The design, development, and testing of a microfabricated, miniaturized magnetic sector mass spectrometer ("micro mass spectrometer") with a mass resolution of 1 atomic mass unit (amu), a mass range of 1 - 300 amu, and a sub part-per-billion (ppb) sensitivity to chemical species is proposed. The design of a distributed sensor network specifically for a system of such spectrometers will also be undertaken. The micro mass spectrometer has, as its enabling component, a icrofabricated, carbon nanotube (CNT) field-enhanced ionization source and ion optic lens, and designed so that the ion beam is oriented parallel, not perpendicular, to the substrate surface. Electron impact ionization and field ionization arrays will both be investigated. The proposed effort will focus on the development and testing of this device for applications in gas-phase environmental sensing. The team is comprised of a group of scientists from Duke University and MCNC-RDI, a microelectronics research and development institute. Scientists at Duke University bring expertise in surface science, field emission, and gas phase chemistry and will work in tandem with researchers at MCNC-RDI, who offer expertise in MEMS design and microfabrication, sensor development, and vacuum microelectronics. With respect to intellectual merit, the prime novelty and device concept are conveyed in Figure 1, showing a schematic representation of the proposed micro mass spectrometer and an SEM micrograph of a demonstrated field emission device. In addition to the design, development and microfabrication of this important sensor and its various components, the proposed research will enable an investigation of the subtle and important differences between field emitter and field ionization arrays within the same microsystem. An electron field emitter array will generate ions indirectly through electron impact ionization and dissociation and will have both energy and pressure dependences. Higher energies and pressures will lead towards more dissociation of the gaseous species, producing ion fragments at the detector. In contrast, direct, field-enhanced ionization is expected to be less sensitive to both energy and pressure, above a specific ionization threshold. A fundamental study of these parameters in addition to electrode materials and geometries and their combined effects on gas phase kinetics and ionization will lead to a greater understanding of sensor design and detector optimization. With respect to broader impact, this proposal focuses on environmental gas sensing applications; however with proper source characterization and system design, the technology can be used in applications ranging from chemical warfare agent detection to biomedical diagnostics. Also, the technology platform created by this research, an on-chip ion and/or electron workbench, can be applied to a number of far ranging applications, including ion propulsion for miniature spacecraft, miniaturized X-ray tubes, UV light sources, and microwave devices. The successful completion of this program will lead to a new fundamental understanding of microscale gas phase ionization, reaction kinetics, and ion measurement, as well as enabling the development of a new paradigm for analyzing and detecting chemical species in gaseous environments.
