Plasma polymerization in RF capacitive coupled discharge in acetylene*

We investigated nanoparticles formed in the plasma volume of RF discharge in acetylene. The experiments were carried out in discharge tube with vertically arranged electrodes. It was found that the polymer film deposited on vertical electrodes includes nanoparticles with diameter of about 10 nm, and there are no larger nanoparticles in the film. On the tube wall the polymer film is also deposited, as well as nanoparticles with diameter of the order of several hundred nm. These nanoparticles were held in the plasma volume by the ambipolar field and have fallen on the tube wall when the combined action of gravity and ion drag force were able to overcome the near-wall potential barrier. The emission spectra measured near the boundary of the near-electrode layer contain almost only lines of atomic and molecular hydrogen, as well as CH molecular band (431 nm) with a weak intensity. It is shown that short-wave radiation (in the blue part of the spectrum) is strongly absorbed by the grown polymer film, while the lines in the red and infrared parts of the spectrum are weakly absorbed. The effect of a "vacuum pump" is observed, the gas pressure after the ignition of the RF discharge rapidly decreases several times compared to the initial one. Acetylene molecules are effectively incorporated into the growing polymer film on the electrodes and into the growinging nanoparticles in the plasma volume, while a small amount of hydrogen is released.