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].)...

A unique but widely studied polymeric LB system are the polyglutamates or hairy rod polymers. These polymers have a hydrophilic rod of helical polyglutamate with hydrophobic alkyl side chains. Their rigidity and amphiphilic-ity imparts order (lyotropic and thermotropic) in LB films and they take on a F-type stmcture such as that illustrated in Fig. XV-16 [182]. These LB films are useful for waveguides, photoresists, and chemical sensors. LB films of these polymers are very thermally stable, as was indicated by the lack of interdiffusion up to 414 K shown by neutron reflectivity of alternating hydrogenated and deuterated layers [183]. AFM measurements have shown that these films take on different stmctures if directly deposited onto silicon or onto LB films of cadmium arachidate [184]. 

LB Films of Long-Chain Fatty Acids. LB films of saturated long-chain fatty acids have been studied since the inception of the LB technique. The most stable films of long-chain fatty acids are formed by cadmium arachidate deposited from a buffered CdCl2 subphase. These films, considered to be standards, have been widely used as spacer layers (23) and for examining new analytical techniques. Whereas the chains are tilted - 25° from the surface normal in the arachidic acid, CH2(CH2) gCOOH, films (24), it is nearly perpendicular to the surface in the cadmium arachidate films (25). 

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 photoelectrochemical properties of CdS nanoparticles formed in LB films of cadmium arachidate on ITO glass (indium tin oxide-coated glass) were investigated [188]. The CdS particles were formed by exposure to H2S gas, and then the cadmium arachidate structure was regenerated by exposing the gas-treated films with aqueous solutions of CdCL. Gassing/immersion cycling increased the particle size from 2.3 0.7 nm after one cycle to 9.8 2.4 nm after five cycles. The 9.8-nm particles showed UV-visible ab-... 

FIG. 16 Current versus bias voltage for a CdS nanoparticle on the end of an STM tip. The CdS particles were formed by exposing a bilayer of cadmium arachidate on the STM tip to H2S gas. The other conducting surface is a highly oriented pyrolytic graphite electrode. The inset is a plot of differential conductance versus the bias voltage. (Reproduced with permission from Ref. 202. Copyright 1996 National Academy of Sciences, U. S. A.)... 

In 1988 a method for the formation of CdS particles in Langmuir-Blodged (LB) matrix was suggested (Smotkin et al. 1988). LB film of cadmium arachidate was exposed to an atmosphere of H2S. During the reaction, the head groups of arachidic acid were proto-nated, and CdS was produced according to the following reaction ... 

Scanning tunnel microscopy (STM) was chosen as a tool for realization of this task (Wilkins et al. 1989). CdS nanoparticles were formed in a bilayer of cadmium arachidate deposited onto the surface of freshly cleaved graphite (Erokhin et al. 1995a). The graphite was used as the first electrode. Initially, STM was used for locahzing the position of the particles. Eigure 28 shows the images of different areas of the sample. The particles are vis-... 

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. 

Apart from transistor-like devices, single-electron junctions can also be useful for sensor applications. The simplest one might be the monitoring of H2S. Since the formation of CdS nanogranules takes place when an initial cadmium arachidate layer is exposed to this gas, we can expect the appearance of single-electron conductivity only when it is present in the atmosphere. 

Calibration of the quartz oscillators was performed by consequent deposition of the cadmium arachidate layers (Facci et al. 1993). The dependence of the frequency shift on the number of deposited bilayers is shown in Figure 46. The analysis of the curve reveals a sensitivity of 1.482 pg/mm Hz for our transducer. 

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.

Preliminary results using fixed polarizer FT-IRRAS to study the melting and hydration of cadmium arachidate on low area metals show that both irreversible and reversible conformational changes can be... 

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. 

In addition to the two cases discussed above, images of surfaces coated with other organic adsorbates such as cadmium arachidate Langmuir-Blodgett films, (73), DNA (74), di-methyl and di-2-ethylhexyl phthalate (75), and K-24 liquid crystals (Foster, J.S. Frommer, J.E. Nature, submitted) have been obtained in recent publications. 

Uniform thin films of CdS were prepared by template-assisted electrochemical deposition on Au electrodes covered with Langmuir-Blodgett (LB) films of cadmium arachidate [168]. It was found that different CdS films could be produced depending on the type of LB film used. 

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... 

Langmuir-Blodgett (LB) films prepared from cadmium arachidate LB films formed from dioctadecyldimethylammonium chloride (6) Size-quantized CdS particles formed in situ between the polar headgroups of the LB film Hexamethylphosphate-stabilized, size-quantized CdS... 

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