Investigation Of Functional Films Deposition By Pulsed Dielectric Barrier Discharge At A High Pressure

Cold plasma surface treatment technology is widely used for its simple process, convenient operation, easy control and environment friendly. The films deposited by plasma have many special features such as: uniform, well adhesive, high cross-linkings, chemical stability and no negative effect on the substrate.Pulsed plasma is that the plasma consists of Ton (plasma-on) and TOFF (plasma-off) in each cycle. The Ton means the plasma is in discharging and provide sorts of radicals, and Toff means the discharge is off in the chamber but the polymerization is still happened during the Toff. So the films polymerized in pulsed plasma, the density of free radicals in the films will be small, the temperature of substrate will be low, the bombardment caused by the high energy ions will be decreased, functional groups in the films will be retained and the chemical characteristics of the film will be suitably selected and controlled in the pulsed plasma. If under proper conditions, both grafting and polymerization can be achieved simultaneously. The tiny thickness film can be deposited on the material with smooth surface without pin-hole, rough or porous.In this paper, we use a DBD pulsed discharge instead of Continue Wave discharge, polymerize a high -COOH retention film at a high deposition rate with acrylic acid or maleric acid as precursor. Through the polymerization and the property measurements of tfilms, the mechanism of the polymerization was discussed preliminarily. The main conclusions of this work are as follows:1. Different parameters including working pressure, duty cycle, power frequency, distance between electrodes and different locations of substrate on the electrode was studied. The results show the working pressure, duty cycle and power frequency are the main factors to role the characterization of the film. At the same time, the effects from latter two parameters are less.2. Functional films are deposited in DBD plasma using acrylic acid or meleric acid as monomer. Comparing with poly (meleric acid) film, higher density of functional groups is in poly (acrylic acid) film even it is worse stability. Both films are uniform and compact with water contact angle nearly at minimum of 3s, which is super hydrophilic surface.3. Stability experiments are carried out, which shows a contradiction behavior betweenstability and high retention of functional groups. The increase of electron bombardments is necessary for high cross-linkings and better stability of the film. However, the functional groups are destroyed and leaded a low retention of functional groups in the film.4. The quite stable discharge with the working pressure variation is concluded from current vs voltage figure. At the pressure of 300Pa, it's like a glow discharge and the discharge happened before zero voltage when the pressure increased.5. Electron temperature is measured by OES, which is about 0.65eV calculated from the spectroscopy.