Plasma Surface Modification - Modifying characteristics of surfaces • Adding coatings
Plasma surface modification is an extremely useful and important tool. Modifying a surface’s characteristics is often a necessary part of the industrial process. Plasma surface modification can alter the traits of a surface on the molecular level. Surface activation can be used to increase a surface’s adhesion potential, for example the ability for paints and glue to adhere to it. Plasma surface modification can also be used to create designated patterns on a surface. This is a process called etching and is widely used in the production of printed circuit boards.
Plasma surface modification can layer surfaces with a coating to protect them or give them different characteristics by introducing monomers into the system. This is especially important for the functionalization or activation of polymer surfaces (e.g. o, polypropylene, teflon, etc.), where the plasma can enhance surface adhesion properties. When high-energy ions or electrons bombard the surface, they remove, for example, carboxyl groups and form hydroxyl groups. This leads to an improved bonding between plastics and other materials. Plasma treatment is also used for the oxidation of plastic surfaces and can not only increase the wettability but also the biocompatibility of polymers.
To begin the plasma surface modification process, first you insert the surface you want to treat into the chamber. A vacuum then empties the chamber of air and creates a very low pressure inside. Then a small quantity of gas is added into the chamber. This gas is usually air, hydrogen, nitrogen, argon, oxygen or a combination of these gasses. The gas inside the chamber is then ionized by an electrical charge creating plasma ions. These ions react with the outer layer of the surface and modify it on the molecular level. Depending on the plasma surface treatment that you want to perform, you can adjust the type of plasma used, the pressure inside the chamber, and how long the surface is treated to adapt your surface to the exact specifications that you need.
Plasma surface science also employs different techniques to analyze and study the surface properties of plasma treated materials, such as polymers, ceramics, metals or glass. Some of the methods used are, X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM) or scanning electron microscopy (SEM). The latter two are mostly used for the characterization of thin films or morphology features. XPS is frequently used to study the chemical composition of the plasma treated surface but also to analyze the bulk properties of the treated material.
The term plasma surface modification encompasses all possible changes on a given surface that plasma can induce. This can be etching, coating, sputtering, patterning, oxidizing or chemical activation. Plasma surface modification usually takes some seconds up to minutes but the effect may last days or even weeks. The surface treatment relies on highly energetic electrons and ions, which hit the surface of the treated material (e. g. polymers, glass, ceramics, etc.). These particles then induce changes in the surface, which lead to oxidation, activation, functionalization, plasma polymerization, cleaning or coating of the surface. The results are then measurable changes in the surface properties like morphology, wettability, biocompatibility, adhesion, formation of functional groups or surface energy.
Hence, the one more interesting thing is that the properties of the surface can be altered or optimized with plasma treatment while the bulk parameters remain unchanged. Since the plasma composition is mainly determined by the working gas(es) and the input power, there is a wide range of possible plasma configurations for plasma surface modification. Due to this large variety there is basically no solid surface that cannot be treated with plasma. This can either be done in a low-pressure environment or at atmospheric pressure.
Most of the plasma sources will be low, rf frequency or microwave discharges. The reason for this is that a significant portion of plasma surface modification processes uses oxygen plasma for surface treatment. Since oxygen plasma causes oxidation of any electrode that comes in direct contact with it, plasma generation with inductively or capacitively coupling should be preferred. Depending on the envisioned application the right choice of systems for plasma treatment is of utmost importance but no matter what the needs are, Thierry Corp. has the right equipment for you!
Surfaces of all materials can be modified to some extent with plasma. However, the choice of working gas(es) will strongly depend on the material.
For example, metal surfaces are often treated with argon plasma for cleaning or sputtering but sometimes oxygen is used as well to create a semiconducting surface of a metal oxide.
Oxygen is also commonly used for treating polymer surfaces, as this can either chemically remove contaminants or activate the surface for further processing.
Plasma treatment of polymers (such as polyethylene or polypropylene) can also lead to branching or crosslinking of molecules on or near the surface. This can improve the mechanical strength of the top layers. In the case of very inert materials, such as Teflon hydrogen plasma is utilized.
Other surfaces may be treated with nitrogen, air or hydrogen-nitrogen mixtures. The goals of such surface treatments is manifold; polymers, for example, are very often plasma treated to improve adhesion.
This is of great importance if the polymer in question should be painted, printed on or glued to another material (e. g. metal or another polymer). In recent years the surface treatment of glass and glass fibers has become a topic of interest. Glass is mostly treated with plasma to obtain a super-hydrophilic surface with a very low contact angle or considerably improve the adhesion properties. Glass fibers, on the other hand, have been shown to exhibit increased mechanical endurance, particularly improved interfacial shear strength after the plasma treatment.
Plasma surface modification systems can be divided into atmospheric and low-pressure plasma systems. Both types have their advantages and disadvantages. Low-pressure systems usually operate in the pressure range of some 10 to several 100 Pascals with typical flows of 10 to several thousand sccm.
The plasma ignition is generally performed with low frequencies, radio frequencies or microwaves. The frequency range is somewhere between 40 kHz and 2.45 GHz for commercially available plasma sources. The frequency choice also has an impact on the plasma surface modification because higher frequencies tend to create more reactive plasma with higher ion and electron densities at a given input power. This leads to lower plasma processing times and, thus, higher throughputs.
The plasma source itself can either be inductively or capacitively coupled and there can be several varieties of plasma treatment: DBD discharges or roll-to-roll systems are just two prominent examples.
The right plasma processing equipment is defined by the type of substrate and the kind of surface modification techniques, which are to be applied. Another important group of candidates for plasma modification are biomaterials. Thin films of biomaterials, such as diamond like carbon or titanium oxide are often plasma treated via ion implantation. For this surface modification technique, ions with very high kinetic energy bombard the substrate surface and implant themselves into the top layer of the material via diffusion. This enhances the physical and chemical properties considerably.
Thierry Corp. offers a broad range of plasma systems for all practical plasma processing related purposes. Plasma surface modification is, thus, no exception.
You want to get hydrophilic surfaces with low contact angles, change the surface energy or functional groups of your substrates or enhance the adhesion properties, wettability and biocompatibility? Thierry Corp. offers a large variety of plasma sources, not only for surface functionalization and activation but also for plasma coating or any other form of plasma treatment.
Our plasma technology solutions can create any type of plasma you need, from argon to oxygen plasma, low-pressure or atmospheric pressure plasma, from plasma jets to DBD discharges. You can treat any material you like: polymers, ceramics, metals or glass. If
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