A novel ToF-SIMS operation mode for improved accuracy and lateral resolution of oxygen isotope measurements on oxides

Abstract

Oxygen isotope exchange with subsequent time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a highly valuable tool for determining oxygen diffusion coefficients in oxides. Since ToF-SIMS analysis enables an elemental and chemical mapping, it can also be used to visualize oxygen exchange-active zones by determining the local oxygen isotopic fraction. However, measuring accurate isotopic fractions can be a challenging analytical task owing to secondary ion interaction and signal saturation, particularly when dealing with high secondary ion intensities as commonly found when analyzing oxygen ions from oxides. It is shown that in many cases the calculated 18 O À fraction erroneously shifts to higher values and can lead to systematic errors in the determination of diffusion coefficients. A novel ToF-SIMS operation mode, called "Collimated Burst Alignment" (CBA) mode, is therefore introduced to enable a more accurate determination of oxygen isotopic fractions with an optimized lateral resolution of sub-100 nm. Both improvements are rendered possible by a modified beam guidance in the primary ion gun. This modification reduces detector dead time effects and ion interactions to a minimum and secondary ion intensities can be obtained more accurately. The result of this optimization is demonstrated in measurements of the natural isotope abundance of several different oxides including SrTiO 3 and Sr-doped LaCoO 3 .

CHILI – the Chicago Instrument for Laser Ionization – a new tool for isotope measurements in cosmochemistry

“…Detector dead time is a well-known problem in time-of-flight mass spectrometry, and correction methods based on Poisson statistics have been developed [40] and are now standard protocol in quantitative TOF-SIMS analysis [4,41,42]. An interlaboratory study involving 21 TOF-SIMS instruments has demonstrated that this correction is generally applicable and robust [43].…”

Accurate and Precise Measurement of Oxygen Isotopic Fractions and Diffusion Profiles by Selective Attenuation of Secondary Ions (SASI)

“…32 This can be improved by bursting the beam in a similar way to that used in the "burst mode" measurements. This also has the effect of further decreasing the time-averaged primary current.…”

“…It would be possible to mitigate the saturation of 16 O which leads to the inaccurate value for C1 by further reducing the PI current (note we used a pulsed current of 0.068 pA@50 μs, which is at the low end of the range 0.03−0.05 pA @100 μs specified by Holzlechner et al). 32 However, decreasing the PI current further would decrease the precision of the measurement of 18 O SI intensity, adversely affecting the precision of the measured C1. Both BA and CBA modes avoid dead-time effects in the detector by decreasing the PI intensity, which enables the detection of the species with high ion yields and/or high concentration, such as 16 O, by globally decreasing the intensity of the spectrum.…”

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) imaging of deuterium assisted cracking in a 2205 duplex stainless steel micro-structure

“…The measurements were carried out on a TOF-SIMS IV instrument (ION-TOF GmbH, Muenster, Germany). A pulsed bismuth primary ion gun (25 keV, Bi 3 þ þ ) was used in the "collimated burst alignment" (CBA) mode enabling high lateral resolutions below 100 nm [18,27]. Additionally, to ToF-SIMS imaging in the CBA mode, high mass resolution spectra were acquired using the high current bunched mode (HCBU) to differentiate contributions of H 2 À and D À and OH 2 À and OD À secondary ions (SI) to the peaks at m/z ¼ 2 and m/ z¼18, respectively.…”