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

Abstract

Positive secondary ion spectra from Irganox 1010, sputtered by Ar+, Bi+, Bi3 +, and Bi5 + primary ions at 25 keV impact energy, are analyzed 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, for the first time, that the spectral ratios for Bi+ primary ions to that for Ar+ primary ions, for Bi3 + to Ar+ and Bi5 + to Ar+, for 389 mass channels, are comprised of the product of two basic spectra called H Irg * and L Irg * 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 H Irg * and L Irg * 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 largely intact and to unity for those fragments that are parts of an arm. This work also shows that, for the G-SIMS of peaks with m/z ≤ 300 u it is recommended to use Bi+ and Mn+ (or Ar+) whereas, for higher mass peaks, cluster primary ions, such as Bi3 + or Bi5 +, should be used with either Bi+ or Mn+ (or Ar+) to obtain the best signal quality.

Systematic Temperature Effects in the Argon Cluster Ion Sputter Depth Profiling of Organic Materials Using Secondary Ion Mass Spectrometry

“…It is important to evaluate any compositional or other changes with increasing temperature. NPB and Irganox 1010 SIMS spectra may be found elsewhere and so are not given here [43]. The spectra for all temperatures are basically very similar and show no signs of decomposition or other significant changes except as discussed below.…”

Organic secondary ion mass spectrometry: Signal enhancement by water vapor injection

“…It was found to enhance the yields of characteristic ions by one or two orders of magnitude depending on the sample, and even more in some instances [8 -10]. With the advent of polyatomic projectiles, such as SF 5 ϩ , C 60 ϩ , Bi n ϩ , and Au n ϩ , huge molecular ion yield enhancements have been measured (up to 1000-fold increases in signal compared with Ga ϩ atomic projectiles), leading to a revolution of the field of organic SIMS characterization [11][12][13][14][15]. With the additional molecular depth profiling capabilities of SF 5 ϩ and C 60 ϩ cluster beams, one can now hope to relate the performance characteristics of organic devices to their surface molecular composition in a much more quantitative way.…”

Relationships between cluster secondary ion mass intensities generated by different cluster primary ions

“…Elsewhere [12], we show that for Bi n ϩ primary ions, the spectra, I͑Bi n ϩ ͒, for the cluster sputtering of the organic molecule, Irganox 1010, in the static SIMS limit [36] may be predicted very accurately from the spectrum for argon, I(Ar ϩ ), using the relation…”

“…Different spectrometer manufacturers fit different primary ion sources. It is important, therefore, if analysts are to make the best use of their instruments and of the published literature and data sources, that the relationships for the secondary ion spectra from different primary ion sources is characterized and understood.Elsewhere, we have studied the secondary ion mass spectrum from organic materials in detail for a number of primary ions and have proposed that the spectra are all related accurately to one another by three samplerelated component spectra with the observed spectrum being a product, not a sum, of those component spectra [12]. It is important to understand if this is a generic effect in SIMS or if it is limited, in some way, to organic materials.…”

“…Elsewhere, we have studied the secondary ion mass spectrum from organic materials in detail for a number of primary ions and have proposed that the spectra are all related accurately to one another by three samplerelated component spectra with the observed spectrum being a product, not a sum, of those component spectra [12]. It is important to understand if this is a generic effect in SIMS or if it is limited, in some way, to organic materials.…”