| Although low-pressure plasma discharge has been used in material process for years, the precursors for the process are limited only in gas phase. In order to enhance the versatility of the process, the technique of direct liquid injection into low-pressure plasma was proposed by our group. The technique enables the use of liquid precursors, e.g. ethanol and hexane, etc. Furthermore, the technique also realizes the feeding of powders though a fluid into a reactor, e.g. metals, dielectrics, aromatics, proteins, viruses, etc. This means that the technique can potentially improve the various properties of a film. In this dissertation, several investigations of the plasma and the droplets under this technique were firstly made. Firstly, the theoretical background for this technique will be shown. Although the conventional theories were compiled, this will still be worthwhile to give some directions for future researchers. Next, the variation of the plasma by direct droplet injection will be shown. Due to the droplet evaporation, the time-variable plasma was inevitable. In this investigation, the analyses of the plasma were made by observing the variations of the chamber pressure, the operating powers, the plasma density, the electron temperature and the optical emissions. Toward the analysis of the plasma by droplet injection, four kinds of injection were made in order to gradually add complexities. When droplets were injected, the large variations of plasma parameters were observed. In particular, the plasma density was significantly decreased, which partially caused the absence of the droplet variation. Finally, the variation of the size and the temperature of droplets by direct droplet injection will be shown. For the study of the droplet size, a droplet size analyzer (SprayTecRTM) was used. Due to the high speed of droplets and the lack of the plasma density, the droplet size remained constant even when they went through plasma. For the study of the droplet temperature, the technique called two-color laser-induced fluorescence (2cLIF) was used with an organic dye (rhodamine b.) The measurements showed the decrease of the temperature at low pressure. However, they had significant temperature off-set so that they miss something. |
