Abstract
In study, we used atmospheric pressure plasma source (APPS) to study the effect of driving frequency on the characteristic of plasma, the effect of gas flow on the deposition process and plasma density distribution, deposition of organic silicon film, and controlling the pretilt angle of liquid crystals (LCs). The study was to investigate the driving frequency effects on the characteristics of atmospheric plasma jets system. The discharge gas is the helium. We change the power source frequency range from 10 MHz to 20 MHz. As the driving frequency is increased, we can observe the several phenomena. (1) gas breakdown voltage from 256 V down to 204 V, (2) plasma density from 0.798×?10?^12 ?cm?^(-3) rose to 2.218×?10?^12 ?cm?^(-3) and increase the current from 0.125 A to 0.224 A when the plasma state at highest α mode discharge, (3) sheath thickness decreased from 0.348 mm to 0.257 mm before discharge mode transition, (4) the electron excitation temperature dropped from 0.535 ev 0.316 ev when the plasma power of 25 W. Collectively, these results suggest that the high driving frequency help to improve the quality of plasma, enhance discharge efficiency, and make the atmospheric plasma jets systems have a wider application space.From the results, the gas flow distribution became non-uniform at helium flow rate of 5 slm. By modifying the structure of nozzle, the gas flow distribution became more uniform so that film deposition became uniform. Because the uniformity of film deposition is related to the plasma density distribution, the gas flow distribution effected the plasma density distribution. In study, the APPS was used to deposited the organic silicon film, HMDSO as the material. The process could control the structure and properties of the film. Results showed main bonds (Si–CH?3 and Si–O–Si) can be controlled by molecular average energy (W/FM). The ratio of Si–O–Si increased when W/FM became large. The ratio of Si–CH?3 was increasing with decreasing the W/FM. Si–O–Si are polar bonds, and Si–CH?3 are non-polar bonds. Thus, if the ratio of Si–O–Si was higher than Si–CH?3, the film became hydrophilic (surface energy could be 68 mJ/m2) and surface hardness became hard. If the ratio of Si–CH?3 was higher than Si–CH?3, the film became hydrophobic (surface energy could be 25 mJ/m2) and surface hardness became soft. The pretilt angle of LCs could be controlled by adjusting the surface energy of the film. When the surface energy was smaller than 34 mJ/m2, the pretilt angle approached 90o. When the surface energy was larger than 60 mJ/m2, the pretilt angle approached 0o. Therefore, the pretilt angle could be controlled by the range of surface energy from 34 to 60 mJ/m2.