Ultrahigh frequency microplasmas from 1 pascal to 1 atmosphere

The generation of plasma-on-a-chip is examined for two extremes in gas pressure. The application of microplasmas as sensors of industrial vacuum processes requires stable operation at gas pressures of less than 1 Pa. In this low-pressure regime, the addition of a static magnetic field that causes electron cyclotron resonance is shown to increase the emission intensity of the microplasma by 50%. Using atomic emission spectrometry, the detection of helium in air is found to have a detection limit of 1000 ppm, which is three orders of magnitude worse than the DL of SO2 in argon. The loss of sensitivity is traced to the high excitation energy threshold of He, and to the poor ionization efficiency inherent in an air plasma. At atmospheric pressure (105 Pa), a microdischarge is described that operates in a 25 mm-wide gap in a microstrip transmission line resonator operating at 900 MHz. The volume of the discharge is ~10-7 cm3, and this allows an atmospheric air discharge to be initiated and sustained using less than 3 W of power.