Monolayers cadmium arachidate

Fig. IV-21. Surface pressure versus area for monolayers of immiscible components a monolayer of pure cadmium arachidate (curve 1) and monolayers of mixed merocyanine dye, MC2, and cadmium arachidate of molar ratio r = 1 10 (curve 2) 1 5 (curve 3), 1 2 (curve 4), and pure MC2 (curve 5). The subphase is 2.5 x 0 M CdC, pH = 5.5 at 20°C. Curve 3a (O) was calculated from curves 1 and 5 using Eq. IV-44. (From Ref. [116].)...

X-ray diffraction has been applied to spread monolayers as reviewed by Dutta [67] and Als-Nielsen et al. [68], The structure of heneicosanoic acid on Cu and Ca containing subphases as a function of pH has been reported [69], as well as a detailed study of the ordered phases of behenic acid [70], along with many other smdies. Langmuir-Blod-gett films have also been studied by x-ray diffraction. Some recent studies include LB film structure just after transfer [71], variations in the structure of cadmium stearate LB films with temperature [72], and characterization of the structure of cadmium arachidate LB films [73], X-ray [74,75] and neutron reflectivity [76,77] data on LB films can be used to model the density profile normal to the interface and to obtain values of layer thickness and roughness. 

The second step, Figure 32b, consists of the covering of the styli with cadmium arachidate LB films. Monolayers of arachidic acid (in principle, it is also possible to use stearic or behenic acids with practically the same results) were spread over the surface of 10 " M CdCli water subphase in a Langmuir trough. The monolayer was compressed to a surface pressure of 27 mN/m and transfered onto styli by a vertical dipping technique. Up to six monolayers were deposited. 

Figure 1. FT-IRRAS double modulation spectrum of six monolayers of Cadmium Arachidate on silver. The inset shows the background water vapor and carbon dioxide present in the measurement. IBM Instruments IR/90 series.

Figure 5. Integrated band areas vs. 1/T for 2 and 6 monolayers of cadmium arachidate on Ag. Comparison of asymmetric (1630 -1490 cm-1) and symmetric (1490 - 1380 cm-1) bands.

Figure 7. 2 L-B monolayers of cadmium arachidate on Ni. P polarization. 4000 spectra co-added. Ratioed to Ni reference mirror. Resolution ca. 10 cm-1 3000 - 2800 cm-1.

Amplified photochemical quenching of carbazolyl fluorescence was observed in mixed LB films containing pure CUA and long-chain fatty adds [49,51], A pure CUA was synthesized from 2-nitrobiphenyl and 11-bromoundecanoic add methyl ester as reported previously [49,50]. Two monolayers of mixtures of CUA (fc= 0.02 - 0.50) and PA were deposited on five monolayers of cadmium arachidate at 15°C and 20 mN m 1 at pH 6.3. 

The samples for the linear Stark effect measurement were prepared as follows. First, 9 monolayers of cadmium arachidate were deposited on fused quartz plates with semitransparent A1 electrodes. Next, test layers which contained 30 layers of compound C180AZ0SN were deposited. Then, further 10 layers of cadmium arachidate were deposited. Finally, the semitransparent top A1 electrodes were vacuum-deposited. 

SAOTS was established to be a true monolayer (rather than a bi- or multilayer) by conductivity and Forster-type energy transfer measurements [183]. Energy transfer experiments were carried out on a composite system which consisted of a mixed OTS and donor cyanine dye (D) monolayer on a glass slide, on top of which a mixed cadmium arachidate acceptor cyanine dye (A) monolayer was deposited (by the LB technique) in such a manner that it covered only half of the glass slide. The other half was covered by a pure... 

Golden et al. studied the grazing-angle spectra of LB and self-assembled arachidate monolayers on aluminum surfaces (32). Rabolt et al. studied cadmium arachidate monolayers on AgBr for transmission, and on Ag for grazing-angle experiments. They found that, independent of the substrate, the chains of the fatty acid salt are oriented within a few degrees of the normal to the surface of the substrate... 

What is the temperature of order-disorder phase transition in LB monolayers of cadmium arachidate Is it reversible ... 

What structure does the LB monolayer of cadmium arachidate have before and after phase transition ... 

One important chemical result from the ESCA studies involves the formation of surface carboxylates. Upon transfer of the monolayer to silver, the formation of a carboxylate could be detected by the production of a single peak in the oxygen Is line due to equivalent oxygens in the carboxylate structure. Since the oxygen spectrum of the monolayer yields near stoichiometric C-0/C==0 ratio of 1, the carboxylate is not detectable. Studies with monolayer films of cadmium arachidate indicated detectability of the carboxylate as a single carbon Is peak. The lack of the formation of this interfacial carboxylate indicates the strength (or weakness) of surface chemistry which occurs on this silver surface as prepared. 

Figure 4.7. These diagrams are designed to emphasize the reproducibility of various physical parameters in monolayer assemblies of different thicknesses a) reciprocal capacitance per unit area versus number of monolayers of cad-mium arachidate on an aluminum substrate (see r erence 38), (Jb) absorption intensity versus number of monolayers for the symmetric carboxylate stretching mode of cadmium arachidate at 1432 cm (see r erence 39), (c) count rate of rays versus number of layers of barium stearate labeled with (see reference 40), and d) X-ray photoelectron signal (XPS) intensity versus number of layers of cadmium dimethylarcwhidate on silver (see reference 28).

Since the two-dimensional packing of the monolayer on the aqueous subphase can differ from that observed after transfer as a LB film to a solid substrate, the molecular packing in the film in the two systems must be known. AFM studies of crystallite formation in LB films have been reported in regard to cadmium-arachidate monolayers. ... 

Chi Jb was purchased from Sigma (St. Louis, MO) and was used without further purification. The photovoltaic cells were prepared by interposing the Langmuir-Blodgett films of Chi b between two dissimilar metal electrodes, i.e. aluminium and silver, with work functions ((()), such that A1 pigment Ag Both metal electrodes were evaporated under vacuum according to the method previously described. The active area of the cell is 0. 5 cm. Before the deposition of Chi b monolayer, the top aluminium electrode was covered with one monolayer of cadmium arachidate transferred at a surface pressure of 30 mN m l. The sandwich cells contained monolayers of Chi transferred on top of the arachidate layer at a surface pressure of 20 mN m l. 

Of course, electrical rectification has been seen in LB multilayer sandwiches [33,34] D-CA I CAjjj I A-CAp of n monolayers of cadmium arachidate doped by donor dyes (D-CAj ), followed by m undoped monolayers CA, followed by p monolayers of cadmium arachidate doped by electron acceptor dyes (A-CAp) (where n+m+p > 7). Photodiode behavior by an LB film of pyrene-a-viologen-a-ferrocene has been seen [35,36]. The interest in detecting rectification by a single D-a-A molecule (by STM), or by an LB film (by either STM or by conventional methods) remains. 

Kuhn and co-workers [39] showed that one can obtain a pn (or DA) rectifier in a LB multilayer sandwich A11 (CA-D)ql(CA)j l(CA-A)j.lAl, where A1 denotes the bulk A1 contacts, (CA-D)q denotes the electron donor system D [q LB monolayers of cadmium arachidate (CA) doped in the ratio 5 1 with suitable organic 7C electron donors D], (CA) denotes a spacer layer of r undoped monolayers of CA, and (CA-A) denotes the electron acceptor system A [s LB monolayers of CA doped with suitable organic K electron acceptors A]. This work was confirmed by Sugi and co-workers [40], who observed rectification properties in LB multilayers, provided that q>3, r>l, and s>3. 

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