Microfabricated inductively coupled plasma-on-a-chip for molecular SO2 detection: a comparison between global model and optical emission spectrometry

In this work the molecular SO2 detection limit obtained using a microfabricated inductively coupled plasma-on-a-chip (mICP) system is compared with a volume-averaged plasma model. The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminium vacuum chamber. The plasma operates from 0.1 to 10 Torr, and requires less than 4 W of power at a frequency of 493 MHz. Molecular detection limits were measured using the SO2 MUV2 band (A(1B1), a(3B1) → X(1A1)). Detection limits improve with increase of both the operating power and pressure due to increases in electron and metastable state Ar densities, with the best DL value being 45 ppb. A global plasma model is developed to calculate the metastable Ar density, electron temperature, and SO2 excitation rates in the mICP. Excitation rates for electron-impact collisions and the quenching reaction with Ar metastables, together with the known sensitivity of the optical system, allow one to calculate detection limits for molecular SO2 excitation. Calculated DLs are in reasonable agreement with experimental OES results.

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