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.