Arachidic Acid Langmuir-Blodgett Research Articles

Green and solid state reduction of GO monolayers sandwiched between Arachidic acid LB layers

A novel, single step and environment friendly solid state approach for reduction of graphene oxide (GO) monolayers has been demonstrated, in which, arachidic acid/GO/arachidic acid (AA/GO/AA) sandwich structure obtained by Langmuir-Blodgett (LB) technique was heat treated at moderate temperatures to obtain RGO sheets. Heat treatment of AA/GO/AA sandwich structure at 200 °C results in substantial reduction of GO, with concurrent removal of AA molecules. Such developed RGO sheets possess sp2-C content of ∼69 %, O/C ratio of ∼0.17 and significantly reduced I(D)/I(G) ratio of ∼1.1. Ultraviolet photoelectron spectroscopy (UPS) studies on RGO sheets evidenced significant increase in density of states in immediate vicinity of Fermi level and decrease in work function after reduction. Bottom gated field effect transistors fabricated with isolated RGO sheets displayed charge neutrality point at a positive gate voltage, indicating p-type nature, consistent with UPS and electrostatic force microscopy (EFM) measurement results. The RGO sheets obtained by heat treatment of AA/GO/AA sandwich structure exhibited conductivity in the range of 2–7 S/cm and field effect mobility of 0.03–2 cm2/Vs, which are comparable with values reported for RGO sheets obtained by various chemical/thermal reduction procedures. The extent of GO reduction is determined primarily by proximity of AA molecules and found to be unaltered with either escalation of heat treatment temperature or increase of AA content in sandwich structure. The single-step GO reduction approach demonstrated in this work is an effective way for development of RGO monolayers with high structural quality towards graphene-based electronic device applications.

Advantages of the Biomimetic Nanostructured Films as an Immobilization Method vs. the Carbon Paste Classical Method

Tyrosinase-based biosensors containing a phthalocyanine as electron mediator have been prepared by two different methods. In the first approach, the enzyme and the electron mediator have been immobilized in carbon paste electrodes. In the second method, they have been introduced in an arachidic acid Langmuir-Blodgett nanostructured film that provides a biomimetic environment. The sensing properties of non-nanostructured and nanostructured biosensors towards catechol, catechin and phenol have been analyzed and compared. The enzyme retains the biocatalytic properties in both matrixes. However, the nanostructured biomimetic films show higher values of maximum reaction rates and lowest apparent Michaelis-Menten constants. In both types of sensors, the sensitivity follows the decreasing order catechol > catechin > phenol. The detection limits observed are in the range of 1.8–5.4 μM for Langmuir-Blodgett biosensors and 8.19–8.57 μM for carbon paste biosensors. In summary, it has been demonstrated that the Langmuir-Blodgett films provide a biomimetic environment and nanostructured biosensors show better performances in terms of kinetic, detection limit and stability.

J-Aggregation Characteristics of Merocyanine Dye with Arachidic Acid LB Films by Heat Treatment

For a measurement of J-aggregation characteristics by heat treatment, we fabricated arachidic acid (AA)-Merocyanine dye mixed Langmuir-Blodgett (LB) films. pi-A curves were used to investigate the surface pressure of the LB film from a liquid to a solid state while the pressure ranged from 35 and 40 mN/m. When the surface pressure reached 40 mN/m, a monolayer was deposited onto the hydrophilic glass substrates by Y-type deposition. For the UV spectrum observation, a multi layer film was deposited. A narrowing of the red-shifted band was observed. We studied the effect of heat treatments at temperatures below 60 degrees C by observing the UV spectra of merocyanine dye (MD). The J-aggregation was centered at 550-590 nm at 20 degrees C-25 degrees C. We will study the system before and after the application of heat treatment J-aggregation. The J-aggregation will be thermally induced in the mixed LB films by heat treatments at various temperatures. We expect that after heat treatment, the spectral shape and peak of the band will be altered. We investigated that morphology of MD using STM. Also I-V curve was decreased as increasing temperatures.

Tetrapyrazinoindoloporphyrazine Langmuir-Blodgett films

We fabricated tetra(5-n-nonyl-8-tert-butyl-2,3-pyrazino[2,3-b]indolo)porphyrazinato copper(II) (Cu-Pc-C8) Langmuir-Blodgett (LB) films. We further investigated the influence of arachidic acid (AA) as a transfer promoter, as well as the effect of dipping speed, on the deposition of the films on hydrophilic and hydrophobic substrates. In the case of pure Cu-Pc-C8 LB deposition on a hydrophilic substrate, the transfer ratio was close to one for up-stroke depositions, but the previously deposited film was peeled off and re-spread onto water at down-stroke depositions. Whereas the stability of the Cu-Pc-C8 LB films was not improved by AA addition on hydrophilic substrates, the deposition of Cu-Pc-C8 was significantly improved by the presence of AA on a hydrophobic substrate. The AA-assisted deposition had transfer ratio of close to 1 and was essentially stable up to 10-layer depositions. Comparison of the UV-visible spectrum of a Cu-Pc-C8/AA LB film with that of Cu-Pc-C8/AA solution in dichloroethane revealed that the Soret and Q bands for the Cu-Pc-C8/AA LB film were broadened and red-shifted due to the aggregation of phthalocyanines upon assembly in the LB film.

CdS/ZnS core–shell nanoparticles in arachidic acid LB films

Core–shell CdS/ZnS nanoparticles in arachidic acid film were prepared through a novel Langmuir–Blodgett (LB) approach. Post-deposition treatment of the precursor LB multilayers of cadmium arachidate with H 2S gas followed by intercalation of Zn 2+ ions and further sulfidation result in the formation of CdS/ZnS nanoparticles in the LB film. The formation of these nanoparticles and resulting changes in layered structures were studied by FTIR and X-ray reflection measurements. The optical properties were studied using UV–vis absorption and photoluminescence spectroscopy. A red-shift in the absorption spectrum and enhancement of CdS excitonic emission together with reduction of surface states emission suggest that after the intercalation step, a thin layer of ZnS surrounds the CdS nanoparticles, thus forming a core–shell structure. Subsequent to the second sulfidation, a further red-shift in absorption suggests the formation of a thicker ZnS coating on CdS. Electron diffraction of CdS nanoparticles coated with thicker ZnS showed the diffraction patterns of only ZnS, as expected for core–shell structures.

1114 ナノ薄膜の表面エネルギーに関する研究 : アラキジン酸LB膜を用いた有効分散成分理論の検証(マイクロトライボロジー,一般講演)

Dependences of surface energy on ultrathin solid film thickness were investigated experimentally and theoretically. The arachidic acid Langmuir-Blodgett film on a glass plate was used as an ultrathin film sample. The surface energies as a function of the LB film thickness were experimentally obtained from contact angle measurements. The theoretical equation of the dispersive component of the surface energy of the ultrathin film were derived from the van der Waals pressure equation for a multilayered system. The theoretical values were found to agree with the experimental ones and the theoretical equation presented in this study were considered to be useful for prediction of the surface energy of the ultrathin film on a solid substrate.

Enhancement of ferroelectricity in Langmuir–Blodgett multilayer films of weak-polar organic molecules

Ferroelectricity in Langmuir–Blodgett (LB) films (Z-type and alternated Y-type) of nitrogencrown (NC) and arachidic acid (AA) was investigated by electric polarization measurements and small angle X-ray diffraction (SAXD). For Z-type AA LB multilayer and the AA LB films incorporating barium ions, as well as for Z-type NC LB multilayer and the Y-type NC/AA alternating LB films, hysteresis loops of the samples were observed and confirmed existence of the remnant polarizations in the LB films. Their corresponding remnant polarizations were found to be 15, 180, 450 and 9400 μC m −2, respectively. Therefore, the maximum ratios of remnant polarizations up to 620 (9400/15)-folds were obtained from NC/AA alternating LB films. The enhancement of ferroelectricity in NC/AA alternating LB films was observed for the first time. It was demonstrated that the enhancement of ferroelectricity in the LB films could be created by incorporation of barium ions into the LB film structures and strong interaction due to electron clouds redistribution largely originated from the compact insertion configuration of AA between two chains of NC molecules in interleaving films.

Investigation of ITO surface modified by NPB and arachidic acid LB films

NPB and arachidic acid (AA) are introduced to the ITO surface through Langmuir–Blodgett (LB) technique to modify the hydrophilic surface to hydrophobic surface. The π– A isotherms and AFM images of NPB–arachidic acid with different mol concentration show that they can form stable and condensed LB films, and the compactness are increased with the increasing of the NPB molecular concentration. The surface morphologies of the composite films were investigated by atomic force microscopy (AFM). The surface properties of the film are characterized by contact angle and cyclic voltammetry.

Polyimide 터널 장벽을 이용한 Au/polyimide/유기 단분자막/Pb 구조에서 비탄성 전자 터널링에 관한 연구

Using polyimide Langmuir-Blodgett(LB) films as a tunneling harrier, we fabricated Au/Polyimide/1-layer arachidic acid/Pb structure in order to investigate electron transport properties through a junction. It was found that 9-layer polyimide LB films function as a good tunneling harrier in a study of current-voltage(I-V) chararteristics. And several peaks originating in the vibrational modes of the constituent molecules of 1-layer arachidic acid LB films were clearly observed in d<TEX>$^2$</TEX>V/dI<TEX>$^2$</TEX>- V corves.

Ferroelectricity of weak-polar organic molecules in alternate Langmuir-Blodgett multilayer films

Ferroelectricity in Langmuir-Blodgett (LB) films (Z-type and alternated Y-type) of nitrogencrown (NC) and arachidic acid (AA) was investigated by electric polarization measurements and surface pressure-molecular area π(π-A) isotherm. For Z-type AA LB multilayer and the AA LB films incorporating barium and manganese ions, as well as for Z-type NC LB multilayer and the Y-type NC/AA alternating LB films, typical hysteresis loops of the samples were observed and confirmed existence of the remnant polarizations in the LB films. Their corresponding remnant polarizations were found to be 15, 180, 650, 450 and 9400 μC · m−2, respectively. Therefore, it was demonstrated that the enhancement of ferroelectricity in the LB films could be created by incorporation of barium and manganese ions into the LB film structures and strong interaction between alternating monolayers of the samples. These novel approaches can be employed to create strong ferroelectric LB films to make ferroelectric thin-film device for practical applications.

Structure of CdS–arachidic acid composite LB multilayers

Abstract Langmuir–Blodgett (LB) multilayers of cadmium arachidate were used as precursors to grow semiconducting CdS nanoclusters. The formation of CdS in the multilayers was determined by Fourier transform-infrared (FT-IR), ultraviolet–visible (UV–vis) and Raman spectroscopy. The structural changes occurring as a consequence of CdS formation have been characterized using X-ray reflection (XR) and grazing incidence X-ray diffraction (GIXD) techniques. The CdS containing composite multilayers exhibit the presence of two types of molecular domains, one with close packed herringbone arrangement and the other with tilted molecular chains with no in-plane order. The structural and spectroscopic evidences together suggest that the CdS nanoclusters formed within the arachidic acid LB matrix are quasi two-dimensional in nature with lateral dimension ∼5–10 nm and thickness ∼1.1 nm.

The effect of insulating spacer layers on the electrical properties of polymeric Langmuir-Blodgett film light emitting devices

We report on the use of insulating Langmuir-Blodgett (LB) films to improve the quantum efficiency of light emitting devices based on polymeric LB films. The insertion of arachidic acid layers between a poly-(2-methoxy,5-(2'ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV) film and an aluminium cathode was found to decrease the turn-on voltage for electroluminescence and to double the quantum efficiency. In contrast, depositing the fatty acid layer between the polymer and the indium tin oxide anode produced little change in the device efficiency. Dual-layer structures using MEH-PPV as the light emissive layer and poly-(p-(3-hexyl pyridylene)) as an electron transport layer were also tested. Again, an increase in device efficiency could be obtained by placing arachidic acid LB layers immediately beneath the metallic cathode.

LB films formed from arachidic acid monolayers on an aqueous solution of a ruthenium(II) complex

Up to 91-layer arachidic acid (AA) LB (Langmuir–Blodgett) films containing photofunctional molecules, tris(1,10-phenanthroline) ruthenium(II) chloride hexahydrat (Ru(II)), were deposited by using Ru(II) aqueous solution as a subphase without any other ions. The AA LB films on Ru(II) subphase was characterized by the UV–visible, photo-induced emission spectra and low angle X-ray diffraction. Both absorption and fluorescence spectra have shown that the LB films have good optical properties in visible region. As many as five Bragg's diffraction peaks were observed in the 2 θ angle range of 1 to 10°, indicating that the LB films have good arrangement with the Ru(II) ions on the end of the AA chain homogeneously.

Electro-optical characterizations of the large second-order optical nonlinearity of Langmuir-Blodgett films

The second-order optical nonlinearity of was deduced from the Pockels response of mixed -arachidic acid Langmuir-Blodgett monolayers by using electro-optically modulated attenuated total reflection spectroscopy. We obtained a considerable second-order susceptibility for of (namely ) which is in agreement with that obtained from the measurement of second-harmonic generation and attributed to the electrical quadrupole and/or magnetic dipole contributions of molecules.

Electrical properties of C22-quinolinium(TCNQ) and polyamic acid alkylamine salts Langmuir–Blodgett films

Electrical properties of C22-quinolinium(TCNQ) and polyamic acid alkylamine salts Langmuir–Blodgett (LB) films have been investigated through a study of surface pressure (π)–area (A) isotherms, current–voltage(I–V) characteristics, frequency-dependent dielectric responses, and thermally-stimulated currents (TSC). Through-plane I–V characteristics of C22-quinolinium(TCNQ) LB films show an anomalous behavior of breakdown near the electric-field strength of 106 V/cm. Frequency-dependent dielectric constants of the thermally annealed C22-quinolinium(TCNQ) LB films show that there are two characteristic dispersions in a frequency range of 10–13 Hz; one is a dispersion occurring near 1 MHz coming from the orientational polarization of the molecules and the other is probably due to an interfacial polarization below 1 kHz when the annealing temperature is above 80°C. The annealing temperature-dependent dielectric constants of the C22-quinolinium(TCNQ) LB films show that there are two maximum; one at near 80°C and the other at near 180°C. The first peak seems to be related to a disorder of alkyl chains. In the I–V characteristics of Z-type polyamic acid alkylamine salts (PAAS) LB films measured along the through-plane at room temperature, ohmic conduction has been observed below around 105 V/cm, which is similar to that of C22-quinolinium(TCNQ) LB films. Non-ohmic conduction has been observed above around 105 V/cm and the conduction mechanism can be explained by Schottky effect. Frequency-dependent dielectric responses of the PAAS LB film show that there is a dispersion at 104 Hz when the annealing temperature reaches about 100°C. Measurements of thermally-stimulated currents of those LB films were performed from room temperature to about 250°C and the temperature was increased at a rate of 0.2°C/s linearly. TSC peaks are observed at about 70°C in the arachidic acid LB films, and at about 70 and 160°C in the PAAS LB films. They indicate that the peak at 70°C is resulted from the alkyl group, and the other peak at 160°C is probably due to CO group in PAAS molecules.

Scattered light due to excited surface plasmon in arachidic acid LB ultrathin films on silver thin films

Scattered light due to excited surface plasmon in arachidic acid (C20) Langmuir–Blodgett (LB) ultrathin films on the silver (Ag) thin films was measured to obtain information about surface roughness of the films. The scattered light intensities were assumed to be described by a linear superposition of roughness spectra, and the experimental angular distributions were explained by some pairs of the transverse correlation length σ and the surface corrugation depth δ. The angular spectra strongly depended on the roughness parameters, σ and δ. The roughness parameters for the C20 LB films were decided by fitting the theoretical angular patterns to the experimental results. The angular spectra varied with the number of the C20 LB monolayers on the Ag films. It is suggested that the surface roughness of the C20 LB films changed with the number of monolayers. The scattered light method is useful for evaluating surface roughnesses of LB ultrathin films.

Thermally stimulated currents of Langmuir–Blodgett films

This paper describes thermally stimulated currents (TSCs) of arachidic acid (AA) and polyamic acid alkylamine salts (PAAS) Langmuir–Blodgett (LB) films. The measurements were performed from room temperature to about 250°C and the temperature was increased at a rate of 0.2°C/s linearly. Two peaks are observed at about 70°C and 90°C in the arachidic acid LB films, and at about 70°C and 160°C in the PAAS LB films. They indicate that the peak at 70°C arises from the alkyl group, and the other peak at 160°C in PAAS LB film may be due to the C–O group. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the PAAS and arachidic acid powder were measured and analyzed.

The effect of different metal cation incorporation in arachidic acid Langmuir-Blodgett (LB) monolayer films

In the present communication one monolayer Langmuir-Blodgett (LB) films of cadmium arachidate (CdA), lead arachidate (PbA), calcium arachidate (CaA), zinc arachidate (ZnA) and barium arachidate (BaA) have been investigated using core level loss spectroscopy, electron energy loss spectroscopy (EELS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The core level loss spectra and electron energy loss spectra of all the films were largely similar. This has been attributed to the similarity of the band structure of these films, which depends on the hydrocarbon chains rather than the cation incorporated. The NEXAFS spectra show a large angular dependence for the PbA film and barely any angular dependence for BaA. A possible explanation for this observation has been offered on the basis of electronegativities of the cations.

Ellipsometric studies on uranyl arachidate Langmuir-Blodgett films

In the presence of counterions, the quality of fatty acid monolayers, prepared by the Langmuir-Blodgett (LB) technique is highly influenced by the subphase pH value. In this paper, we present ellipsometric studies on arachidic acid LB films, prepared at different subphase pH values, with uranyl (O U O) 2+ as the counterion. In order to obtain the refractive indices and thickness, independently, the films were prepared as steps with bilayer step size. Refractive index, real and imaginary part, monolayer thickness and surface roughness on a microscopic and macroscopic scale have been determined for three different pH values. The results show that films prepared at a pH value of 4.8 and 4.0 are of good optical quality, whereas those prepared at pH 2.5 are inhomogeneous.

Molecular arrangement characteristics of a pyrrole-containing arachidic acid LB film

The transformation of the molecular arrangement of an arachidic acid (C 20) Langmuir-Blodgett (LB) film was studied with an increase of pyrrole (Py) quantity which we used as guest molecules to the host molecules, C 20. The change of molecular occupation area of a C 20 LB film was estimated by π- A curves, a quartz crystal microbalance method and friction force microscopy (FFM). It was found that a C 20 LB film can contain Py molecules 1.4 times as large as C 20 molecules. The observation by FFM showed the enlargement of the occupation area of C 20 upon addition of Py, however, the molecules of C 20 do not change the internal structure of the film upon compression. The experimental results show that the lattice constant of a C 20 LB film is easy to control by the quantity of Py molecules contained in the LB film.