We report a method for the unambiguous identification of molecules in biological and materials specimens at high practical lateral resolution using a new TOF-SIMS parallel imaging MS/MS spectrometer. The tandem mass spectrometry imaging reported here is based on the precise monoisotopic selection of precursor ions from a TOF-SIMS secondary ion stream followed by the parallel and synchronous collection of the product ion data. Thus, our new method enables simultaneous surface screening of a complex matrix chemistry with TOF-SIMS (MS(1)) imaging and targeted identification of matrix components with MS/MS (MS(2)) imaging. This approach takes optimal advantage of all ions produced from a multicomponent sample, compared to classical tandem mass spectrometric methods that discard all ions with the exception of specific ions of interest. We have applied this approach for molecular surface analysis and molecular identification on the nanometer scale. High abundance sensitivity is achieved at low primary ion dose density; therefore, one-of-a-kind samples may be relentlessly probed before ion-beam-induced molecular damage is observed.

a An Ar Gas Cluster Ion Beam (GCIB) has been shown to remove previous Ar + ion beam-induced surface damage to a bulk polyimide (PI) film. After removal of the damaged layer with a GCIB sputter source, XPS measurements show minor changes to the carbon, nitrogen and oxygen atomic concentrations relative to the original elemental bulk concentrations. The GCIB sputter depth profiles showed that there is a linear relationship between the Ar + ion beam voltage within the range from 0.5 to 4.0 keV and the dose of argon cluster ions required to remove the damaged layer. The rate of recovery of the original PI atomic composition as a function of GCIB sputtering is similar for carbon, nitrogen and oxygen, indicating that there was no preferential sputtering for these elements. The XPS chemical state analysis of the N 1s spectra after GCIB sputtering revealed a 17% damage ratio of altered nitrogen chemical state species. Further optimization of the GCIB sputtering conditions should lead to lower nitrogen damage ratios with the elemental concentrations closer to those of bulk PI.

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Recent reports in the literature have suggested that Si2N2O forms in the oxidation of Si3N4 as a buffer suboxide below the silica crust, and that equilibrium between SiO2 and Si3N4 requires the presence of this buffer. Here we report the examination of SiO2/Si3N4 boundaries of different genesis, by a variety of techniques, all of which failed to detect Si2N2O. What was found in each case is a graded suboxide whose composition merges seamlessly with the higher oxide above and the Si3N4 below. Part I presents the results of compositional depth profiling across the suboxide. In Part II a model is proposed to explain how O2 diffusion in the graded suboxide limits Si3N4 oxidation kinetics.