Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

Abstract

Understanding chemical kinetics of precursor dissociation and other follow-up plasma chemical reactions at atmospheric pressure plasma conditions is very important area of research for the development of plasma based film coating processes. It is very useful especially for coating on complex geometries like tubes, bottles, etc. Coating thin films on inner surface of tubes improves their functionality in many ways without changing the bulk properties. It improves the value of commercial tubes by improving their surface properties such as hydrophilicity, corrosion or permeation resistance and biocompatibility as in the following cases, 1. Depositing the fluorinated carbon on PVC tubes enhances the biocompatibility for the blood circulating tubes (Babukutty et al., 1999; Prat et al., 2000), 2. Silica coating on PTFE tube increases the wettability of the tube about 3 times (Yoshiki et al., 2006), 3. Carbon or titanium nitride film as protective coating on inner surface of a metallic tube improves its lifetime (Fujiyama, 2000; Hytry et al., 1994; Wang et al., 2008), 4. Deposition of silica on inner surface of PET tubes or bottles reduces the permeation of gases (Deilmann et al., 2008, 2009), 5. Titania coating on inner surface of glass tube improves its surface properties to be suitable for microfluidic devices (Yoshiki & Mitsui, 2008; Yoshiki & Saito, 2008), 6. Coating of nickel/alumina film on inner surface of silica tube and plasma treatment of resultant film increases the catalytic activity of this film for carbon nanofiber synthesis (Agiral et al., 2009). There are many ways film can be coated on various objects. Among those, “cold” plasma based film coating methods have many advantages compared to the conventional thermal film coating methods and spray coating methods. In plasma coating methods, electron will have high temperature (a few eV); however, atomic and molecular species will have low temperature (0.1 eV). Because of this, precursors can be dissociated at relatively low gas temperature through electron impact. Hence, the plasma technology can be used for film coating on thermo-labile plastic materials. The advantage of using atmospheric pressure plasma source for film deposition is that it does not require vacuum system and hence it is economically favourable method of film coating. Especially for thin film deposition on inner surfaces of tubes, atmospheric pressure plasma is more suitable than low pressure plasma. In this regard, several research groups have developed this process and coated various films like SiO2 and TiO2 on inner surface of various metal, quartz, PET and PTFE tubes (Agiral et al., 2009; Babukutty et al., 1999; Deilmann et al., 2008,