LB deposition process

The fabrication of size-quantized semiconductor and metal nanoparticles has attracted a lot of attention (21-23) because of their novel optical and electrical properties and their appealing features as models for basic science. The LB deposition process originally developed for amphiphiles can also be extended... 

Figure 3.4 The LB deposition process showing how the monolayer can be repeatedly transferred onto a solid substrate to form multilayer assemblies.

In the Z-type deposition film, however, the long spacing of 7.2 nm did not agree with the predicted value of 3.9 nm rather, it was the same value as that of the Y-type deposition film. This result demonstrates that the Z-type film does not possess the Z-type layer structure but the Y-type layer structure. It should be assumed that the molecules were turned over in the deposition process and formed the Y-type layer structure, since the Z-type layer structure in which a hydrophilic group touches on a hydrophobic group is unstable. The conclusion from the examination of long spacings well supports molecular orientations in the LB films determined from the linear Stark effect measurements. From the linear Stark effect and the X-ray diffraction measurements, it is demonstrated that the hetero Y-type deposition method is useful for fabrication of stable noncentrosymmetric LB films. 

This trough allow the convenient and efficient preparation of noncentrosymmetric LB films. For the preparation of alternating LB films (hetero Y-type films), two different monolayers are spread on each compartment. After one monolayer is deposited on a substrate in down stroke, the substrate is transferred to the other compartment through the flexible gates. Then, another monolayer is deposited by withdrawing the substrate. One can obtain alternating LB films by repeating the deposition process. For the X-type or Z-type films, a monolayer is spread on one compartment and the other compartment is kept empty. The monolayers are deposited on substrate only in up or down stroke. 

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 film has noticeable planar conductivity, which depends on the number of monolayers as shown in Figure 7.2. The conductivity ofthe film is detectable for two monolayers, but the value is small for very thin films (two to six monolayers). From six monolayers the conductivity begins to increase linearly with the number of monolayers, a feature that is also found in LB films made of charge-transfer salts, and is perhaps a function of the imperfection in continuity of the first monolayers on the metal electrode-quartz substratum boundary. This imperfection came about during the deposition process as a result of different hydrophilic properties of metal and quartz surfaces. 

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