Experimental characterisation of atmospheric pressure electron gun

Abstract In this work, we present the results of an experimental study focused on characterisation of an electron gun designed for atmospheric pressure ionisation - Atmospheric Pressure Electron Gun (APEG). The APEG generates electrons with energies of several keV and could be used as replacement for β-radiation-based ionization sources for Atmospheric Pressure Ionisation (API) in Ion Mobility Spectrometry (IMS) or Mass Spectrometry (MS). In present work we have used Si 3 N 4 membranes with thicknesses of 100 and 150 nm as vacuum–atmosphere separators. For different initial electron energies we have measured electron currents, electron energy distribution functions, and electron energy after the transmission through the membrane. We have also tried to improve the electron transmittance characteristics of the APEG by modification of the membranes by deposition of thin gold films (2.5 to 10 nm), with only the 2.5 nm film achieving an improvement. Finally, we have investigated performance of APEG in air at atmospheric pressure achieving ion currents from 2.5 to 4 μA for 10 keV electrons and found similar thresholds for electron penetration in both the positive and the negative mode of 2.6 and 3.4 kV using the 100 and 150 nm membranes, respectively.