Mass scale calibration of TOF‐SIMS spectra with molecular ions of internal additives

Abstract

The applicability of internal additives for mass scale calibration in time-of-flight secondary ion mass spectrometry (TOF-SIMS) was studied. Relation between the ions selected for mass scale calibration and the relative mass accuracy of the target molecular ions was investigated. Didecyldimethylammonium bromide (dC10DMA + Br À ), dioctadecyldimethylammonium chloride (dC18DMA + Cl À ) and tetradecyltrimethylammonium chloride (C14TMA + Cl À ) as target molecules and octadecyltrimethylammonium chloride (C18TMA + Cl À ) as an internal additive were prepared for positive TOF-SIMS spectra. Tinuvin 770 as a target molecule and sodium hexadecyl sulfate (C16OSO3 À Na + ) as an internal additive were used to evaluate negative TOF-SIMS spectra. In the case of dC10DMA + Br À , dC18DMA + Cl À and Tinuvin 770, the relative mass accuracy of the target molecular ions tends to be improved by mass scale calibration using the molecular ion of the internal additive. The relative mass accuracy of the molecular ion of the target ensured by the mass scale calibration using internal additives was less than approximately ±46 ppm. In some cases, however, internal additives highly effect on samples and change the sample properties because of coverage of the sample, removing a target molecule or causing matrix effects. It is necessary to evaluate the influence of the internal additive addition before applying internal additives. The detection of target ion peak should be especially confirmed after the addition of the internal additive. When samples are not influenced by internal additive addition, the internal additive method is effective for accurate mass calibration.