Barrier discharges (BDs) can be operated in so-called diffuse modes. In contrast to the usual filamentary regime, which is characterized by a large number of individual microdischarges, the plasma of a diffuse BD covers the entire electrode area uniformly. Depending on the operation conditions (gas composition, amplitude and frequency of applied voltage), different diffuse modes can be investigated, namely, the atmospheric pressure Townsend discharge (APTD) and the atmospheric pressure glow discharge (APGD). The subject of the paper is the study of the transition between APTD and APGD as well as between diffuse and filamentary BD modes. Therefore, BDs were studied in the gas mixtures N2/H2, N2/He, N2/Ne and N2/Ar. It is shown that APGD in the noble gases helium and neon is formed due to high ionization rate at a comparatively low electric field, assisted by indirect ionization mechanisms involving metastable states of inert gases and nitrogen impurities, while the existence of APTD is coupled to the existence of metastable states of molecular nitrogen. Furthermore, a similar memory effect of residual surface charges on the dielectric barriers as described for filamentary BDs was observed in diffuse BDs.

The atmospheric pressure glow discharge burning in nitrogen with small admixture of organosilicon compounds such as hexamethyldisilazane or hexamethyldisiloxane was used for the deposition of thin organosilicon polymer films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, infrared transmission measurements, ellipsometry, depth sensing indentation technique and contact angle measurements. The films were polymer-like, transparent in the visible range, with uniform thickness and without pinholes. The film hardness varied from 0.3 to 0.6 GPa depending on deposition conditions, the elastic modulus was in the range 15–28 GPa and the surface free energy was in the range 26–45 mJ m−2. The studied films exhibited good adhesion to the substrate.

Diffuse dielectric barrier discharges in neon and helium at atmospheric pressure were studied. The discharges were generated between two metal electrodes, both covered by an alumina layer and driven by ac voltage of frequency 10 kHz. The discharge gap was 2.2 mm and 5 mm, respectively. The discharges were investigated by electrical measurements and by temporally and spatially resolved optical emission spectroscopy. The experimental results revealed similar discharge behaviour in both gases being considered. Although the discharges were ignited at slightly different electric field strengths, their evolutions were found to be similar. At maximum discharge current the spatial light intensity distribution was characterized by the formation of a cathode fall. A difference was observed in the magnitudes of the current density only. In addition to the regime with a single discharge pulse per voltage half period T /2, a discharge mode with two and more subsequent current pulses per T /2 (also referred to as the pseudoglow discharge regime in the literature) was obtained due to an increase in the voltage amplitude or an admixture of nitrogen.

To cite this version:DAbstract. The atmospheric pressure dielectric barrier discharge burning in nitrogen with small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, the substrate temperature during the deposition process was elevated up to values within the range 25 • C -150 • C in order to obtain hard SiO x -like thin films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterised by Rutherford backscattering and elastic recoil detection methods, x-ray photoelectron spectroscopy, infrared spectroscopy measurements, ellipsometry and depth sensing indentation technique. It was found that the films properties depend significantly on substrate temperature at deposition. An increase of substrate temperature from 25 • C to 150 • C leads to an increase of film hardness from 0.4 GPa to 7 GPa and the film chemical composition changes from CH x Si y O z to SiO x H y . The films were transparent in visible range.

An atmospheric pressure glow discharge (APGD) was used for surface modification of polyethylene (PE) and polypropylene (PP). The discharge was generated between two planar metal electrodes, with the top electrode covered by a glass and the bottom electrode covered by the treated polymer sample. The discharge burned in pure nitrogen or in nitrogen-hydrogen or nitrogen-ammonia mixtures. The surface properties of both treated and untreated polymers were characterized by scanning electron microscopy, atomic force microscopy, surface free energy measurements and x-ray photoelectron spectroscopy. The influence of treatment time and power input to the discharge on the surface properties of the polymers was studied. The ageing of the treated samples was investigated as well. The surface of polymers treated in an APGD was homogeneous and it had less roughness in comparison with polymer surfaces treated in a filamentary discharge. The surface free energy of treated PE obtained under optimum conditions was 54 mJ m −2 and the corresponding contact angle of water was 40˚; the surface free energy of treated PP obtained under optimum conditions was 53 mJ m −2 and the contact angle of water 42˚. The maximum decrease in the surface free energy during the ageing was about 10%.