Ultrahigh frequency microplasmas from 1 pascal to 1 atmosphere

Abstract

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 µm-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.