Plasma deposition, surface modification

Hirotsugu Yasuda is Professor Emeritus of Chemical Engineering and Director of the Center for Surface Science and Plasma Technology, University of Missouri-Columbia. He has over. 300 publications in refereed journals and books and was a pioneer in the exploration of low-pressure plasma for surface modification of materials and deposition of nanofilms as barrier and permselective membranes in the late 1960s. He received the Ph.D. degree in physical and polymer chemistry from the State University of New York, College of Environmental Science and Forestry, Syracuse. 

Figure 2 presents the most common plasma-based surface modification techniques for biomedical applications, described in more detail later plasma assisted chemical vapor deposition or PACVD (RF, MW), physical vapor deposition or PVD (sputtering, cathodic arc), plasma polymerization and grafting, plasma-based thermochemical treatments (e.g. plasma nitriding), ion implantation, plasma immersion ion implantation or PHI, and plasma spraying. Each technique has unique advantages and applications, and the choice of the more adequate technique often depends on the... 

Another issue, which is only briefly mentioned in this Chapter, is the use of cold plasma for surface modification of conventional materials. We can thus improve the properties of "conventional" elements relevant to the construction of electrochemical cells electrode substrates, electrodes themselves, separators, etc. Research interest in this field of the cold plasma technology is comparable to that which is focused on entirely new materials produced by plasma deposition techniques. The use of the plasma treatment technique in... 

Li, Z.F. and Nctravali, A.N. (1992). Surface modification of UHSPE fibers through allylamine plasma deposition. II. effect on fiber and fiber/epoxy interface. J. Appl. Polym. Sci. 44, 319-332. 

Avseenko et al. (2001) immobilized antigens onto aluminum-coated Mylar films by electrospray (ES) deposition. Various surface modifications of the metallized films were studied to determine their abilities to enhance sensitivity. The plastic surfaces were firsf cleaned by plasma discharge treatment, followed by coating with proteins (BSA and casein) or polymers such as poly (methyl methacrylate) or oxidized dextran, or they were exposed to dichlorodimethyl silane to create hydrophobic surfaces. Protein antigen was prepared in 10-fold excess sucrose and sprayed onto the surfaces to form arrays with spot diameters between 7 and 15 pm containing 1 to 4 pg protein. 

The described dual-frequency plasma approach is very versatile and can be applied for deposition, etching, or surface modification merely by changing the operating parameters. This technology can readily be scaled up to large-area industrial requirements. 

Surface modification of a polymer prior to metallization is widely used to improve adhesion. The most common surface modifications employed are electric discharge (corona and plasma) and, more recently, ion-beam treatments QJ- Several mechanisms have been proposed for the improved adhesion after such surface modifications (2). These include mechanical interlocking, the elimination of weak boundary layers, electrostatic attractions, and chemical bonding. All of these can play a role in adhesion depending on the surface modification used, metal/polymer system, type of metal deposition, and the extent of polymer preparation employed. However, for low power, short exposure modifications, the formation of new chemical species which can provide nucleation and chemical bonding sites for subsequent overlayers is considered to be of prime importance (3-51. 

Chemical vapor deposition (CVD) is an atomistic surface modification process where a thin solid coating is deposited on an underlying heated substrate via a chemical reaction from the vapor or gas phase. The occurrence of this chemical reaction is an essential characteristic of the CVD method. The chemical reaction is generally activated thermally by resistance heat, RF, plasma and laser. Furthermore, the effects of the process variables such as temperature, pressure, flow rates, and input concentrations on these reactions must be understood. With proper selection of process parameters, the coating structure/properties such as hardness, toughness, elastic modulus, adhesion, thermal shock resistance and corrosion, wear and oxidation resistance can be controlled or tailored for a variety of applications. The optimum experimental parameters and the level to which... 

In order to elucidate the mechanisms by which a polymeric material deposits and also those by which surface modification of a polymeric material by plasma... 

From the viewpoint of operation of LCVD, pulsed discharge provides effects somewhat similar to those that can be obtained by the remote or secondary plasma operation, namely, (1) reduction of the photoirradiation effect and (2) slowdown of the chemical reaction (surface modification or deposition of material), and allows uniform treatment or deposition. Pulsed discharge always decreases the substrate dangling bonds, which is the measure of the UV irradiation effect, as the value of r increases. Thus, the irradiation damage can be reduced dramatically. On the other hand, the concentration of chemically reactive species also decreases as the value of r increases. 

When plasma polymers of hydrophilic monomers were deposited or the surface of LDPE grafted with hydrophilic poly(acrylic acid), the dielectric breakdown occurred in a very short time. These observations indicate that hydrophilic sites act as the gate for salt intrusion. Since the bulk properties of LDPE are believed to be unchanged with these surface modifications, the quick failure can be interpreted as the consequence of an interfacial phenomenon. The population of the potential salt intrusion sites is a very important factor that ultimately determines the breakdown of the insulation occurring in the presence of salt and electrical stress. 

Parylene N to smooth surface materials has been reported with the application of plasma depositions [13,14]. It was reported that excellent adhesion of Parylene C coating to a cold-rolled steel surface was achieved using plasma polymer coatings, in turn giving rise to corrosion protection of the metal [15]. Another major deficiency of Parylene C is its poor painting properties when paint is applied on a Parylene C film, due to its extremely hydrophobic surface. Because of this, surface modification of Parylene films is necessary to enhance their adhesion performance with spray primers. 

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