Mass Spectrometry Technologies for Spaceflight Applications

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2023

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The National Research Council’s Planetary Science 2013-2022 Decadal Survey underscores three interrelated themes pivotal to planetary science research: understanding solar system beginnings, searching for the requirements for life, and understanding the workings of solar systems. In situ mass spectrometry (MS) is the primary technique for the analysis of planetary substances, directly addressing the critical inquiries associated with these themes. The quintessential mass analyzer engineered for space exploration is envisioned to embody a suite of features: a mass range extending from 1 u to at least 500 u, capability for high-precision measurement of stable isotope ratios within a tolerance of ±1‰, and the ability to resolve distinct isobaric species at a low mass below 60 u, all with low power requirements. Incorporation of these capabilities within a single instrument is crucial for facilitating the exploration of the necessities of life and for advancing our understanding of solar system genesis and planetary development. Nevertheless, state-of-the-art existing spaceflight mass spectrometers do not fully integrate all these capabilities.In this research, three technologies are investigated to close this gap; spatial aperture coding, super-resolution, and field emission electron sources . The development of these three technologies as presented in this dissertation represent a significant step towards a mass spectrometer having all of the characteristics described above. First, Spatial aperture coding is a technique used to improve throughput without sacrificing resolution, historically in optical spectroscopy, and more recently as demonstrated by our laboratory at Duke University, in sector mass spectrometry (MS). Previously we demonstrated that aperture coding combined with a position-sensitive array detector in a miniature cycloidal mass spectrometer was successful in providing high-throughput, high-resolution measurements. However, due to poor alignment and field non-uniformities, reconstruction artifacts were present. In this dissertation, two methods were implemented to significantly reduce the presence of artifacts in reconstructed spectra. First, I employed a variable system response function across the mass range (10 – 110 u) instead of using a fixed function. Second, I modified the design by shifting the coded aperture slits relative to the center of the ionization volume to enable even illumination of the coded aperture slits. Both methods were successful in significantly reducing artifacts at low mass from above 35% of the peak height to less than 6% of the peak height. Second, higher resolution in fieldable mass spectrometers (MS) is desirable in space flight applications to enable resolving isobaric interferences at m/z < 60 u. Resolution in portable cycloidal MS coupled with array detectors could be improved by reducing the slit width and/or by reducing the width of the detector pixels. However, these solutions are expensive and can result in reduced sensitivity. In this dissertation, I demonstrate high-resolution spectral reconstruction in a cycloidal coded aperture miniature mass spectrometer (C-CAMMS) without changing the slit or detector pixel sizes using a class of signal processing techniques called super resolution (SR). I developed an SR reconstruction algorithm using a sampling SR approach whereby a set of spatially shifted low-resolution measurements are reconstructed into a higher-resolution spectrum. This algorithm was applied to experimental data collected using the C-CAMMS prototype. It was then applied to synthetic data with additive noise, system response variation, and spatial shift nonuniformity to investigate the source of reconstruction artifacts in the experimental data. Experimental results using two 1/2 pixel shifted spectra resulted in a resolution of 3/4 pixel full width at half maximum (FWHM) at m/z = 28 u. This resolution is equivalent to 0.013 u, six times better than the resolution previously published at m/z = 28 for N2+ using C-CAMMS. However, the reconstructed spectra exhibited some artifacts. The results of the synthetic data study indicate that the artifacts are most likely caused by the system response variation. Despite these artifacts, it was shown that the super-resolution algorithm is capable of resolving the isobaric interference between N2 and CO at m/z = 28. Third, Field emission electron sources for MS electron ionization have been of interest to spaceflight applications due to their low power compared to thermionic sources. However, state-of-the-art devices suffer from limitations such as high turn-on macroscopic field, low macroscopic current density, poor emission stability, and short lifetime. Field emitter arrays with a high spatial density of uniform emitters have the potential to address these problems. In this work, process development, fabrication, and testing of two novel field emission based devices are presented, including CNT array emitters and metallic nanowires. Instability in CNT emission was investigated using noise analysis and a polymer encapsulation process to reduce the effect of adsorbates on the tips of CNTs. This treatment was not successful in reducing emission noise in CNTs. Thus, electron beam lithography and templated electrodeposition were used to fabricate a high spatial density array of metallic nanowires, resulting in electron field emission with high macroscopic current density (2 A/cm2) and low turn-on macroscopic field (4.35 V/μm). Results indicate that templated electrodeposition of metallic nanowire arrays is a promising method for producing high-performance field emitters.

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Aloui, Tanouir (2023). Mass Spectrometry Technologies for Spaceflight Applications. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/30340.

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Dukes student scholarship is made available to the public using a Creative Commons Attribution / Non-commercial / No derivative (CC-BY-NC-ND) license.