AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThP

Paper AS-ThP1
Mass Spectral Frequency Plots: A New Tool For Static SIMS Data Interpretation

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Aspects of Applied Surface Science Poster Session
Presenter: A.M. Spool, IBM Corporation
Correspondent: Click to Email

The experienced Static SIMS Analyst will examine common peak mass differences in addition to common peak positions in attempting to interpret a spectrum of a new or unknown sample. Mass differences of 44 amu, for example, suggest polymers with an ethylene oxide monomer, common to many surfactants. Many species with biological origins will display peaks differing by 2 methylene groups (28 amu). Fluorinated polymers will often have peaks with mass differences of 50 amu corresponding to a perfluorinated methylene. Spectra of many polymers will have common peak differences that correspond to the mass of their monomers. In this paper I propose a simple algorithm that converts spectra with unit mass resolution to a plot of the "frequency" of peaks in the mass spectrum. The resulting "pseudo-power spectra" or "mass spectral frequency plots" are more indicative of the type of species on the sample than the exact identity of these species. The algorithm proposed simply involves multiplying the intensity of the peak at each mass by the peak intensity at every other mass, and adding each result to the bin corresponding to the difference between the masses. The intensities of the resulting peaks at each "delta" are a function of the number of peaks with those mass differences, and the intensities of the original peaks. Examples of these plots will be shown and their utility demonstrated.