Poly film surfaces

Polyesters are eneountered in many forms. They are important as laminating resins, moulding compositions, fibres, films, surface coating resins, rubbers and plasticisers. The common factor in these widely different materials is that they all contain a number of ester linkages in the main chain. (There are also a number of polymers such as poly(vinyl acetate) which contain a number of ester groups in side chains but these are not generally considered within the term polyester resins.)... 

Finally, surface properties of PTFEP were modified photochemically by light-induced grafting of poly(AT,Ar,-dimethylacryl amide) onto the film surface of this material to achieve a remarkable enhancement of its hydrophilicity [513]. 

Apart from modifications in the bulk, also surface modification of PHAs has been reported. Poly(3HB-co-3HV) film surfaces have been subjected to plasma treatments, using various (mixtures of) gases, water or allyl alcohol [112-114]. Compared to the non-treated polymer samples, the wettability of the surface modified poly(3HB-co-3HV) was increased significantly [112-114]. This yielded a material with improved biocompatibility, which is imperative in the development of biomedical devices. 

Cobalt(II) chloride was dissolved in poly(amide acid)/ N,N-dimethylacetamide solutions. Solvent cast films were prepared and subsequently dried and cured in static air, forced air or inert gas ovens with controlled humidity. The resulting structures contain a near surface gradient of cobalt oxide and also residual cobalt(II) chloride dispersed throughout the bul)c of the film. Two properties of these films, surface resistivity and bullc thermal stability, are substantially reduced compared with the nonmodified condensation polyimide films. In an attempt to recover the high thermal stability characteristic of polyimide films but retain the decreased surface resistivity solvent extraction of the thermally imidized films has been pursued. 

Poly crystalline silicon (poly-Si) has been formed by the plasma-enhanced decomposition of dichlorosilane in argon at temperatures above 625 °C, a frequency of 450 kHz, and a total pressure of 27 Pa. Doped films have been deposited by the addition of phosphine to the deposition atmospheres (213). Approximately 1 atom % of chlorine was found in the as-deposited films. Annealing in nitrogen at temperatures above 750 °C caused chlorine to difluse from the film surface, grain growth to occur, and the film resistivity to drop. Such heat treatments were necessary to achieve integrated-circuit-quality films. 

The effect of reactive plasma and its distance form the PE film surface has also been studied in detail [138]. The surface of polyethylene films was modified with various water-soluble polymers [(poly[2-(methacryloy-loxy)ethyl phosphorylcholine] (PMPC), poly[2-(glucosyloxy)ethyl methacrylate] (PGEMA), poly(N-isopropylacrylamide) (PNIPAAm) and poly[N-(2-hy-droxypropyl) methacrylamide] (PHPMA)] using Ar plasma-post polymerisation technique [139]. Here, the reactive sites were generated on the PE surface under the influence of argon plasma. These reactive sites on the surface were then utilised to covalently anchor the functional monomers as shown in Scheme 11. 

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Fig. 4. TEM micrograph of a craze tip in poly(styrene-acrylonitrile) (stained with 0s0.t). The film is tilted so the craze front (normal to the film surface) can be seen in projection. Note the stained wedge of plastically deformed polymer ahead of the crtize tip. Courtesy of Dr. A. M. Donald...

A SEM image of diamond particles is shown in Figure 9.15. Unlike past works, diamond film surfaces were well facetted with (111) and (100) faces, or consisted of cubo-octahedrons. Under certain conditions, either (111) or (100) faces of diamond particles were nearly parallel to the substrate surface. It is of intrigue that the (1 ll)-oriented diamond grains have hexagonal faces, as seen in Figure 9.15, rather than triangles that were seen in Refs. [186, 187]. Thus, both (111)- and (100)-textured diamond films were demonstrated to be synthesized on poly-crystalline Cu foils. 

Fig. 12.9. Electron backscatter diffraction (EBSD) map showing the grain structure of a poly-Si film on glass prepared by the ALILE process (left) and the corresponding inverse pole figure showing the preferential (100) orientation of the poly-Si surface (right). The region used for the definition of the preferential (100) orientation -R(ioo) is indicated by a dashed line (20° tilt with respect to the perfect (100) orientation). The sample was annealed at 425°C for 16 h. Afterwards the Al(+Si) top layer was removed by CMP. The area under investigation was 80 x 80 pm2. Red, green and blue correspond to (100), (110) and (111), respectively, (from [39])...

A high preferential (100) orientation of the poly-Si surface is favorable for subsequent epitaxial growth at low temperatures [41-43]. Due to the preferential (100) orientation, the utilization of the poly-Si films formed by the ALILE process as a template (seed layer) for subsequent epitaxial thickening at low temperatures is quite attractive [44]. 

In addition to the experiments with very thin barrier layers, rather thick barrier layers have also been investigated [51]. The thick barrier layers were formed by thermal oxidation of the Al surface (e.g., for 2h at 560°C). With such a thick barrier layer, an estimated average grain size of above 200 pm was reached. But at the corresponding Ta of 450°C, it took days to form a continuous poly-Si film. The influence of a barrier layer formed by thermal oxidation on the preferential orientation of the poly-Si surface was already described (see Fig. 12.10). 

Local reactions take place, for instance, in unconventional lithography approaches. Here, the surface of a polystyrene-Woc -poly(ter/-butyl acrylate) (PS69o-fr-PtBA12io) block copolymer film comprising reactive ter/-butyl ester moieties at the film surface (skin layer of 8 nm thickness) is locally hydrolyzed by a reactant (trifluoro acetic acid) that is delivered by a soft elastomeric stamp, as shown in Fig. 4.38. Thus, the surface is locally modified to yield poly(acrylic acid), which possess higher friction forces than the unreacted tert-butylester region. 

The stability of the properties of polysilicon films to processing is not ideal. The structure and intrinsic stress of LPCVD-poly films created by different organizations but with the same deposition recipe were different [21]. The properties of LPCVD-poly can differ even on wafers from the same deposition run, due to small temperature fluctuations in the deposition furnace [25]. However, since several LPCVD-poly surface-micromachined sensors are in fact produced in high volumes for the automotive industry (e.g., by Analog Devices, Infineon, and Motorola), these literature data may not represent the current state of the art. 

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