Microdischarges in a barrier discharge with an asymmetric electrode arrangement (‘metal–dielectric’) were investigated with fine temporal (down to 10 ps) and spatial (down to 10 µm) resolution by the technique of cross-correlation spectroscopy. The discharge was operated in dry air at atmospheric pressure. The spatio-temporal distributions of the light intensities of the 0–0 transitions of the second positive (λ = 337.1 nm) and first negative (λ = 391.5 nm) systems of molecular nitrogen were compared with the corresponding experimental results for a symmetric electrode arrangement (‘dielectric–dielectric’) and for the coplanar barrier discharge. For all the discharge types being considered, the mechanism of electrical breakdown was found to consist of the Townsend pre-breakdown phase, the phase of ionizing wave propagation and the decay phase. Despite the qualitative similarity of the microdischarge development in different electrode arrangements, a detailed comparison of certain discharge characteristics (ionizing wave velocity, spatially or temporally integrated light intensity) enables us to reveal the influence of the electrode configurations on the process of electrical breakdown.

The barrier discharge in the coplanar arrangement operating in a single-filament mode was studied spectroscopically. The evolution of the discharge luminosity was measured by the technique of cross-correlation spectroscopy. The 1D-spatially and temporally resolved luminosities of the first negative (at 391.5 nm) and the second positive (at 337.1 nm) system of molecular nitrogen were recorded using the above-mentioned technique. A cathode-directed ionizing wave (IW) was clearly seen on the plot for radiation intensity at 337.1 nm. In addition to this, also observed was a wave of the enhanced electric field propagating over the anode. In this paper, the propagation of these waves is described and their velocities are determined. The discharge evolution is divided into three phases-the Townsend phase, the phase of the IWs propagation and the extinction phase. Since the above-mentioned luminosity distributions could be interpreted approximately as the electric field (for 391.5 nm) and the electron density (for 337.1 nm) distribution, the qualitative description of the discharge is made accordingly. All these parameters are compared with similar measurements of the volume discharge. Apart from this, an attempt to determine the reduced electric field is made according to the kinetic model.

Formation processes of negative ions in low-pressure plasmas are not yet fully understood: as a rule experiments reveal higher negative ion density than predicted by the models. In this work we report near-surface generation of negative ions. This hitherto neglected formation mechanism appears to be important in low-pressure discharges and can have large impacts on the bulk plasma chemistry. We monitor energy-resolved positive and negative ion fluxes arriving at the electrodes in an oxygen parallel-plate radio-frequency ͑rf, 13.56 MHz͒ and dc glow plasmas by means of a quadrupole mass spectrometer. Negative ions formed in the plasma volume are observed by extracting them through an orifice in the anode of a dc glow discharge. Unexpectedly, we record large negative ion signals at the cathode of a dc discharge and at the grounded electrode of an rf discharge. These ions are formed in the plasma sheath, in collision processes involving high-energy species. We propose an efficient mechanism of negative ion generation due to ion pair formation in the sheath.

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