Design, manufacture, and applications of high mass resolution orbital trapping for secondary ion mass spectrometry

Abstract

Secondary Ion Mass Spectrometry (SIMS) is a widely used analytical technique for characterizing surface chemistry in numerous technical applications, including medical implant surfaces, fault-finding in semi-conductors, proteomics, pharmaceutical development, and in the field of astrobiology and the search for extra-terrestrial life. The mass resolving power of modern time-of-flight SIMS (ToF-SIMS) instruments does not exceed 12,000. This means that for some mass spectral peaks, a single molecular formula cannot be definitively specified. This is particularly important for high mass molecules, where there can be many possible peak attributions for a given nominal mass. Orbital ion traps have been shown to achieve mass resolution in excess of 100,000, without the need for the large and expensive superconducting magnets required in Fouriertransform ion cyclotron resonance (FT-ICR) instruments. Therefore, an orbital ion trapping mass analyser has been designed, fabricated, and coupled to the Ionoptika J105 SIMS. Computational modelling has been developed to evaluate proposed designs and examine the effects of manufacturing imperfections on the performance of the orbital ion trap. A method of exciting a precise mass range of trapped ions has also been developed, using a Stored Waveform Inverse Fourier Transform (SWIFT) technique. This allows fast, high mass resolution analysis after a low-resolution spectrum has been gathered using the time-of-flight analyser. This thesis will cover the function and capabilities of the Ionoptika J105 SIMS, the need for high mass resolution in SIMS, the mathematical background of electrostatic harmonic ion traps, and the simulation, design, manufacture, and operation of the orbital trapping mass analyser. This research allows mass spectra to be gathered with both high mass and spatial resolution, an advancement with numerous potential applications, including labelfree biological imaging and the unambiguous identification of biosignatures in astrobiology.