Probing Ionization Energies for Trace Gas Identification: The Micro Photo Electron Ionization Detector (PEID)

Micro gas sensors detect the presence of substances, but can hardly identify them. We developed a novel approach of probing referenceable ionization energies. It extends the photoionization principle towards tunable energies via replacement of photons by accelerated photo electrons. The device comprises UV-LED illumination, an atmospherically stable photoelectron emission layer with a nano-vacuum electronics accelerator realized in thin film technology and charged particle measurement. A voltage variation at the accelerator provides electrons of tunable energies. The resulting system works at high pressures and reaches ambient laboratory air operability. We were able to prove that variable electron energies can be used for VOC detection using ethyl and butyl acetates, methyl mercaptan, alcoholes, DMSO and trichloro ethylene. The signals observed are resulting from ion scattering which overlays the original electron beam current and can be described borrowing from the old models of thyratron electron tubes and ion mobility spectrometers. The energy resolution which has been reached so far is 0,2 eV and is discussed with respect to the achievable performance data that have been estimated on the basis of theoretical considerations.