Barrier discharges (BDs) produce highly non-equilibrium plasmas in a controllable way at atmospheric pressure, and at moderate gas temperature. They provide the effective generation of atoms, radicals and excited species by energetic electrons. In the case of operation in noble gases (or noble gas/halogen gas mixtures), they are sources of an intensive UV and VUV excimer radiation. There are two different modes of BDs. Generally they are operated in the filamentary one. Under special conditions, a diffuse mode can be generated. Their physical properties are discussed, and the main electric parameters, necessary for the controlled BD operation, are listed. Recent results on spatially and temporally resolved spectroscopic investigations by cross-correlation technique are presented. BDs are applied for a long time in the wide field of plasma treatment and layer deposition. An overview on these applications is given. Selected representative examples are outlined in more detail. In particular, the surface treatment by filamentary and diffuse BDs, and the VUV catalyzed deposition of metallic layers are discussed. BDs have a great flexibility with respect to their geometrical shape, working gas mixture and operation parameters. Generally, the scaling-up to large dimensions is of no problem. The possibility to treat or coat surfaces at low gas temperature and pressures close to atmospheric once is an important advantage for their application.

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This paper introduces a plasma reactor for short-time plasma surface modification of polymer powders. This reactor type, the so-called plasma downer reactor (PDR), provides a high reaction rate, which is forced by the high gas velocity and high particle dispersion in the plasma. It combines the advantageous characteristics of the downer principle for the fluid dynamics of gas-solid phases with plasma surface modification. This work demonstrates that a very short plasma exposure time of 0.1 s effectively improves the wettability of HDPE and Co-PA powders. The water contact angles of HDPE and Co-PA powder can be reduced to 72 and 76, respectively. The surface tensions of both polymer powders could be increased by a factor of 2 up to 43 mN/m. Water/polymer suspensions and pastes can be made without tensides.

Cover: Plasma surface processing is used to overcome agglomeration of dry find powders and meet the demand for homogenously functionalized powder particle surfaces. The cover shows a scheme for a down‐stream reactor designed for efficient surface modification and functionalization of particulates. Further details can be found in the article by A. Sonnenfeld, A. Spillmann, C. Arpagaus, and Ph. Rudolf von Rohr* on page 170.

A low pressure radio frequency discharge was used to deposit films by mixtures of oxygen and titanium (IV) isopropoxide (TTIP) at powers of 200 W on films of polyethylene-terephthalat and samples of quartz glass. In the non-thermal plasma, films of rather pure TiO 2 could be deposited as revealed by X-ray photo-electron spectroscopy. Besides the film growth rate and the chemical composition, the spectral behaviour of the spectral transmittance of visually transparent films was determined in the range from 200 to 500 nm. Furthermore, the absorptance of films has been derived at characteristic spectral positions of the transmission spectra of the films. Accordingly, cut-off wavelength was found to increase with deposition time from 5 to 10 min as well as with the concentration of TTIP in a range below 1.7%. At 310 nm, the spectral absorption coefficient (extinction coefficient × concentration) was 12 µm −1 . While keeping other parameters constant, this coefficient decreased by 4 µm −1 due to an increase of the concentration of TTIP from 1.7% to 8%. Simultaneously, the surface roughness increased as revealed by profilometry. Thus, since the chemical structure of films was found to change only marginally, a decrease of the film density is likely to cause the observed dependence of the absorption coefficient with increasing precursor concentration.

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The surface of microscopic lactose particles was modified by gas phase reactions occurring during a PECVD process to improve the flow behavior of the powder. The particulates were exposed to a capacitively coupled O2/Ar/HMDSO RF discharge in a down stream reactor by varying the gas composition and the RF power. The flowability and the surface free energy of the powders were determined by a ring shear tester and by a tensiometer, respectively. Based thereon, the change in surface free energy was determined not to be the dominating factor for the significantly enhanced flowability of the plasma‐treated powder. Rather, the flowability improvement is supposed to be affected principally by the plasma‐induced change in particle surface roughness.