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.

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Obtaining high resolution x-ray photoemission spectroscopy (XPS) spectra of insulating samples has long been a problem because of difficulty controlling sample surface potentials. A flood of low energy electrons has traditionally been used to control surface potential, but as monochromatized instruments with small, intense x-ray beams have become available, control has become much more difficult, particularly on larger samples. Increasing the current or energy from the flood gun does not improve the control appreciably. To understand the charging effect in a quantitative way, we have conducted some experiments with a test sample, configured to approximate the geometry present in several commercial XPS instruments using focused x-ray sources. These results show that, because of the energy spread of the flooding electrons, a negative potential is induced by the flood gun in the region surrounding the x-ray beam. This negative potential repels electrons, inhibiting the adequate neutralization of many samples. Based upon an analysis of these results, a neutralizing system is described in which a high current density flood gun with a narrow energy spread (to reduce potential variation on the sample) is used in combination with a source of low energy positive ions (to neutralize the negative potential in the peripheral region). This system has been tried on a wide variety of insulating samples in three commercial instruments, and found to give reproducible spectra with narrow linewidths. We present here spectra taken with the instrument offering the smallest and brightest x-ray beam, the most challenging case of the instruments tried.

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