ (or Ar+). The benefit at high mass results from the enhanced sputtering available with or , and often required for adequate data in the high secondary ion mass regime.