Ω-tricosenoic Acid Research Articles

Scanning surface potential microscopic studies of photo-voltaic Langmuir–Blodgett assemblies containing an A–S–D triad molecule

Scanning surface potential microscopy was applied to detect the photo-voltaic response of Langmuir–Blodgett (LB) monolayer assemblies containing an amphiphilic A–S–D triad molecule (ASD) with two different concentrations. The triad acts as a charge separation unit in the same way as the photosynthetic reaction center. In addition, the photo-induced multistep electron transfer systems can be organized in the LB monolayers: first electrons and holes are separated across the monolayer through the ASD triads upon photo-excitation and then the resultant electrons and holes are further separated by lateral diffusion among the concentrated A and the D moieties, respectively. The change in surface potential was clearly observed on an LB assembly with the high ASD concentration in a mixed ASD monolayer with ω-tricosenoic acid (T) (the molar ratio of ASD:T=1:5), while the photo-response could not be observed on an LB monolayer with the low ASD concentration (the molar ratio of ASD:T=1:30). It was interesting to note that the average surface concentration of ASD in the latter diluted monolayer was decreased only to 1 6 of that of the former concentrated monolayer. If the photo-response depended linearly on the ASD concentration, the surface potential would be readily detected in the latter monolayer. The nonlinearity can be attributed to the effect of succeeding lateral diffusion of the separated charges among the ASD triads. To clarify the effect of the lateral diffusion, the other type of LB assemblies, i.e., A/A–S–D double layers, was fabricated by alternate deposition of an additional acceptor (A) layer and the ASD layer. In the A/A–S–D assemblies, significant photo-induced surface potential change was observed with an A layer of a high A concentration (A:T=1:2) even when the ASD concentration was low in the ASD layer (ASD:T=1:30). This result supported an idea that the additional A layer enhanced lateral electron diffusion and resulted in electron accumulation in A layer and hole accumulation in the diluted ASD layer in the A/A–S–D system.

Organo-metallic interfaces studied by positronannihilation spectroscopy

The physical and electronic structures of simple Langmuir-Blodgettfilms (ω-tricosenoic acid and 12-8 diacetylene) and thefilm/substrate interfaces have been investigated by Dopplerbroadening spectroscopy of annihilation radiation and positroniumformation spectroscopy, following implantation of monoenergeticpositrons in the energy range 0.02-30 keV. The annihilationparameters are sensitive to the insertion of the diacetylene groupinto an otherwise very similar film, and to polymerization of thefilm, but not to the presence of cadmium ions in the bulk films.The results suggest the presence of an interface state at whichpositrons annihilate lower-than-average-momentum electrons; one maycautiously conclude from results for monolayer films that thepositron response to this state may be determined by the presence ofcadmium ions as well as the nature of the substrate.

Dynamics of Spontaneous Spreading on Energetically Adjustable Surfaces in a Partial Wetting Regime

Using molecular-kinetic theory, the effects of the substrate surface energy on the time relaxation of the contact angle of squalane droplets are investigated. The studied surfaces are mixed Langmuir−Blodgett films composed of two kinds of molecules of equivalent length but with different end groups: n-tricosanoic and ω-tricosenoic acids. The two-dimensional miscibility of these chemical compounds over the complete range of relative concentration is discussed on the basis of various criteria. We show that the critical surface tension and the friction coefficient of the squalane molecules on these surfaces, calculated from the relaxation of the contact angle, are linear functions of the relative concentration of the ω-tricosenoic acid in the monolayers.

AFM microlithography of a thin chromium film covered with a thin resist Langmuir-Blodgett (LB) film

We demonstrate here the microlithography of a thin chromium film on a quartz plate by using an atomic force microscope (AFM). Langmuir-Blodgett (LB) films of ω-tricosenoic acid were examined as resist films. By scanning an AFM tip under a high normal force, the ω-tricosenoic acid LB film deposited on the chromium film was scratched out. By the further use of wet etching of the chromium film, the process of submicrometer-scale lithography was demonstrated. Protection of the chromium film against etching by the use of multilayered LB films is discussed in terms of the probability of formation of tunnel defects entirely across the LB film.

Medium energy ion beam analysis and modification of Langmuir-Blodgett thin films

The erosion behavior of cadmium arachidate Langmuir-Blodgett films is studied under 270 keV He and Ar ion irradiation. Initial characterization by medium energy time-of-flight backscattering yields a thickness and stoichiometry consistent with an unmodified film. In addition, time-of-flight elastic recoil detection is used to monitor the hydrogen evolution from the films as a function of the cumulative dose. After a dose of 5 × 10 14 Ar ions/cm 2, the film is reduced to less than 50% of its initial thickness and depleted in hydrogen. Smaller losses are measured for He at a dose of nearly 1 × 10 15 ions/cm 2. Dramatic changes are observed in the interference color of 50-layer films under ion erosion. Measurements by ellipsometry yield thicknesses which are consistent with the backscattering estimates and indicate an increase in the refractive index of the film. The response of cadmium arachidate to energetic ions is compared with the cadmium salt of ω-tricosenoic acid, which can polymerize due to the presence of a CC double bond.

Electrical manifestation of dielectric non-centrosymmetry using Langmuir-Blodgett multilayers of ω-tricosenoic acid

Centrosymmetric (Y-type) and non-centrosymmetric (Z-type) Langmuir-Blodgett (LB) multilayers of ω-tricosenoic acid have been deposited as part of an M¦LB¦M structure and the electrical characteristics measured. The symmetry of the LB film was manifested in the electrical properties of the junction, with the behaviour of centrosymmetric LB films being independent of the applied bias sense and non-centrosymmetric LB films possessing a distinct bias sense dependence.

Nanolithographic patterning of Au films with a scanning tunneling microscope

We present a new lithographic technique with a scannning tunneling microscope (STM), allowing us to pattern thin evaporated Au films at the nanometer scale. The electron beam produced by the STM tip is used to expose a very thin layer of ω-tricosenoic acid. Only four monolayers of the acid, which acts as an electron sensitive, negative resist, are deposited on top of the Au films using the Langmuir–Blodgett technique. We have verified the influence of the exposure conditions on the quality of the fabricated fine-line structures with a linewidth down to 15 nm. We can also measure the electrical properties of narrow Au lines which interconnect large predefined contact pads. As expected, the low-temperature magnetoresistance is strongly influenced by quantum interference effects.

Atomic force microscopy and friction force microscopy of Langmuir–Blodgett films for microlithography

We describe the study of microlithography of a thin chromium film on a quartz plate by an atomic force microscope (AFM) and a friction force microscope (FFM). The scratching of Langmuir–Blodgett (LB) films of ω-tricosenoic acid deposited on the chromium films was carried out by scanning an AFM tip under a high normal force of ∼5×10−8 N. The scratched depth was measured by a topographic AFM image recorded by scanning with a new tip under a low normal force of 1×10−8 N. The surface properties of the scratched surfaces created in the multilayered LB films were studied by the FFM. From (1) the wear patterns observed on the scratched surface of the multilayer and (2) the high resistance against scratching of the single monolayer observed by AFM and FFM, it was concluded that the first monolayer always remained even after scratching under the high normal force. Etching resistance of the chromium surfaces covered with LB films with a various number of monolayers was also studied by measuring elapsed times required for complete etching. A drastic change in the etching resistance was observed between the bare or the single monolayer covered chromium films and the multilayer covered ones.

Nanolithographic patterning of metal films with a scanning tunnelling microscope

We have developed a new technique, which allows to pattern thin evaporated Au films at the nanometer scale with a scanning tunnelling microscope (STM). The STM tip is used to expose a very thin layer of ω-tricosenoic acid, which has been deposited on top of the Au films using the Langmuir-Blodgett technique and acts as an electron sensitive, negative resist. We have fabricated narrow Au lines with a width down to 15nm and we have checked that our STM lithography does not degrade the metallic properties of the Au films. The power of our lithographic patterning technique is nicely illustrated by the fact that we can attach electrical gold contacts to a small bundle (total diameter of 50nm) of carbon nanotubes ("Buckey tubes") and measure the electrical resistance of the bundle as a function of temperature and magnetic field.

Water structure at interfaces studied by total internal reflection Raman spectroscopy

Total internal reflection Raman spectroscopy has been used to study the OH stretching vibrational band of water adjacent to a hydrophobic surface, formed by a Langmuir—Blodgett film of ω-tricosenoic acid. The Raman spectra indicate that the structure of water is enhanced in the neighbourhood of the hydrophobic surface. Various experimental difficulties hinder the assessment of the range of this structural enhancement, but it seems likely to extend over at least several molecular diameters.

Submicrometer lithographic patterning of thin gold films with a scanning tunneling microscope

A scanning tunneling microscope (STM) has been used to locally expose Langmuir–Blodgett layers of a negative electron beam resist (ω-tricosenoic acid) on top of a thin gold film. The STM operates in a dry nitrogen atmosphere at a voltage difference of about −10 V between the electrochemically etched Pt-Ir tip and the gold surface. After development in ethanol, the unexposed areas of the gold film are removed by argon ion milling. Gold wires with a linewidth down to 15 nm have been prepared. Electrical transport measurements confirm the homogeneity and the one-dimensional metallic character at low temperatures of the gold structures.

The measurement of the piezoelectric effect in Langmuir-Blodgett films

Pyroelectric Langmuir-Blodgett (LB) films of 1-docosylamine alternated with ω-tricosenoic acid, and an organo-ruthenium complex alternated with behenic acid have been studied for their piezoelectric effect. A purpose built rig was designed for applying an oscillating bending flexure to the composite structure (comprised of a glass substrate, metal electrode, and active film), producing tensile and compressive stresses in the film on its surface. The piezoelectric d 31 coefficient was determined from the stress state in the active layer, the resultant charge, and the elastic properties of the composite. The accuracy of this experimental method was verified by measuring the piezoelectric response of a thin (1.3 μm) spuncoat, polarized film of a 70:30 VF TrFE copolymer with known piezoelectric and elastic properties. Piezoelectric coefficients of 0.023 pC N −1 and 0.17 pC N −1 have been obtained from the acid/amine and the alternate layer ruthenium complex, respectively. The higher degree of piezoelectric activity in the ruthenium complex is believed to be due to the higher molecular mobility in this material.

Photopolymerization of a ω-tricosenoyl derivative of β-cyclodextrin in Langmuir-Blodgett films

Photopolymerization in the LB films of a newly synthesized ω-tricosenoyl derivative of β-cyclodextrin (vinyl-β-CD) and mixtures with ω-tricosenoic acid have been studied by monitoring the change in IR spectra. Vinyl-β-CD formed a stable monolayer with the closest hexagonal packing of cyclodextrin rings parallel to and long alkyl chains perpendicular to the film plane. The polymerization in the LB films was influenced by the mode of deposition and the composition of the mixtures. It has been found that the intermolecular polymerization of vinyl-β-CD can be promoted through the interposition of ω-tricosenoic acid in the blank space between the hexagonally packed molecules of the cyclodextrin derivative. Solvent resistivity of the LB films containing cyclodextrin with specific functions of the cavity was improved by the polymerization.

Second harmonic generation in mixed carotenoid-fatty acid and carotenoid-cyclodextrin Langmuir-Blodgett films

In this paper we report on the second harmonic generation properties of non-centrosymmetrical Langmuir-Blodgett films built from mixtures of push-pull carotenoids with ω-tricosenoic acid or amphiphilic cyclodextrin. The effects of the carotenoid as well as of the diluent on the orientational order have been studied both in monolayers and alternate active-passive multilayers.

Dye fluorescence kinetics of Langmuir-Blodgett films

In this paper fluorescence decay is applied to investigations of perylene aggregate formation in ω-tricosenoic acid LB films and aggregate of thiacyanine dye in LB films. The complicated decay law of fluorescence of perylene and the extremely short lifetime (approx. 500 ps) of the excited thiacyanine dye in LB films is investigated. The kinetic fluorescence characteristics were measured by a time-correlated single photon technique.

Electrical defect visualization in insulating Langmuir-Blodgett films

Direct observation of conducting defects in Langmuir-Blodgett (LB) films by scanning electron microscopy (SEM) is unsuccessful because of defect size (around 50 nm according to literature). In the present paper, a decoration method is described which consists of a local electrochemical deposition of copper on the defects. This technique allows successful, non-destructive SEM observation of the conducting defects. An experimental technique using backscattered electron imaging and X-ray microanalysis is presented for the elimination of substrate artefacts. Typical micrographs are shown. Comparative studies have been worked out on LB films of various molecules: ω-tricosenoic acid, behenic acid, stearic acid, tetracyanoquinodimethane derivatives, amphiphilic pyridino porphyrazine. Results have been obtained on the density and spatial distribution of the defects showing that, among the tested molecules, ω-tricosenoic acid is the best candidate for insulating purposes. Information is also reported concerning the shape of the defects, and the influence of parameters such as transfer speed and number of layers.

Well organized Langmuir-Blodgett films based on push-pull carotenoids

In this paper we report a structural study of Langmuir-Blodgett (LB) films built from different mixtures of a push-pull carotenoid and ω-tricosenoic acid. Even for low dilution ratios, Langmuir films of the modified carotene diluted by ω-tricosenoic acid exhibit a very good cohesion and the surface per carotenoid molecule is close to 25 Å 2. The mixed films can easily be transferred onto solid substrates whatever the dilution ratio. UV-visible linear dichroism examination of the mixed LB films confirms that the chain-like π-conjugated molecules are oriented perpendicularly to the substrate in card-packed aggregates.

Relationship between structures and polymerizabilitues of ω-tricosenoic acid thin films

Deposition of ω-tricosenoic acid films was tried by the Langmuir-Blodgett (LB) and vacuum deposition (VD) method, and structures and polmerizabilities of the films were investigated for applications to thin resist film. It was shown that the LB and VD films had predominant molecular orientation tilted to the substrate normal, and that the LB films had larger molecular tilt angles than those of the VD films. Moreover, it was proved that the polymerizability of ω-tricosenoic acid film was dependent on the molecular tilt angle.

Supermolecular engineering by the Langmuir-Blodgett method

Molecular electronics as well as controlled surface chemistry require highly organized molecular assemblies with specific properties, similar to those of biounits.The Langmuir-Blodgett (L.B.) method, which allows for deposition of one complete solid monolayer of molecules after another, is a very powerful tool to build up such artificial active machineries at the molecular level in the form of ultrathin films. This supermolecular engineering is based on variants of the L.B. method and on specific features of the chemistry of L.B. films. It gives rise to polymers with specific properties: the polymerization of ω-tricosenoic acid and amphiphilic pyrrole are taken as examples. Recently, the use of a semi-amphiphilic compound instead of amphiphilic molecules in conjunction with these methods has given rise to new materials with original electronic properties: conducting molecular thick films and ultrathin films with cooperative spin transition. These materials are of great interest in the high-technology fields of chemical and biosensors, surface catalysis and nanoelectronics.

A new highly conducting Langmuir-Blodgett film based on a radical ion salt of a tetrathiafulvalene derivative

We have obtained very stable Langmuir films from a (1:1) mixture of a tetrathiafulvalene (TTF) derivative (ethylenedithiodioctadecylthio TTF) with ω-tricosenoic acid, compressed on a pure water subphase at surface pressures up to about 35 mN/m. These films can be transferred by the classical Langmuir-Blodgett method with a constant transfer efficiency close to unity, and films more than 100 layers thick can be built up in this way. After exposure to iodine vapor and subsequent moderate heating at about 40°C, these films become conducting, and their in-plane direct current conductivity reaches a value of about 2 × 10 −1 Ω −1 · cm −1 at room temperature. A preliminary interpretation of this behavior is proposed and strong arguments are brought out in favor of an electronic conduction mechanism arising from a mixed valence state in the TTF derivative array.