Preparation Oriented Films

Figure 4. Schematic representation of apparatus for preparing oriented films of reduced clays. (Reproduced with permission from Ref. 9. Copyright 1984 The Clay Minerals Society.)...

The driving force for crystallization (AG ) is thus a key thermodynamic variable associated with the transformation process, as is the surface energy. This latter factor has been explored in reasonable depth in other approaches to the problem, " and in some instances this property is believed to dictate the ability to prepare oriented films by CSD. Other investigators have discussed the impact of electrode reaction layers or decomposition pathways. " " ... 

A complete review of the reported properties of ferroelectric thin films prepared by CSD is beyond the scope of this chapter. Suffice it to say that fabrication approaches from each of the three CSD categories noted above have been used to prepare high-quality films in a range of thicknesses. The dielectric response and ferroelectric hysteresis behavior have been widely reported and the reader is referred to References 12 and 13 for representative results. Despite space limitations, three aspects of CSD processing and film properties warrant consideration here. These are (i) the ability to prepare oriented films by CSD (ii) typical stress levels within the films and (iii) the general dielectric properties of the thin film materials compared to the corresponding bulk materials. 

Orientation effects result from the fact that radiation is a transverse vibration and only interacts with the components of dipole moment changing in a direction normal to the beam direction. For example, if a benzene ring compound is oriented with the ring coplanar with the salt plate, out-of-plane vibrational bands will be weakened and in-plane bands will be strengthened relative to an unoriented preparation. Oriented films are prepared deliberately to observe just such effects for vibrational analysis studies but for qualitative and quantitative analysis orientation is not desirable. 

After two days ageing at room temperature, the clear supernatant was eliminated and the remaining suspension was dyalized six times with 0.3 1 distilled water per gram of clay. After a further seven days ageing, the clear supernatant of the dyalized suspension was again eliminated and a part of the remaining suspension was used to prepare oriented films for XRD while the rest was finally lyophilized to obtain powder samples. 

Another recently discovered form of epitaxy is graphoepitaxy (Geis et al. 1979). Here a non-crystalline substrate (often the heat-resistant polymer polyi-mide, with or without a very thin metallic coating) is scored with grooves or pyramidal depressions the crystalline film deposited on such a substrate can have a sharp texture induced by the geometrical patterns. More recently, this has been tried out as an inexpensive way (because there is no need for a monocrystalline substrate) of preparing oriented ZnS films for electroluminescent devices (Kanata et al. 1988). 

Materials PP fabric prepared from highly oriented film-slit fibers. 

Figure 21 shows three possible routes to obtain oriented PAV films by the LB technique. In these route, it is anticipated that orientational orderliness of precursor polymers is introduced in the precursor LB films through the formation of two-dimensionally oriented monolayer of a polyelectrolyte precursor-anionic amphiphile polyion complex at the air/subphase interface and orientation of the precursor monolayers along the dipping direction dining the deposition process. As a result, it is expected to obtain oriented PAV LB films with well-developed jt-coryugation system. In this study, we successfully prepared oriented PAV films using two routes of them, b-1 and b-2 route [35-37]. The chemical structures of PAVs, their polyelectrolyte precursors and an anionic amphiphile used in this study are shown in Fig.22. 

The nanostructured thin-film electrode was first developed at 3M Company by Debe et al. [40] and Debe [41], who prepared thin films of oriented crystalline organic whiskers on which Ft had been deposited. The film was then transferred to the membrane surface using a decal method, and a nanostructured thin-film catalyst-coated membrane was formed as shown in Figure 2.10. Interestingly, both the nanostructured thin-film (NSTF) catalyst and the CL are nonconventional. The latter contains no carbon or additional ionomer and is 20-30 times thinner than the conventional dispersed Pt/ carbon-based CL. In addition, the CL was more durable than conventional CCMs made from Pt/C and Nation ionomer [40]. 

The self condensation of esters of long-chain a-amino acids (methyl 2-aminoocta-decanoate (39), docosanyl 2-aminooctadecanoate (40), methyl 2-aminohexacosanoate (41), docosanyl 2-aminohexacosanoate (42) is used to prepare oriented polypeptide films, which are models for biological membranes.52 ... 

The same metal alkoxide precursor solutions in EtOH and methoxyetha-nol, which were used for preparation ofpowders were also suggested for application of LiNb03 and NaNb03 films on Pt and quartz substrates [524, 1778]. The choice of solution concentration and thickness ofthe layer, which undergoes calcination, is very important for the preparation of films without cracks or bubbles. Oriented LiNbxTa,.x03 (0 < x < 1) films were obtained on the... 

Since many of the aromatic polymers studied [e.g., poly(n-hexylphenylsilane)] are also quite rigid in solution and optical microscopy studies on concentrated solutions often show signs of long range order, a partially oriented sample of this material was prepared by shear flow extension. Third harmonic measurements at 1.064 /im on partially oriented films prepared in this... 

Another oriented film made from sample A was prepared by the same procedure as for sample B, except that sample A was pretreated with hydrazine hydrate. The viscosity was [n] = 0.50 dl/g in 0.5N NaOH (sample C, oriented film). 

Small angle x-ray scattering of the oriented films (samples B and C) showed a discrete interference along the fiber axis corresponding to a long period of 14.0 nm (Figure 3). The stretched film of sample D prepared with the same regeneration procedure used for sample B showed no orientation. This would be... 

In this work the results for two kinds of samples are surveyed. The first type of sample is thin c-axis oriented films with a thickness of about several hundred nanometers [18]. The residual resistance is about several tens of /xQ cm with the residual resistance ratio (RRR) of 2.2 pointing out that films have a disorder between crystallites. This does not preclude the fact that, on some spots, the films contain clean, small, single crystals on which we occasionally may fabricate a point contact (PC). Normally, the contacts were prepared by touching the film surface with a noble metal counter electrode (Cu, Au, Ag) in the direction perpendicular to the substrate. Thus, nominally, the preferential current direction in the PC is along the c axis. Nevertheless, since the surface of the films contains terraces with small crystallites, a PC to the ab plane of these crystallites is also possible. 

Beeck, Smith, and Wheeler 298) prepared nonoriented and oriented nickel films, the latter showing (110) planes parallel to the substrate on which they were condensed. They showed that the catalytic hydrogenation of ethylene at 0°C. proceeds five times more quickly on these oriented films than on randomly oriented films. The heats of chemisorption of... 

There are materials, for example in the form of certain specially prepared polymer films, which, for light incident normal to the film, absorb to an extent dependent on the inclination of the plane of polarization to a unique axis in the plane of the film. Devices made from such films are termed polarizers approximately 60% of the incident unpolarized light is absorbed, and that part transmitted is plane polarized. The E vectors for the transmitted light are perpendicular to the high-absorbance direction. If the incident light is plane polarized, the intensity transmitted depends on the orientation of the polarizer axis with respect to the plane of polarization of the light. A device used in this mode is usually referred to as an analyser . 

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