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SIMS21, Poland 2017 - James C Hood abstract

James C Hood oral presentation (PB1-Mon2-1-2)

Optimal Stored Waveform Inverse Fourier Transform (SWIFT) Excitation in a SIMS Orbital Trapping Mass Analyser

James C Hood, Barry J Gallacher, Peter J Cumpson

Surface Engineering and Analysis Laboratory (SEAL), School of Mechanical & Systems Engineering, Newcastle University, Claremont Road, NE1 7RU Newcastle upon Tyne, United Kingdom


High mass resolution in secondary ion mass spectrometry (SIMS) has been widely sought over the past two decades, with hybrid instrumentation a promising avenue of research. One such example is the coupling of Fourier transform mass spectrometers with SIMS instruments, in the form of secondary ion Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) [1] [2]. FT-ICR MS allows access to higher mass resolution (m/Δm > 105) than is attainable with the time-of-flight (ToF) mass analysers (m/Δm ≈ 104), which are typically used in static SIMS.

Another potential SIMS FT mass analyser is the orbital trapping mass analyser[3,4], which we have designed and fabricated for our J105 SIMS instrument[3]. However, both ICR and orbital trapping analysers operate at a much slower repetition rate than ToF ones, with acquisition dwell times per pixel of the order of 100ms to several seconds, as opposed to as little as 10µs for modern ToFSIMS instruments such as the Ionoptika J105[5].

In both types of FT-MS the field which governs ion motion can potentially be manipulated by applying different voltages to the component electrodes, a process known in ICR-MS as Stored Waveform Inverse Fourier Transform (SWIFT)[6]. The time-domain excitation waveform is formed from the inverse Fourier transform of the appropriate frequency-domain excitation spectrum, which is chosen to excite the resonance frequencies of selected ions.

We have identified an optimum SWIFT signal for rapid high-resolution SIMS spectroscopy to improve the speed of performance of orbital trapping relative to ToF, while retaining very high mass resolution, meeting the specific needs of SIMS for high repetition rate and high mass resolution in a user-defined window.

References

[1] S Maharrey et al. Applied Surface Science 231–232, 2004, 972–975

[2] DF Smith et al. Analytical Chemistry 83(24), 2011, 9552–9556

[3] JC Hood et al. International Journal of Modern Engineering Research 6(10), 2016, 76–83

[4] A Pirkl et al. Microscopy and Microanalysis 22(Suppl 3), 2016, 340–341

[5] JS Fletcher et al. Analytical Chemistry 80(23), 2008, 9058–9064

[6] RB Cody et al. Rapid Communications in Mass Spectrometry 1(6), 1987, 99–102