Cadmium Stearate Langmuir-Blodgett Films Research Articles

A Low Temperature Phase Transition in Langmuir-Blodgett Films

The influences of temperature on the SFG spectra of Langmuir-Blodgett films of cadmium stearate, ferric stearate, stearic acid and octadecanamide are reported. Upon cooling, all films display reversible discontinuous shifts of approximately 8 cm (-1) in the r+, r- and rfermi modes of the terminal methyl groups at approximately 150 K. Reversible changes in the relative intensities of these methyl group peaks, most pronounced in the PPP spectra, are also observed and attributed to a change in the environment of the methyl group that accompanies a discontinuous transition in the ordering of their alkyl chains. The onset of new spectral features at higher frequency is attributed to the observation of ordered water molecules contained within the films. The correlation between the onset of the water features and the onset of the reversible, discontinuous, spectroscopic changes of the amphiphiles argues for a causal connection between the two. In addition to the discontinuous behavior upon cooling, monolayer films of stearic acid and octadecanamide display activity of methylene modes upon exposure to vacuum. Films displaying SFG-active methylene groups at room temperature had them gradually become completely SFG-inactive by 100 K. Heating the films to room temperature revealed that the methylene group activity was reversible. Monolayer films of cadmium stearate and ferric stearate do not display this methylene activity upon exposure to vacuum, suggesting that this behavior may be linked to solvation of the amphiphile's headgroup. These observations suggest that water plays a key role in the stability and structure of LB supported monolayers, and have important implications to those interested in low temperature (cryogenic) effects of biological systems.

Spectro-ellipsometry on cadmium stearate Langmuir–Blodgett films

We have studied cadmium stearate Langmuir–Blodgett (LB) films by spectroscopic ellipsometry (SE) and we have compared the results with those obtained by using X-ray reflectivity and atomic force microscopy. The measurements on cadmium stearate LB films deposited on silicon wafers capped by a native oxide layer provide sound results for films formed by 1–25 molecular layers. The experimental data are well fitted by a Cauchy-type model over the whole examined wavelength range (245–725 nm). The model, which takes into account the anisotropy of the film, uses the film thickness of several mono- and multi-layers films, together with the in-plane and the out-of-plane components of the refraction index as free parameters. The obtained mean thickness of the monolayer (ML), 2.50±0.02 nm, very well agrees with X-rays reflectivity measurements and with literature data.

Surface potentials of polyaniline lb films

Abstract The surface potential (VLB) of Langmuir-Blodgett (LB) films of pure emeraldine base polyaniline (PANi) and mixtures of PANi and cadmium stearate (CdSt) was investigated. Protonated PANi LB films produced from acidic subphases displayed higher VLB than the nonprotonated films transferred from moaolayers spread on pure water. For the mixed LB films, vlb increased with the amount of PANi, and it was always positive regardless of whether an odd or even number of layers were deposited, in contrast to the switch-over from positive to negative potential when going from an odd to an even number of layers for pure cadmium stearate LB films. The results have been analyzed by taking account of the negative contribution from the substrate/film interface.

Langmuir-Blodgett films containing carotenoid dye. II. Structure and conducting characteristics of ethyl ?-apo-8-carotenoate/cadmium stearate LB films

The structure, doping, and electrical conductivity characteristics of ethyl β-apo-8-carotenoate dye (EA8C )/cadmium stearate Langmuir-Blodgett ( LB ) films were investigated. The EA8C/cadmium stearate mixed multilayer thin films, with the molar ratio of 1: 4, prepared at subphase pH 6, exhibited well-defined layered structures as determined by X-ray diffraction (XRD) spectra. The mixed LB films went ready doping upon exposure to iodine vapor or dipping in sulfuric acid solution. The UV/VIS and XRD data showed that the incorporated EA8C was thermally stable up to 80°C. The best conductivity characteristics were obtained with the iodine vapor. Thus, the mixed LB films exposed to iodine vapor showed in-plane and transverse conductivities of 10 -6 and 10 -7 -l0 -8 S/cm, respectively.

A surface Acoutic Wave Study of the Structural Properties of Langmuir-Blodgett Films

We have investigated the propagation of surface acoustic waves in ultrathin ordered organic films. For this purpose cadmium stearate Langmuir-Blodgett films were deposited on YZ LiNbO 3 crystals. By measuring the wave attenuation, changes in the configuration of the film could be detected. The results are explained qualitatively within a microscopic model

Optical properties of Langmuir–Blodgett films investigated by a photoacoustic technique

A photoacoustic (PA) technique based on a four-layer prism configuration has been developed for nondestructive determination of the optical properties of Langmuir-Blodgett (LB) films, in which the PA signal amplitudes are measured as functions of the incident angle of light. With this technique the experimental PA angular spectra of manganese stearate and cadmium stearate LB films were obtained. Based on the electromagnetic theory and taking into account the anisotropic properties of LB films, as well as use of the numerical optimization method, we have simultaneously determined the optical constants and thicknesses of films based on experimental PA angular spectra.

Photoacoustic plasmon resonance spectra of Langmuir-Blodgett films

The surface plasmon spectra of Langmuir-Blodgett (LB) films have been investigated by combining photoacoustic technique with resonant attenuated total reflection spectroscopy. By this technique, the experimental PA angular spectra of cadmium stearate LB films have been obtained. According to the electromagnetic theory and considering the anisotropic properties of LB films, as well as based on the experimental photoacoustic plasma resonance curves, we have determined the optical constants and thicknesses of the films by using numerical optimization method.

Conducting defects in Langmuir-Blodgett films of cadmium stearate

Abstract Langmuir-Blodgett films of cadmium stearate were prepared by the vertical dipping method, and conducting defects were observed by the copper decoration technique. The density of conducting defects was low for the films transferred at surface pressures less than 10 mN m −1 , and it increases with surface pressure, especially at more than 30 mN m −1 . Surface pressure-area isotherms were measured in a Langmuir trough. At the intermediate stage of compression of a Langmuir film, the surface pressure was kept at a certain value for 40 min. An appreciable decrease in the area was observed during the period of constant pressure. The apparent decrement in the molecular area increases gradually with pressure in the low pressure range, but it increases sharply with pressure above 30 mN m −1 . It is considered that the Langmuir film collapses partially at high surface pressures, and conducting defects are produced when the collapse of the Langmuir film is brought about.

特集 超薄膜の構造と機能 ＬＢ薄膜の配向構造と機能

In recent years, much attention has been devoted to Langmuir-Blodgett (LB) films consisting of organized molecular assemblies in the form of ultrathin layers. Concomitantly, there has been an in-creased need for establishment of characterization methods of LB film structures. Among the various analytical methods applicable to thin organic films, Fourier transform infrared (FT-IR) spectroscopy provides the most powerful tool for the analysis of constituent groups in molecules. Recently, we proposed a new method for quantitative evaluation of-the molecular orientation by combining FT-IR reflection-absorption (RA) and transmission techniques, and applied it to the study of LB films of cadmium stearate, azobenzene-containing long-chain fatty acids and their barium salts, and polyion complexes. Here, I outline this method and results obtained for LB films of Cm H 2m-1, -φ-N=N-φ- (CH2) n-COOH (m=8 or 12, n=3 or 5) and their barium salts. Furthermore, I discuss about relationship between the molecular orientation evaluated by the above method and pyroelectricity in alternating (noncentrosymmetric) Y-type LB films consisting of a phenylpyrazine-containing long-chain fatty acid and perdeuterated stearic acid as well as of their barium salts. Finally, I describe new FT-IR reflection techniques such as metal overlayer attenuated total reflection (ATR) method for improving the sensitivity of spectral measurements and external reflection method for thin organic films extended on nonmetalic substrates with the absorption coefficients less than unity.

Measurement of contact angle relaxation during the deposition of Langmuir-Blodgett films of cadmium stearate and valinomycin

We studied the contact angle relaxation during the Langmuir-Blodgett deposition of cadmium stearate and valinomycin films. For cadmium, we found that the relaxation time of the receding contact angle depends strongly on the deposition type; the static value that the receding angle relaxes to depends on the concentration of Cd 2+ ions in the subphase. For 4.0 × 10 -2 M Cd 2+ subphase, the deposition begins and remains Y-type. However, at a lower concentration of 2.5 × 10 -3 M the deposition changes from Y- to X-type. Prior to this transition, the static receding angles for the two different Cd 2+ concentrations are different but the relaxation times are about the same. After the transition, the relaxation process is more than 20 times faster. For valinomycin, the deposition is predominantly Z-type.

Characterization of Langmuir-Blodgett films of cadmium stearate by penning ionization electron spectroscopy

The characterization of cadmium stearate films prepared on silicon substrates by the conventional Langmuir-Blodgett method (for 1 layer) and those by the horizontal lifting (HL) method (for 2–4 layers) was carried out by means of Penning ionization electron spectroscopy and UV photoelectron spectroscopy. The analysis of the relative band intensities of the Penning spectrum indicates that the hydrocarbon end of the stearate ion is exposed outside the surface for all the films studied. The combination of this result and those of an X-ray diffraction study suggests that the films prepared by the HL method have a Y-type structure. The structural changes in the film due to increases in film thickness and to thermal annealing were also studied by Penning ionization and photoelectron spectroscopies.

Thermal disordering of langmuir-blodgett films of cadmium stearate on sapphire

The phase behavior of monolayer and multilayer Langmuir-Blodgett films of cadmium stearate on sapphire is studied using pulsed optoacoustic spectroscopy of the methyl and methylene stretching modes. Heating irreversibly disorders monolayer films but multilayers reach a stable configuration which undergoes reversible phase transitions.

Langmuir-Blodgett film metal/insulator/ semiconductor structures on narrow band gap semiconductors

Langmuir-Blodgett films of cadmium stearate and a substituted diacetylene monomer have been successfully deposited onto the surfaces of the narrow band gap semiconductors InSb and (Hg-Cd)Te. Admittance data for the resulting metal/insulator/semiconductor diodes are presented. The capacitance versus voltage results display the accumulation, depletion and inversion regions typical of an ideal device. The conductance for both devices shows a distinct peak in the depletion region which is thought to be due to losses at interface states. The organic layers are also shown to be transparent to far-IR radiation, indicating that useful detection devices could be based on Langmuir-Blodgett film/narrow band gap semiconductor structures.