Low-pressure non-equilibrium plasma technologies: scientific background and technological challenges

Abstract The scientific background of low-pressure, non-equilibrium plasma technologies is presented. An electrical discharge heats free electrons, which create reactive plasma species (molecular radicals, ions, and radiation) at endothermic inelastic collisions with the source gas molecules in the gas phase. The lack of channels for the loss of species in the gas phase at low pressures enables a rather large density of species in the bulk plasma even at low discharge power density, and thus a large flux onto the surfaces, where exothermic reactions occur. The type and intensity of surface reactions depend on the fluxes and the dose of reactive plasma species. Measuring the surface modification versus the dose of species enables a solid scientific background for the development of desired plasma technology. Once the scientific background is sufficient, the upscaling to large devices and mass application is only a technological challenge, which includes the plasma uniformity in industrial-size reactors, the spontaneous drifting of plasma parameters due to changes in the surface coefficients, and unwanted effects that often arise from over-treatment. Both the scientific and technological challenges are highlighted, and directions for further research are presented in this article.