Multilayer Langmuir-Blodgett Films Research Articles

Surfactant micellar induced aggregation control of an anionic fluorescent dye in Langmuir-Blodgett film

This work reports the formation of stable Langmuir monolayer of an anionic water soluble fluorescent dye 5(6)-carboxyfluorescein (abbreviated as CFS) by electrostatic interaction with a cationic monolayer. Formation of non-fluorescent H-dimeric sites of CFS molecules in Langmuir monolayer and Langmuir Blodgett films has been controlled by using cationic surfactant micelles of cetyltrimethylammonium bromide (CTAB). Thus the film can act as efficient fluorescence marker. Langmuir monolayer has been investigated by Surface Pressure versus Area per molecule (π-A) isotherm and in situ Brewster Angle Microscope (BAM) studies. Mono and multilayered Langmuir Blodgett films were characterized by using UV–vis absorption and steady state fluorescence spectroscopy.

Multilayer Langmuir-Blodgett thin films studies for chemical sensors development

This paper presents the study of the development of complex organic materials deposited by the Langmuir Blodgett technique. We have synthetized Langmuir Blodgett multilayers for the recognition of toxic chemicals in the air and / or ultraviolet radiation. The sensitive materials are based on multilayers of stearic acid metal salts combined with nanocarbon and metalloporphyrin structures. We prepared and obtained by the Langmuir Blodgett method films with nano-metric thicknesses combined in different concentrations of metal salts of fatty acids, Nano carbon structures and metalloporphyrins. Further we have characterized and tested the materials obtained for the sensitivity and selectivity of multilayers under the influence of various toxic gases and / or ultraviolet radiation obtaining high results in the field of sensors.

Titania Nanofilms from Titanium Complex-Containing Polymer Langmuir-Blodgett Films.

This paper proposes a method of fabricating low-dimensional TiO2 nanofilms at room temperature under ambient pressure conditions. The titanium-containing polymer complex Ti-p(DDA/acac) was synthesized by reacting an amphiphilic copolymer (p(DDA/acac)) with a titanium complex. Its ultrathin films were prepared using the Langmuir-Blodgett (LB) technique. The monolayer was found to be free from hydrolysis and cross-linking side reactions, even at the air-water interface. The transferred LB films (nanosheets) were oxidized by ultraviolet irradiation at room temperature. The photo-oxidized material has an amorphous and porous structure with subnanometer-scale controllability (0.18 nm per layer). Photocatalytic performance was demonstrated by converting multilayered LB films of Ti-(DDA/acac) and the silicon-containing polymer p(DDA/SQ) into ultrathin hetero-multilayers of TiO2 and SiO2 under UV-O3 treatment. The scalability affords a uniform photopattern formation of photo-oxidized TiO2 films over several hundreds of micrometers.

A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants.

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [ZnII (LN2O2 )H2 O] (1) and [GaIII (LN2O3 )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d10 metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.

Evidence of 2D anti-ferromagnetic ordering in rare-earth Langmuir–Blodgett films

In recent years the ordering of spins in two-dimensions has received considerable attention due to both the fundamental physics interest and for the possible technological applications. Langmuir–Blodgett (LB) films with magnetic ions are ideal systems to study two-dimensional (2D) magnetic ordering as the distances of the magnetic-ions along the out-of-plane and in-plane directions differ by almost an order of magnitude and the effect of the substrate can be neglected. In particular, vortex formation in ferro and antiferro 2D magnetic structures are of current interest and LB films are ideal to study this evolving physics. We show here that 2D magnetic ordering along the in-plane direction of multilayered LB films changes from ferromagnetic to anti-ferromagnetic as the rare-earth magnetic ion is changed from Gadolinium (Gd) to Holmium (Ho). The in-plane magnetization results have shown that Gd based LB films exhibit a temperature dependent saturation moment due to the existence of a vortex structure. The results of the magnetization study presented here show that the Ho based LB films exhibit an in-plane anti-ferromagnetic ordering and the saturation moment is found to be almost independent of temperature indicating the absence of spin vortex structures. From a 1/χ − T plot the asymtotic Curie point θa and the Neel temperature θN of the Ho-St LB film were found to be 66 K and 42 K respectively.

Electrical properties of alternating acid and amino substituted calixarene Langmuir-Blodgett thin films

The Langmuir-Blodgett (LB) alternate layer fabrication technique provides one of the most effective methods to fabricate organic thin films in the nanoscale. The structure of these thin films could be controlled at the molecular scale by spreading a monolayer on an air-water interface followed by sequential transferring of this layer onto a selected solid substrate. These films can be utilized within optical, electrical and biological applications in many different fields. Within this paper, two calix[4]arenes containing either carboxylic acid or amino substituents were utilised to prepare multilayer LB films and to study the electrical characteristic of these films using I–V and C-f measurements. The resultant calix[4]acid/amine multilayers demonstrated a highly non-linear I–V behaviour which obeys a Schottky conduction mechanism.

Structural and optical properties of two-dimensional gadolinium stearate Langmuir monolayer

Langmuir-Blodgett (LB) films having large stack of amphiphilic-fatty-acids bearing rare-earth-ions are ideal two-dimensional magnetic systems to study spin-vortex ordering as the distances of the magnetic-ions along the out-of-plane and in-plane directions differ by an order of magnitude. Here we present results of in-situ X-ray scattering measurements on Langmuir monolayer of the amphiphilic stearic acid on the water surface containing Gadolinium ions to understand the formation process of monolayer and multilayer LB films on the substrates. Infrared spectroscopy and microscopy measurements were also carried out to understand the growth and transfer mechanism of the LB films.

Supramolecular Aggregates of Tetraphenylethene-Cored AIEgen toward Mechanoluminescent and Electroluminescent Devices.

Luminescent materials possessing both the mechanoluminescence (MCL) and electroluminescence (EL) properties are the quest for sensing and optoelectronic applications. We report on the synthesis of a new tailor-made luminogen, 1,2-bis(4-(1-([1,1'-biphenyl]-4-yl)-2,2-diphenylvinyl)phenyl)-1,2-diphenylethene (TPE 5), using Suzuki coupling reaction with high yield. An aggregation-induced emission (AIE) active complex TPE 5 forms supramolecular spherical aggregates at the air-water interface of a Langmuir trough. As a consequence, a large enhancement of luminescence is obtained from the mono- and multilayer Langmuir-Blodgett films of TPE 5 owing to the AIE effect. The luminogen TPE 5 exhibits a reversible MCL response, displaying photoluminescence switching due to change in the crystalline states under external stimuli. The unique feature of luminescence enhancement upon aggregate formation is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular aggregates as the active layer. This work demonstrates an efficient strategy for obtaining controlled supramolecular aggregates of AIEgen with a potential in the dual applications of MCL and EL.

Improvement of signal-to-noise ratio in oxygen sensitive emission from hybrid Langmuir–Blodgett films of amphiphilic iridium complexes with the exfoliated nanosheets using a metal layer

Cyclometalated Ir(III) complexes are attracting extensive attention due to their high emission properties in the visible region. Oxygen sensitive photoluminescence (PL) emissions from single- and multi-layered Ir(III) Langmuir–Blodgett (LB) films are measured. The single-layered LB film on a non-aluminum coated glass substrate shows oxygen sensitive PL emission but its intensity is very weak. In contrast, the multi-layered LB film shows higher intensity but their oxygen sensitivity is lower than that of the single-layered sample. To break the trade-off between intensity and sensitivity, PL characteristics from the LB film on an aluminum-coated glass substrate are investigated. The PL emission from the LB film on the metal layer show higher intensity and good oxygen sensitivity. The mechanism of the emission enhancement is also discussed in this paper.

Multilayer Langmuir-Blodgett films as diffractive external 3D photonic crystal in blue OLEDs.

Three-dimensional Langmuir-Blodgett films made of silica beads are theoretically and experimentally investigated in order to improve the relatively small efficiency of blue OLEDs. Using films made of 5 layers of beads, we fabricated OLEDs emitting at 476 nm, and measured a gain of around 40% on their external quantum efficiency. An optical model has been developed to accurately handle the fact that the organic emitting layer and the photonic extraction layer are separated by a distance greater than 1000 wavelength. The latter also permits to describe rapidly this three-dimensional optical OLED cavity, without redoing all the numerical simulations when the optical properties of the organic layers are changed (material index, thicknesses).

Factors affecting photocurrent generation performances of Langmuir–Blodgett films of tetraphenylporphyrin-bound acyl celluloses

Various Langmuir–Blodgett (LB) films of tetraphenylporphyrin (TPP)-bound acyl celluloses with different degrees of substitution of the TPP groups (DSTPP) and different acyl groups were prepared. TPP-bound acyl celluloses with DSTPP values less than 0.38 and myristoyl groups as the O-2 and O-3 substituents were suitable for obtaining LB mono-layer films with high quantum yields. The horizontal lifting method was better than the vertical dipping method for the deposition of LB films. The number of layers in LB multi-layer films of TPP-bound myristoyl cellulose with a DSTPP of 0.36 also influenced the quantum yield, and the quantum yield of the LB di-layer film was higher than those of the LB mono- and tri-layer films. This information will be useful in the improvement of the photocurrent generation performances of LB films of TPP-bound acyl celluloses.

Stability of J-aggregated species in an indocarbocyanine dye in Langmuir–Blodgett Films

Here, the stability behaviour of J-aggregate of an indocarbocyanine dye 1,1′-Dioctadecyl-3,3,3′,3′-Tetramethylindocarbocynine perchlorate (DiI) in fatty acid mixed (XDiI=0.4) Langmuir–Blodgett (LB) films under different condition was reported. Surface pressure–area per molecule (π–A) isotherm measurement suggest that the molecular interaction between the constituent molecules changes with subphase temperature. UV–vis absorption and fluorescence spectroscopy and Atomic Force Microscopy (AFM) were used to study the stability behaviour. It has been observed that prominent J-aggregate of DiI occurred in the mixed films at subphase temperature 15°C. With the passage of time as well as post heat treatment DiI J-aggregate decayed to excimer in both mono- and multilayer LB films. Total transition from J-aggregate to excimer occurred in monolayer films, whereas, the transition was partial in multilayer films. The stability of DiI J-aggregate in monolayer films was increased by two ways – (i) depositing the DiI-SA mixed LB films at higher surface pressure, (ii) exposing the films at 50°C for 5min. It has been observed that after heat treatment the DiI J-aggregate remained almost stable even after 200 days. AFM investigations gave the compelling visual evidences of the same.

Nanostructured LB films developed from poly(p-acryloylaminophenylmethylphosphonic) acid

ABSTRACTIn this paper, the formation of Langmuir-Blodgett films of poly(p-acryloylaminophenylmethylphosphonic) acid polymers, with general formula (C10H12NPO4)n are reported. The Langmuir-Blodgett (LB) technique was used for building ordered nanostructures in molecular assemblies of these polymers, which were able to form stable films. At the air-water interface, these polymers (with low and high molecular weight) formed Langmuir (L) monolayers, which were characterized by surface pressure versus molecular area (π-A) isotherms and Brewster´s Angle Microscopy (BAM). Using the LB method, molecular mono and multilayer films of these polymers were prepared and transferred onto glass substrates forming Z-type multilayers, with a transfer ratio close to unity. These LB films were characterized by Atomic Force Microscopy (AFM).

Dye distance mapping using waveguide evanescent field fluorescence microscopy and its application to cell biology.

Previous studies have measured the distance between cells and the substratum at sites of adhesion via the emission of a fluorescent dye and waveguide methods. Here, we demonstrate a novel approach to measure the position of fluorescent dyes above a waveguide surface in the 10-200 nm distance range throughout an entire area, yielding a 2D dye distance map or a 3D contour plot. The dye is located in a multilayered Langmuir Blodgett (LB) film or in the plasma membrane of a cell. Waveguide evanescent field fluorescence (WEFF) images obtained using two different waveguide modes are employed allowing, with a simple mathematical approach, the calculation of dye distance maps. Ultra-thin steps made using LB technology, adhesion distances and the bending of the plasma membrane between focal adhesions of osteoblastic cells are shown as examples. The errors are discussed. False color representation of a dye distance map with four osteoblasts. The inset represents an overexposed WEFF image of the same field of view.

Synthesis, electrochemical and spectroelectrochemical properties of novel phthalocyanine complexes of manganese, titanium and indium

The new tetra peripheral 3,5-bis(trifluoromethyl)phenylethynyl substituted metallophthalocyanines (MPc) have been synthesized and their aggregative properties were investigated in different concentrations. Voltammetric and in situ spectroelectrochemical characterization of MPcs bearing metal centers with higher oxidation states InIII, MnIII, and TiIV were performed in solution. While InIIIClPc gave only Pc ring based reduction process, MnIIIClPc and TiIVOPc showed metal based reduction reactions in addition to Pc-based redox processes. The presence of redox active metal centers like MnIIICl and TiIVO in the core of Pc ring increases the electrochemical activity of the complexes. The redox responses of the complexes confirmed the submitted structure of the complexes. During the electrochemical measurements, it was noticed that the presence of molecular oxygen in the electrolyte system considerably influenced the redox responses of the complexes due to the interaction of MPcs with O2, which indicated the electrocatalytic and/or electrochemical sensing activities of the complexes for O2 sensing. Electrocatalytic oxygen reduction and oxygen sensing measurements were performed in solution and in solid states as Langmuir-Blodgett multilayer thin films. While InIIIClPc did not give any voltammetric signal for the interaction with molecular oxygen, square wave voltammetric (SWV) responses of MnIIIClPc and TiIVOPc show electrocatalytic activities of the complexes for oxygen reduction reactions (ORR). Moreover, interaction of O2 with these complexes gave extraordinary anodic SWV signals in both of aprotic and protic solvents, which indicate possible usage of the complexes as molecular oxygen sensor.

Langmuir-Blodgett films of self-assembled (alkylether-derivatized Zn phthalocyanine)-(C₆₀ imidazole adduct) dyad with controlled intermolecular distance for photoelectrochemical studies.

A multilayer Langmuir-Blodgett (LB) film of the self-assembled electron donor-acceptor dyad of Zn phthalocyanine, appended with four long-chain aliphatic ether peripheral substituents, and an imidazole adduct of C60 was prepared and applied as a photoactive material in a photoelectrochemical cell. Changes in the simultaneously recorded surface pressure and surface potential vs area per molecule compression isotherms for Langmuir films of the dyad and, separately, of its components helped to identify phase transitions and mutual interactions of molecules in films. The Brewster angle microscopy (BAM) imaging of the Langmuir films showed circular condensed phase domains of the dyad molecules. The determined area per molecule was lower than that estimated for the dyad and its components, separately. The multilayer LB films of the dyad were transferred onto hydrophobized fluorine-doped tin oxide-coated (FTO) glass slides under different conditions. The presence of both components in the dyad LB films was confirmed with the UV-vis spectroscopy measurements. For the LB films transferred at different surface pressures, the PM-IRRAS measurements revealed that the phthalocyanine macrocycle planes and ether moieties in films were tilted with respect to the FTO surface. The AFM imaging of the LB films indicated formation of relatively uniform dyad LB films. Then, the femtosecond transient absorption spectral studies evidenced photoinduced electron transfer in the LB film. The obtained transient signals corresponding to both Zn(TPPE)(•+) and C60im(•-) confirmed the occurrence of intramolecular electron transfer. The determined rate constants of charge separation, kcs = 2.6 × 10(11) s(-1), and charge recombination, kcr = 9.7 × 10(9) s(-1), indicated quite efficient electron transfer within the film. In the photoelectrochemical studies, either photoanodic or photocathodic current was generated depending on the applied bias potential when the dyad LB film-coated FTO was used as the working electrode and ascorbic acid or methylviologen, respectively, as the charge mediator in an aqueous solution.

Adsorption and enzyme activity of sucrose phosphorylase on lipid Langmuir and Langmuir–Blodgett films

The production of bioelectronic devices, including biosensors, can be conducted using enzymes immobilized in ultrathin solid films, for which preserving the enzymatic catalytic activity is crucial for optimal performance. In this sense, nanostructured films that allow for control over molecular architectures are of interest. In this paper, we investigate the adsorption of sucrose phosphorylase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid, which caused the surface pressure isotherms to expand. With polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), the amide bands from the enzyme could be identified, with the C–N and C=O dipole moments lying parallel to the air–water interface. Structuring of the enzyme into an α-helix was noted, and this structure was preserved when the mixed enzyme-phospholipid monolayer was transferred in the form of a Langmuir–Blodgett (LB) film. The latter was demonstrated with measurements of the catalytic activity of sucrose phosphorylase, which presented the highest enzyme activity for multilayer LB film. The approach presented in this study not only allows for optimized catalytic activity toward sucrose but also permits to explain why certain film architectures exhibit superior performance.

Nanoscale Growth of CdS and PbS Semiconductor within Calix[4]Arene Langmuir-Blodgett LB Film for Ion Sensing Application

The characteristics of cadmium sulphide (CdS) and lead sulphide (PbS) nanoparticles, grown inside Langmuir-Blodgett (LB) multilayer films of 5,11,17,23-tetra-tert-butyl-25,27-dicarboxymethoxy-26,28-dihydroxycalix [arene (I), have been studied using ellipsometry, UV-visible spectroscopy, and transmission electron microscopy (TEM). Multilayer films were formed by transferring a floating Langmuir monolayer of I onto substrates using LB deposition and water subphase containing Pb2+or Cd2+ions. The nanoparticles were fabricated by exposing cadmium-or lead-containing multilayer films of I (20-80 monolayers thick) to hydrogen sulphide (H2S) gas for 12 hours. By Gaussian fitting of the absorbance - energy spectra, the size of the clusters and their dispersion were found to be 1.43±0.18 nm and 1.21±0.05 nm for CdS and PbS respectively. This is the first time that such thick LB films of an amphiphilic compound possessing such high thermal stability (m.pt. ~270°C) have been used as the vehicle for the formation of CdS and PbS semiconductor particles.

Thermal stability of organic layered systems based on lead stearate

The structural variation in multilayer Langmuir-Blodgett films of lead stearate caused by heat treatment under different conditions in the temperature range 20–100°C is investigated by X-ray reflectometry and high-resolution electron diffraction. Successive annealing of the samples is shown to not alter the initial layered structure at temperatures of 60, 80, and 100°C; partial disturbance of the layered structure occurs upon successive annealing at 80°C and 100°C. Significant disturbance of the structure is observed when the films are heated immediately to 100°C. In all these cases, the orthorhombic (pseudomonoclinic) lattice, with the lattice constants: a = 0.496, b = 0.738, c = 9.60 nm, α = β = γ = 90°, space group P2/1b, formed by transferring monolayers onto the substrate is retained in the crystalline domains of the film.

A heterostructured SnO2–TiO2 thin film prepared by Langmuir–Blodgett technique

SnO2–TiO2 heterostructure films were prepared through Langmuir–Blodgett (LB) route. LB films of octadecyl amine (ODA)–titanyl oxalate multilayer deposited on Si (100) and decomposed at 600 °C showed rutile and anatase phases of ultrathin TiO2 film. Subsequently, multilayer LB film of ODA–stannate deposited on the pre deposited TiO2 film after decomposition at 600 °C resulted in thin SnO2 films on the TiO2 thin film. The phase analysis of the SnO2–TiO2 film showed cassiterite phase of SnO2 as well as the rutile/anatase mixture of TiO2 indicating a SnO2–TiO2 heterostructured film. Surface morphology of the pure TiO2 film and SnO2–TiO2 film were analyzed by using AFM. Electrical characterization by AC impedance analysis suggested SnO2–TiO2 heterostructure formation. DC current voltage measurement showed increase in photocurrent indicating visible light absorption and efficient charge separation under the sunlight type radiation.