Feasibility study of material surface modification by millimeter size plasmas produced in a pin to plane electrode configuration D.B. Kim, J.K. Rhee, S.Y. Moon, W. Choe ⁎ Department of Physics, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea Available online 4 December 2006 Abstract A few millimeter size plasma was generated in a pin to plane electrode configuration with either Aluminum or Indium Tin Oxide glass. Depending on the plane electrode material, the plasma showed either corona or corona-dielectric barrier discharge hybrid discharge characteristics. From electrical and optical diagnostics, it was found that the hybrid discharge was more electrically stable and had lower rotational temperature. A feasibility study of material surface modification was performed with the hybrid discharge. All samples such as polyethylene and polypropylene films became more hydrophilic, and the surface property was changed only within the radius of less than about 12 mm. In addition, several effects of gas temperature and treatment time on the surface modification were studied besides the durability. © 2006 Elsevier B.V. All rights reserved. Keywords: Atmospheric plasma; Corona-DBD hybrid plasma; Surface modification 1. Introduction Plasma treatment is one means of modifying polymer sur- faces to improve their adhesion as well as to provide bio- compatibility of materials such as polyvinyldifluoride (PVDF), phosphorous glass (SiPOC), and polyvinyl chloride (PVC) [1,2]. Plasmas are attractive for surface modification, because they change surface properties without affecting the favorable bulk characteristics. Also, the plasma surface modification process is usually fast and is a dry process. Thus, the plasma modification of polymer surfaces is becoming more highly utilized [3]. The most general plasma type for the surface modification has been the corona involving dielectric barrier discharges (DBD). The nature of plasma interaction with various polymer surfaces is determined by plasma source configuration and operating parameters, therefore, a proper selection of electrode configu- ration, power supply design, and supply gas help minimize or even eliminate the filamentary discharges, which often lead to a nonuniform surface treatment, and it also helps generating glow discharges instead. Considering the discharge regime is an important issue as it can have a significant effect on the surface modification by changing both the ratio of electrons to metastables and the spatial distribution of active species [4]. It was actually shown that wettability of the polypropylene was increased greater by a glow DBD than by a filamentary DBD [5]. On the other hand, there is sometimes a need for a local or small area surface treatment. Therefore, a pin to plane electrode type was chosen in this work to generate a glow discharge of small size. The plane electrode was either an Aluminum con- ductor or an Indium Tin Oxide (ITO) glass for the study of dielectric effects on the discharge characteristics. Then, a feasibility study for plasma surface modification was performed for various materials, mostly polymers, with the ITO glass plane electrode, which gave better discharge characteristics for the surface modification. 2. Experimental setup Fig. 1(a) shows the experimental setup with a pin to plane electrode configuration. The copper pin electrode (1) of 360 μm in radius was located in a cylindrical pyrex tube (2) of 3 mm in radius. The plane electrode (3) was either an Aluminum con- ductor or an ITO glass (thickness of 0.7 mm) that was connected to ground through a 50 Ω shunt resistor (4) to measure current. All experiments were performed at the atmospheric pressure in the ambient air. The chemically 99.99% pure helium gas (5) was Thin Solid Films 515 (2007) 4913 – 4917 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: wchoe@kaist.ac.kr (W. Choe). 0040-6090/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2006.10.069