MTL Annual Report

Figure 1: Testing jig for the carbon-nanotube-based electron impact ionizers.

The Micro-Gas Analyzer Project attempts to leverage the cost reduction, performance enhancement, and increased portability associated with MEMS to create a microfabricated mass spectrometer for chemical species detection.  Mass spectrometers are powerful analytical instruments that are mainly comprised of an ionizer, a mass analyzer, a detector, and a vacuum pump.  Our group and collaborators have made substantial progress on these various components, spanning carbon-nanotube-based electron impact ionizers ^[1], chip-scaled quadrupole mass filters with square electrodes ^[2], and time-modulated capacitance electrometers ^[3].  Each component functions and performs adequately on its own, but a complete system requires the integration of these three parts, as demonstrated by other researchers ^[4] [5].

Figure 2: Mounted time-modulated capacitance electrometer made by our collaborators at the University of Cambridge, UK.

An integration plan was conceived to sequentially combine the various components in a logical manner.  A testing jig was designed and machined so the electron impact ionizers would have electrical connections to the power supplies and compatibility with our in-house characterization system.  After validating the functionality of the ionizer with a macro-scaled quadrupole and a Channeltron electron multiplier, we plan to use our chip-scaled quadrupole instead of the macro-version.  Once these two vital components are well characterized, we will check the functionality of the electrometer with a commercial ion source and a macro-scaled quadrupole.  Finally, we will put all three components together to be tested and characterized in a vacuum chamber.

1. L.F. Velásquez-García, B. Gassend, and A.I. Akinwande, “CNT-Based Gas Ionizers with Integrated MEMS Gate for Portable Mass Spectrometry,” in Technical Digest of Transducers, Denver, CO, June 2009, pp. 1646-1649. [↩]
2. K. Cheung, L.F. Velásquez-García, and A.I. Akinwande, “High Performance MEMS Square Electrode Quadrupole Mass Filter for Portable Mass Spectrometry,” Technical Digest of the 23^rd IEEE International Conference on Micro Electro Mechanical Systems MEMS 2010, Hong Kong SAR, China, pp. 867-870. [↩]
3. Y. Zhu, J. Lee, and A. Seshia, “System-level simulation of a micromachined electrometer using a time-domain variable capacitor circuit model,” Journal of Micromechanics and Microengineering, vol. 17, pp. 1059-1065, 2007. [↩]
4. R.A. Miller, E.G. Nazarov, G.A. Eiceman, and A.T. King, “A MEMS radio-frequency ion mobility spectrometer for chemical vapor detection,” Sensors and Actuators A, vol. 91, pp. 301-312, 2001. [↩]
5. E. Wapelhorst, J-P. Hauschild, and J. Müller, “Complex MEMS: a fully integrated TOF micro mass spectrometer,” Sensors and Actuators A, vol. 138, pp. 22-27, 2007. [↩]