X-type deposition

Y-type deposition X-type deposition Z-type deposition... 

Once the layer is compressed into a two-dimensional solid, a suitable substrate is repeatedly dipped through the floating layer. For one dipping cycle (down and up) it is possible to deposit two layers (Y-type deposition), one layer on the down-stroke only (X-type deposition) or one layer on the up-stroke only... 

Fig. 9 The multilayer structures formed by (a) X-type deposition and (b) Z-type deposition.

Figure 4.12 Deposition on to a hydrophilic substrate to form Langmuir-Blodgett films. Y-type deposition a monolayer is deposited on the upstroke and downstroke. X-type deposition a monolayer is only deposited on the downstroke. Z-type deposition a monolayer is only deposited on the upstroke...

Deposition techniques of monolayers onto substrates. Y- and Z-type deposition require hydrophilic surfaces, like glass, whereas X-type deposition requires hyi"ophobic substrates. 

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air—water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in situ This polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

Multiayer L-B films can be prepared in both methods, by repeated deposition of monolayer on the substrate, with the molecular direction changing alternatively after each deposition (Y-type), or keeping the same molecule direction in all monolayers (X-type or Z-type). 

Pyrite of the Besshi-type deposits is characterized by high Co content ranging from n x 10 to n x 10 wt% (Itoh and Kanehira, 1967), which is quite a bit higher than that of Kuroko deposits. 

Phthalocyanines (Pc) are attractive materials for their potential functions including the semiconductive behaviours in addition to the thermal and chemical stabilities. In particular, control of orientation of the Pc macrocycles in thin films is expected to provide novel molecular electronic devices. Previously, we have found that copper tetrakis(butoxycarbonyl) Pc is oriented nearly perpendicular to the surface and also the dipping direction in the LB films [46], while octa-alkyl Pc derivatives [H2Pc(R)8, CuPc(R)a R = CnH2n+i. n=7,9,11] take the orientation with Pc macrocycles nearly parallel to the plane of films deposited by the horizontal lifting method to form a non-alternating X-type film [47], as illustrated schematically in... 

Figure 6 compares the electroabsorption spectra of the three type of LB films in the wavelength range that corresponds to the absorption due to the transition moment in the direction of the long molecular axis. The applied field was 3.2 x 10s Vcm1 in each case. In the Y-type deposition film, a small Stark signal is observed nevertheless, the Y-type film is assumed to possess a symmetrical molecular orientation. The reason for this weak signal may be that the fluctuation of molecular orientation across the films induced a small asymmetry in the multilayer structure. 

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. 

The quantity and quality of the deposited monolayer on a solid support is measured by a so-called transfer ratio, tr. This is defined as the ratio between the decrease in monolayer area during a deposition stroke, Al, and the area of the substrate, As. For ideal transfer, the magnitude of tr is equal to 1. Depending on the behavior of the molecule, the solid substrate can be dipped through the film until the desired thickness of the film is achieved. Different kinds of LB multilayers can be produced and/or obtained by successive deposition of monolayers on the same substrate (see Figure 4.11). The most common one is the Y-type multilayer, which is produced when the monolayer deposits on the solid substrate in both up and down directions. When the monolayer deposits only in the up or down direction, the multilayer structure is called either Z-type or X-type. Intermediate structures are sometimes observed for some LB multilayers, and they are often referred to be XY-type multilayers. 

Different film architectures can result upon deposition as depicted in Fig. 3.9(e). Y-type multilayers are the most common and can be prepared on either hydrophilic or hydrophobic substrates, and are typically the most stable due to the strength of the head-head and tail-tail interactions. The X-type and Z-type films, with head-tail interactions, are less common. 

Films may be formed only in downstroke (X-type, Fig. 4b). The deposition speed may affect the deposition mode (16,17). If deposition occurs only when films are formed in upstroke Z-type films result (Fig. 4c). These are cases where the head group is not as hydrophilic, eg, COOCH3 (18), or where the alkyl chain is terminated by a weak polar group, eg, N02 (19). In both cases the interactions between adjacent monolayers are... 

Many organic molecules possess very high nonlinear coefiScients. Therefore, if LB films with the required architecture can be formed, these could form the basis of novel devices. To avoid the symmetry inherent with conventional Y-type deposition, X- and Z-type films have been studied. Some of these films displayed a permanent polarization with a strong component in a direction perpendicular to the substrate. However, films produced in this way, with their dipoles supposedly aligned in a common direction, are invariably of poorer quality than Y-type layers. A possible method of improving the structure is to use electric or magnetic fields to help align the molecules. 

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