Potential of gas-assisted time-of-flight secondary ion mass spectrometry for improving the elemental characterization of complex metal-based systems

Abstract

Enhancing the spatial resolution of Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), which provides 3D elemental distribution in combination with high sensitivity and molecular information, is currently one of the hottest topics in the field of chemical analysis at the nanoscale. As the efficiency of the ionization process determines the possibility of imaging a sample's elemental structure in 3D, methods for enhancing secondary ion generation are of particular interest. Recently, a novel approach of combining a high-vacuum compatible compact TOF-SIMS detector with a Gas Injection System (GIS) integrated within a Focused Ion Beam (FIB) instrument has been demonstrated on pure metals. In this work, we present a comprehensive study on water vapor and fluorine gas-assisted TOF-SIMS conducted on dedicated Zr-based model samples (ZrAl, ZrSi and ZrCu) to verify whether the application scope of this method can be expanded to more complex alloys. The main concerns of potential preferential sample sputtering and sample isotope abundance content degradation caused by the introduced gas were excluded. Moreover, fluorine gas improved the accuracy of the measured Zr isotope contents. In most cases, the ion yields were significantly increased. Furthermore, gas co-injection seemed to mitigate variations in element ionization along the thin film, allowing us to obtain more representative TOF-SIMS data regarding sample composition. Compared to the results obtained under standard vacuum conditions, the alloys' sputtering rates decreased by up to 46% when using water vapor and almost doubled in the case of fluorine gas.