Plasma polymerisation

Fabrication of polymers for these small and integrated sensors should be by the new processing technologies, which can produce accurate, mass reproducible and thin polymers. The polymers fabricated by conventional methods may have potential problems such as the difficulty of preparing thin ( 1 pm) and homogeneous films. A plasma-polymerised film offers a new alternative [19]. The plasma-polymerised film is achieved in a glow discharge or plasma in the vapour phase. Such films are thin ( 1 pm), pinhole-free, flat-surface structures and are chemically and mechanically stable. 

In the following sections, the characterisation techniques, properties and applications for both electronical and biological aspects of plasma-polymerised films are described. 

Ultrathin polymer films can be prepared using two kinds of technology. The first includes wet processes like LB, spreading, dipping or solvent casting methods. The other is dry processing, such as physical vapour deposition (PVD) and chemical vapour deposition (CVD). Of these methods, the CVD methods, such as plasma polymerisation, are frequently used to make polymer thin films [24-26]. 

Comparing these two technologies, dry processing is more advantageous, mainly because its technology originated from semiconductor or VLSI processes. VLSI and related 

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H. Yasuda, Plasma Polymerisation, Academic Press, Inc., New York, 1985. 

Grazing angle XAS techniques (XANES) can be applied to ultrathin film systems [316]. Selected NEX-AFS, XPS and FUR spectroscopy results were obtained for plasma-polymerised films with different monomers (styrene, acetylene, ethylene and butadiene) [317]. 

For both types of polymerisation mechanisms, different polymerisation processes can be used ranging from simple bulk and solution polymerisation processes to more sophisticated ones such as suspension, emulsion, interfacial, plasma,... polymerisation processes. 

Yasuda, H.K., Plasma Polymerisation Academic Press New York,... 

M. Shen and A. T. Bell, Plasma Polymerisation, American Chemical Society, Washington, D.C., 1979. 

Lehmann, U., Krusemark, O., Muller, J., Micro machined gas chromatograph based on a plasma polymerised stationary phase. Micro Total Analysis Systems, Proceedings of the 4th pTAS Symposium, Enschede, Netherlands, May 14-18, 2000, 167-170. 

Fig. 40 Conducting film, plasma polymerised from 2-iodothiophene, on silicon. Left topography contrast (shaded pseudo-3D-image) with 405 nm corrugation. Middle real part (conductivity), with a contrast of 2.8 nA. Right imaginary part (capacity), with a contrast of 270 pA, the a.c. currents shown in the middle and in the right image were simultaneously measured together with the topography. The cantilever is made of silicon nitride coated with gold. The excitation is 0.8 V at 60 kHz, the scan speed is 4.17 pm/s...

Techniques for plasma polymerisation have been progressed significantly in recent years [101] and direct formation of fluorocarbon coatings on surfaces, including textiles, holds much promise. 

Plasma Polymerisation Improved Mechanistic Understanding of Deposition, New Materials and Applications... 

A number of authors describe significant improvements in the polymer coating quality obtained by pulsed plasma polymerisation cf. CW). If these claims are substantiated, it would seem likely that research effort will focus increasingly on this mode of plasma deposition. The question arises as to whether the pulsed environment is simply an extrapolation of the low power CW environment, or whether it represents an entirely different plasma environment altogether. 

Plaisma polymerisation is an effective route to new surface chemistries. Plasma polymerisation is widely employed as a coating technology, whereby the value of a commodity material is substantially enhanced by the provision of a specific (new) surface property. By employing low plasma powers, highly functionalised surfaces can be fabricated. Such surfaces may be used to direct specific surface processes, e.g. cell adhesion. 

R. J. Ward, Ph.D. Thesis, An Investigation of the Plasma Polymerisation of Organic Compounds and its Relationship with Surface Photopolymerisation University of Durham, UK, 1989. 

Plasma Polymerisation Impro ed Mechanistic Understanding of Deposition 133... 

Inagaki, N. Plasma Surface Modification and Plasma Polymerisation. Technomic Publishing, Basel, 1996 (ISBN 1-56676-377-1). 

Reproducibility problems in the production of polymer layers as described above can sometimes occur. Since washing steps and drying procedures are often incorporated to remove loosely bound material, and changes in intensity or duration of these steps can result in different layers. Thus the amoimt of the immobilised protein will be different and reduce the reproducibility of the sensors response. The use of thick organic films produced by this method can also lead to frequency instabihty and loss of sensitivity. It is also difficult to control film thickness and homogeneity, which also effect the reproducibility of the surface produced. Weak adhesion between the polymer and the substrate can also be a problem. Methods, such as plasma polymerisation and electropolymerisation, have been developed to overcome these problems and to gain more control over the layer parameters. 

Electropolymerisation of layers again offers control over the growth and thickness of the film. Production of the layer is also quite simplistic. The gold surface is placed in a solution containing the polymer, which is electropoly-merised onto the surface at the appropriate potential for the desired time. After this a very stable highly branched structure is formed on the surface that can be further modified to immobihse the antibodies. As with plasma polymerised methods many crystals can be easily prepared at a time. 

In the grafting from approach, a surface, that was previously activated e.g. by plasma treatment, is exposed to a monomer solution (Huang et al. 2003). A more simple, one-step procedure is to inadiate a polymeric surface like TCP, which is covered with the monomer solution, by an electron beam (Yamada et al. 1990). Alternatively, ultraviolet light and a photosensitiser can be utilised to initiate polymerisation and cross-linking (Curti et al. 2005). A completely different route to prepare thin SRP coatings with good adhesion to solid substrates is plasma polymerisation (Biederman and Osada 1992). In this case, NIPAAm is used as a precursor in a plasmachemical thin film deposition process (Cheng et al. 2005 Pan et al. 2001). 

An unfortunately unsolved problem in plasma polymerisation is the discovery of the exact reaction mechanism. Often, even the type of the predominant active spe-... 

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