Entry Date:
November 8, 2018

Electron Impact Gas Ionizer with 3-D Printed Housing and NEMS Si Field Emission Cathode for Compact Mass Spectrometry

Principal Investigator Luis Velasquez-Garcia (Heller)

Mass spectrometry is widely used to quantitatively determine the composition of samples. However, the bulky size and high-power consumption of conventional mass spectrometry instruments limit their portability and deployability. One of the key components of a mass spectrometer (MS) is the ionizer. State-of- the-art electron impact gas ionizers use a stream of electrons produced by a thermionic cathode to create ions by fragmentation. Field emission cathodes, based on quantum tunneling of electrons triggered by high electrostatic fields, are a better alternative for portable mass spectrometry of gases compared to mainstream thermionic cathodes because they consume significantly less power, are faster to switch, and could oper- ate at higher pressure.

In this project, we are developing a compact electron impact gas ionizer based on a cleanroom- microfabricated cathode and a 3-D printed ionization housing. The cathode is an array of nano-sharp silicon field emitters with proximal, self-aligned extractor gate, while the ionization housing is composed of an ionization region surrounded by an ionization cage, an anode electrode, a repeller electrode, and a dielectric structure that holds together the electrodes. To produce ions (i) a high enough bias voltage is applied between the extractor gate and the silicon tips, shooting electrons into the ionization region, (ii) the anode electrode attracts the emitted electrons, forcing them to interact with the neutral gas molecules within the ionization region, (iii) the bias voltage of the ionization cage maximizes the ionization yield of the interaction between the electrons and the neutral gas molecules, and (iv) the repeller electrode pushes ions out of the ionization cage. We show an assembled ionizer. Current work is focused on characterization of the field emission cathode and gas ionizer at various conditions.