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Table 1. Surface Modification Methods Physical Physical adsorption Langmuir-Blodgett film

Chemical Oxidation by strong acids [2, 3] Ozone treatment [4] Chemisorption [5] Flame treatment

Radiation Plasma (glow discharge) Corona discharge Photo-activation (UV) [6] Laser [7] Ion beam [8] Electron beam [9] y irradiation [10]

PLASMA DISCHARGE SURFACE MODIFICATION A glow discharge plasma is created by evacuating a vessel, usually quartz (for inertness), then refilling with a low pressure gas (see Fig. 1). The energetic species in a gas plasma include ions, electrons, radicals, metastables, and photons (short wave UV). The collision of these energetic species with the material surfaces results in the final surface modification. In addition to process parameters (gas types, treatment power, treatment time and reactor pressure), the chemical and physical characteristics of a plasma are also influenced by system parameters, such as electrodes (location, coupling mechanism, surface area, materials), reactor (shapes, materials, inertness), 43 Mat. Res. Soc. Symp. Proc. Vol. 414 01996 Materials Research Society

frequency of power supply, gas inlets (position) and vacuum. Subsequently, changes in these parameters may affect the surface chemistry obtained by the plasma modification. Gas In

SProcess Reaction Chamb

0

0 0

0

0

GlowDischarge, (Shortwave and 0Lnwv UV)

--,/

C~~oG

0

"10

Lon O. _0

Subspt.l•

-JGround • RFSor~ce

SPlas-c S....

EJ-1-~d.

•Process (as Out

Figure 1. Schematic diagram of the glow discharge plasma. Generally, the plasma processes can be separated into two major categories based on the gases used in plasmas and their effects on the surface. The first process is called plasma treatment and uses non-polymerizable gases (e.g. oxygen), which can directly modify substrate chemistry and molecular structure. In the second process, called plasma polymerization or plasma deposition, polymerizable gases (monomers or organic precursors) are used in the plasma to form a polymer deposit on the substrate. These two processes are briefly described in the following. Plasma Treatment [11] Plasma treatment can be performed by any reactive gas (all non-inert gases are defined as reactive gases). Oxygen-containing gases, such as C0 2 , 02, water, or mixtures of the gases, are commonly used to create hydroxyl, ether, carbonyl, carboxylic or ester groups; while ammonia is often used to create amine groups [12]. Also, fluorinated gases such as Freon can be used to implant fluorine atoms in some polymers to render them hydrophobic. In a similar way, almost any reactive gas can be used to tailor the surface properties of a polymer. When inert gases are used to treat polymer surfaces, a different type of mechanism is in place [11]. Because the molecules of the plasma gas are reluctant to form bonds with those of the surface, most of the new bonds are formed with donor molecules within the polymer itself. This often results in polymer chain scissions (degradation or etching) and re-splicing along with the formation of c