The Detection of Chemical Vapors in Air Using Optical Emission Spectroscopy of Pulsed Microdischarges From Two- and Three- Electrode Microstructures.

Emission spectroscopy of plasma-excited chemical species is widely used for generalized chemical analyses in bench-top systems. This paper explores the use of pulsed microdischarges between two and three electrode microstructures, which operate in air at atmospheric pressure, for use in handheld chemical analyzers. Pulsed microdischarges are fired between two-electrodes spaced apart by 0.2-2 mm. Synchronized optical sampling and time resolved spectroscopy are performed to capture the emission spectra from the microdischarge and its afterglow. The discharge spectra in air consist mainly of wide-band background spectra and line spectra from the nitrogen, and water vapor in air. The detection of vapors in air is limited by the relative strengths of representative lines compared to background spectra rather than by their absolute strength. The separate temporal characteristics of the line and background spectra present opportunities to improve detection. This concept is evaluated using isopropyl alcohol vapors (100 ppm) for which lines corresponding to CH fragments are detected with a handheld spectrometer despite the presence of air spectra. This paper also introduces a three-electrode (flashFET) configuration, which further reduces power consumption and electrode wear. Occupying an active area < 1 mm2, it employs a strategically located high-impedance gate electrode that permits the use of pulses < 100 V between the source and drain. The device consumes only 2.5 muJ/pulse at 140 Torr and 22.5 muJ/pulse at atmosphere, as compared to 470 muJ/pulse for two-electrode discharges. The operation of the flashFET as a gas sensor is evaluated using acetone vapors in air ambient. A response curve is obtained by measuring the 388.1 nm emission from acetone fragments for acetone concentrations ranging from 50 to 1000 ppm. [ABSTRACT FROM PUBLISHER]