Blodgett Technique Research Articles

PH effect in Langmuir–Blodgett self-assembly of MoS2 and WS2 thin films

We reported Langmuir–Blodgett films of molybdenum disulphide and tungsten disulfide and studied the formation of MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} and WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} layers. The effect of the subphase pH is investigated. Also, the influence of the subphase conditions on the number of layers was reported. By varying the pH of the buffer solution subphase, the solvent-to-nanoparticle interaction is changed and the compression of the layer during deposition is influenced. The stacking of the MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} and WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} crystalline structure under the influence of subphase pH and the material concentration were investigated. Langmuir layers assembly is a useful method to manipulate the distribution of WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} and MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document}. Successful deposition of dichalcogenides at the air–water interface on silicon substrate was performed using Balance Langmuir–Blodgett technique. The characterization of WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} and films MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} with X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy was carried out.

The effect of nanobubbles on Langmuir-Blodgett films

Nanobubbles (NBs) are classified in two distinct categories: surface and bulk. Surface NBs are readily observed using atomic force microscopy (AFM), while the existence of bulk NBs has been a subject of debate, conflicting with the diffusion theory's predictions. Current methodologies for identifying bulk NBs yield inconclusive results. In this study, Langmuir Blodgett (LB) technique and AFM, are utilized to visualize NB imprints on anionic, cationic and zwitterionic lipid films deposited on glass-slide substrates. Our analysis of Langmuir monolayers compression isotherms reveals the impact of bulk NBs on lipid monolayer development. AFM scans of the deposited lipid films consistently show NB imprints. Notably, cationic and zwitterionic film depositions exhibit NB formations from the 1st layer, whereas in anionic films, these formations are observed only after the 3rd layer. These results suggest that the origin of these imprinted formations may be attributed to bulk NBs.

Controllable-assembled functional monolayers by the Langmuir–Blodgett technique for optoelectronic applications

Systematic review of the application of controllable assembled LB films in combination with optoelectronic applications.

Biofuels and hydrogen production: back to the Langmuir–Blodgett approach for large-scale structuration of Bi-based photoelectrodes

This perspective article highlights the good potentiality for the Langmuir Blodgett technique to produce massively BiVO4 based photoelectrodes for biomass valorization and hydrogen production in the context of Brazil's decarbonation.

Ruthenium complex based nanocomposite film with enhanced and selective electrochemical sensing of bifenthrin pesticide.

Bifenthrin (BF), a widely used pyrethroid pesticide in farming, lacks highly sensitive and selective sensors despite its extensive application. Ruthenium complexes are very effective for selective sensing applications but suffer from structural instability at elevated conditions, electrochemical activity, and the use of costly electrolytes. This work improves their electrochemical activity and mechanical strength by incorporating silver nanowires and replacing the costly electrolyte with abundant KCl + PBS, resulting in enhanced signal performance. Herein, a ruthenium complex containing composite film was immobilized on a platinum (Pt) electrode using Langmuir Blodgett technique. The fabricated sensor has been characterized by differential pulse voltammetry (DPV) based electrochemical technique. The BF pesticide sensing parameters, including the limit of detection (LOD), linear range (LR), and sensitivity, were evaluated using SWV, DPV, and CV techniques. Among these, the DPV technique demonstrated the best performance, achieving a sensitivity of 0.648 μA cm-2 μM-1, a LR of 1-10 μM, and a LOD of 1 μM. The relative standard deviation (RSD) values using DPV are found to be 6.3% (repeatability study), 3% (reproducibility study), 8% (metal ion interference), 5% (organic species interference), and 2% (real sample study), which are much lesser than the World Health Organization (WHO) recommendation of RSD value on the pesticide (i.e. 20%). The BF sensor demonstrated a selectivity of 2× difference of peak height response compared to similar pesticides. The reported pesticide sensor will open new options for sensor research using metal complex-based LB film nanocomposite.

Real-time topography inspection of DPPC monolayers using a surface-plasmon resonance sensor

This paper presents an alternative optical characterization of biosensors based on supported lipid monolayers (SLMs). Developing these biosensors requires precise thickness characterization of the films to understand their structure and dynamics. This paper proposes an optical technique to measure the thickness, optical properties, and location of a dipalmitoyl-phosphatidylcholine (DPPC) SLM on top of a metallic thin film. DPPC SLMs are of interest for biosensing applications, such as detecting pulmonary-related infections like SARS-CoV-2, Avian Influenza, and the H1N1 influenza virus. The monolayer was fabricated using the Langmuir–Blodgett technique, and the experimental characterization consisted of measuring the surface-plasmon resonance angle in the Kretschmann configuration. This technique provides an alternative option for real-time visual inspection and determination of the location and shape of DPPC monolayers in large areas. Therefore, it offers a useful tool for further developing SLM-based biosensors.

Enhanced luminescence and electrical conductivity of polymer ultrathin films doped with TiO2 nanoparticles

The chemical polymerization method was used to prepare nanocomposite materials of polyaniline (PANi) and Titanium dioxide (TiO2) nanoparticles. Ultrathin films were deposited by using the Langmuir Blodgett (LB) Technique. Surface Pressure vs mean molecular area isotherms of nanocomposite materials showed an increase in maximum attained surface pressure with variation in nanoparticle doping concentration. Photoluminescence (PL) spectra were taken for LB multilayers deposited on a quartz substrate, an increase in the intensity of PL peaks with increasing doping concentration of TiO2 nanoparticles. The topography of LB monolayer film under atomic force microscopy (AFM) revealed that films were uniformly and densely deposited on the substrate. Phase imaging ensured the presence of nanoparticles in the polymer matrix. Conductive atomic force microscopy (C-AFM) was used to investigate the local electrical properties of nanocomposite LB films. Current-voltage characteristics showed variation in current with changing doping concentrations of TiO2 nanocomposite in PANi matrix. The work presents new insights in analyzing uniformly deposited ultrathin films of the composites which can be probed by C-AFM to reveal local electric properties by understanding topography-current correlation at the nanoscale. The conductive data analysis could be useful for understanding the current flow through the nanostructure surface.

Construction of Amphiphilic Indocyanine–Green–Based Langmuir Film and Drop–Casting Film with Photoelectric Conversion Properties

Molecular self–assembly is the automatic formation of functional assemblies of different structural components through weak, reversible, non–covalent interactions on the basis of molecular recognition. Amphiphilic molecules have a natural advantage in self–assembly at the gas/liquid interface. In this work, two amphiphilic molecules with a special molecular structure, indocyanine green (ICG) and a derivative of indocyanine green (CCS), were combined with two dye molecules (tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) and nickel (II) phthalocyanine–tetrasulfonic acid tetrasodium salt (TsNiPc) for self–assembly through the Langmuir–Blodgett (LB) technique. The nanostructure and assembly behavior in ordered self–assembled films are effectively regulated by inducing dye molecules to form different types of aggregates (H– and J–aggregates). In addition, we prepared composite films containing the same functional components using the conventional drop–casting technique and performed a series of comparative experiments with LB films. The degree of hydrophilicity was found to be related to roughness, with LB composite films being flatter and denser, with the lowest roughness and the best hydrophobicity compared to drop–casting films. Notably, the LB films showed better optoelectronic properties under the same conditions, providing new clues for the application of optoelectronic functional ultrathin film devices.

Langmuir–Blodgett films of magnetic nanowires

One-dimensional magnetic nanomaterials are scientifically interesting and of great importance due to their morphology-dependent properties. As a consequence of magnetic interactions between magnetic nanowires (MNWs) their bottom-up assembly remains a tough challenge. For the first time, using the Langmuir–Blodgett (LB) technique, we prepared two-dimensional (2D) large scale LB films of MNWs, which were synthesized by template directed electrodeposition method, on glass substrates. Using a plastic pipette, MNWs dispersed in chloroform were spread on the surface of the pure water subphase in a Teflon trough. After the stabilization of the monolayer, the Langmuir film was compressed and the surface pressure-area isotherm was recorded. By pulling up the substrate through the Langmuir film, mono- and bilayers of MNWs were deposited on the substrates at the target surface pressures of 10 mN/m and 15 mN/m. The surface pressure isotherm and field emission scanning electron microscope (FE-SEM) images showed that MNWs were successfully transformed onto the substrates. FESEM micrographs showed that the assembly of MNWs was different from that of metallic nanowires. Furthermore, the results showed that rotating the substrate by 90 degrees, after the deposition of the first layer, and then depositing the second layer on it does not lead to the creation of a hierarchical structure. These results open up new opportunities for the applications of magnetic nanomaterials in physical and chemical sensors, data-storage media and magnetic switching devices. Besides, this study affords fundamental insights into the formation of magnetic monolayers and multilayers.

Insights on the Molecular Orientation of Oligo(p-phenylene vinylene) Derivatives with Alkyl Chains in Langmuir Films

One of the oligo(p-phenylene vinylene) derivatives having alkyl chains, OPV-1, is known to form characteristic rod-shaped nanoaggregates on the water surface, and thin films with aligned nanoaggregates can be obtained by the Langmuir–Blodgett (LB) technique. Although the molecular aggregation and orientation of the “conjugated rings part” in the LB films have already been investigated, analysis of the detailed molecular structure involving the “alkyl chains” is left behind. In the present study, to reveal the role of the alkyl chains in the molecular aggregation in Langmuir films prior to the LB transfer, infrared (IR) external reflection spectroscopic measurements on the water surface are carried out. It has been revealed that not only the conjugated rings of OPV-1 but also the alkyl chains with an ordered conformation are lying on the water surface. The characteristic orientation is found to be kept on a solid substrate even after the LB transfer by IR p-polarized multiple-angle incidence resolution spectrometry (pMAIRS). In addition, pMAIRS was first employed for analyses of the biaxial orientation in the LB films, and the molecular orientations for the conjugated rings and the alkyl chains were quantitatively evaluated from both in-plane and out-of-plane perspectives.

Portable and Room Temperature Operating H2S Gas Detection and Alert System Using Nanocrystalline SnO2 Thin Films

Portable, compact, wireless and hand held electronic alarm which can detect Hydrogen Sulphide (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S) gas at room temperature from 1 ppm to 40 ppm is fabricated using nanostructured Tin oxide (SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) thin film deposited on quartz using Langmuir Blodgett (LB) technique. It was demonstrated that SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film with gold contacts works as a chemiresistive, selective and sensitive sensor for H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas at room temperature. Few SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films were studied for extracting the sensitivity and accuracy parameters of the sensor. Using the optimized parameters, an electronic alarm with less than 5 V input power requirement was fabricated to make it inherently safe for explosive environments. Specificity, reliability and stability studies of the sensors showed satisfactory performance for using these sensors for monitoring H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S leak. Along with 3D printed light weight gas sensor housing, it makes a hazard free, compact, reliable and versatile sensing device.

Mechanistic insights into the deformation and degradation of a 2D metal organic framework

2D metal-organic frameworks (2D-MOFs) materials can be subjected to various modes of mechanical stresses and strains in a wide range of applications, for which their mechanical properties are critical to reach practical implementations. Despite the rapid developments focused on the preparation of ultrathin 2D-MOF materials, very little is known about their mechanical and degradation behavior. Here, we use the established 2D-MOF PdTCPP-Cu (NAFS-13) as model system, to introduce the Langmuir–Blodgett (LB) technique, combined with interfacial rheology, as a novel in situ method for direct determination of the in-plane Young’s modulus by simultaneously measuring the 2D shear and compression moduli of a 2D-MOF formed at the air-water interface. Furthermore, it can be used to evaluate mechanistic models describing the degradation kinetics of 2D MOFs. To provide a deeper understanding of the factors that determine the Young’s modulus observed in such a set up, we carried out nanoindentation measurements and molecular dynamics (MD) simulations based on classical force fields. This protocol allows us to gain mechanistic insights into the impact of structural defects, temperature, tensile and compression stress on the Young’s modulus of 2D MOFs.

Mengkaji Kesan Kekonduksian Pengenapan Politiofena / Polipirol /Polianilina (PT /PPY /PANI) di Atas Kaca Indium Timah Oksida (ITO)

The conducting polymer family is widely used in the field of polymer-based sensors. Among the polymers that are often used are polyaniline (PANI), polypyrrole (PPY) and polythiophene (PT). Sensors operate based on the production of signals by analyte molecules which then produce measurements either qualitatively or quantitatively. In addition, the use of conducting polymers in the field of biosensing has highlighted its importance, especially in the fields of biomedicine, environment, food quality control and more. Even so, there are issues that often arise such as controlling and producing signals of the materials used. Appropriate materials and methods also need to be studied. Therefore, this study was conducted to examine the conductivity effect of the deposition of Polythiophene / Polypyrrole / Polyaniline (PPY/ PT/PANI) on Indium Tin Oxide (ITO) Glass. Polyaniline monolayer (PANI) was deposited on the surface of indium tin oxide (ITO) glass using the Langmuir Blodgett (LB) technique. The monolayer surface of PANI particles has been coated with a layer of polypyrrole (PPY) and polythiophene (PT). PPY and PT were dissolved in methanol and then added with p-toluene sulfonic acid (PTSA) to give the same effect as PANI, especially on their back chain structure. The UV-Vis and FTIR spectra prove the existence of peaks resulting from the solubility and doping process against PPY and PT. It was found that the uneven size of the polymer molecules results from the PPY / PANI image because there is a probability that the existing PPY clumps with each other. When PT was applied to the PPY / PANI layer, a combination of the three polymers formed a cavity on the surface of the PT / PPY / PANI layer. It was explained by the analysis of FTIR PT / PPY / PANI which exhibits the existence of bonds between the combined polymers. The material resistance decreases when the three polymers were combined which explains the higher conductivity value obtained.

Preparation and Surface Characterization of Chitosan-Based Coatings for PET Materials.

Poly(ethylene terephthalate)-PET-is one of the most frequently used polymers in biomedical applications. Due to chemical inertness, PET surface modification is necessary to gain specific properties, making the polymer biocompatible. The aim of this paper is to characterize the multi-component films containing chitosan (Ch), phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), immunosuppressant cyclosporine A (CsA) and/or antioxidant lauryl gallate (LG) which can be utilized as a very attractive material for developing the PET coatings. Chitosan was employed owing to its antibacterial activity and also its ability to promote cell adhesion and proliferation favorable for tissue engineering and regeneration purposes. Moreover, the Ch film can be additionally modified with other substances of biological importance (DOPC, CsA and LG). The layers of varying compositions were prepared using the Langmuir-Blodgett (LB) technique on the air plasma-activated PET support. Then their nanostructure, molecular distribution, surface chemistry and wettability were determined by atomic force microscopy (AFM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), contact angle (CA) measurements and the surface free energy and its components' determination, respectively. The obtained results show clearly the dependence of the surface properties of the films on the molar ratio of components and allow for a better understanding of the coating organization and mechanisms of interactions at the molecular level both inside the films and between the films and the polar/apolar liquids imitating the environment of different properties. The organized layers of this type can be helpful in gaining control over the surface properties of the biomaterial, thus getting rid of the limitations in favor of increased biocompatibility. This is a good basis for further investigations on the correlation of the immune system response to the presence of biomaterial and its physicochemical properties.

Langmuir and Langmuir-Blodgett Films of Gold and Silver Nanoparticles.

Recently the focus of the Langmuir-Blodgett technique as a method of choice to transfer monolayers from the air/water interface onto solid substrates in a controllable fashion has been shifting toward purely hydrophobic gold and silver nanoparticles. The fundamental interactions between particles that become relevant in the absence of polar groups range from dispersive attractions from the metal cores and repulsions between ligand shells to weaker entropic factors. The layer evolution is explored, starting with interfacial self-assembly upon solution spreading and domain and circular island formation, which subsequently merge into a complete monolayer and finally form multilayers or macroscopic wrinkles. Moreover, structural properties such as the core:ligand size ratio are investigated in the context of dispersive forces, whereby the nanoparticles with small cores and long ligands tend not to aggregate sufficiently to produce continuous films, those with large cores and short ligands were found to aggregate irreversibly, and those in between the two extremes were concluded to be able to form highly organized crystalline films. Similarly, the characteristics of the spreading solution such as the concentration and the solvent type crucially influence the film crystallinity, with the deciding factor being the degree of affinity between the capping ligand and the solvent used for spreading. Finally, the most common strategies employed to enhance the mechanical stability of the metal nanoparticle films along with the recent attempts to functionalize the particles in attempts to improve their applicability in the industry are summarized and evaluated in relation to their future prospects. One of the objectives of this feature article is to elucidate the differences between hydrophobic metal nanoparticles and typical amphiphilic molecules that the majority of the literature in the field describes and to familiarize the reader with the knowledge required to design Langmuir-Blodgett nanoparticle systems as well as the strategies to improve existing ones.

Surface-Enhanced Raman Spectroscopy (SERS) Chemical Enhancement in the Vibronically Coupled Langmuir Layer of Mixed Dichalcogenide 1T-MoSSe with Adsorbed R6G

Transition-metal dichalcogenides based on different chalcogen atoms give origins to many new phenomena due to symmetry breaking and exhibit better physicochemical characteristics than pristine dichalcogenides. In this work, the formation of a perfectly tiled uniform monolayer of MoSSe using the Langmuir–Blodgett (LB) technique under ambient conditions is demonstrated. The aligned monolayer of the 1T phase depicts a film thickness of 1.2–2.4 nm corresponding to a single to a bilayer of MoSSe. The LB-prepared substrates are subsequently used for Raman sensing of R6G. The presence of MoSSe quenches the fluorescence of the R6G. Regarding surface-enhanced Raman spectroscopy sensitivity, 1T MoSSe could sense R6G up to picomolar concentrations with an enhancement factor of ∼6 × 106. This is 3 to 4 orders higher than the corresponding sulfide or the selenide analogues (1T MoS2 and 1T MoSe2). This increased sensitivity of 1T MoSSe is attributed to a large number of active sites with intrinsic dipole moment and high electronic conductivity, which leads to strong substrate-analyte vibronic coupling. Absorption and Raman spectroscopy confirms the static coupling between the substrates and R6G molecules. First principle density functional theory calculations reveal high density of states near the Fermi level in the case of distorted 1T MoSSe as compared to the pristine sulfide or selenide with less energy difference between the highest occupied molecular orbital of R6G and the Fermi level of 1T MoSSe. This might result in a facile charge transfer during the photoinduced charge transfer-driven chemical mechanism leading to a strong coupling of the metal–analyte complex, thus resulting in significant Raman enhancement.

Nanostructured CeO2 ultrathin film deposited by the Langmuir Blodgett technique for highly sensitive and specific detection of sub ppm level NO2 gas at room temperature

Room temperature NO2 sensor based on ultrathin CeO2 deposited by LB technique was fabricated. High sensing and selectivity to ppb level NO2 gas was observed due to large number of surface adsorbed oxygen species on nanostructure CeO2 surface.

Surface Properties of the Polyethylene Terephthalate (PET) Substrate Modified with the Phospholipid-Polypeptide-Antioxidant Films: Design of Functional Biocoatings.

Surface properties of polyethylene terephthalate (PET) coated with the ternary monolayers of the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the immunosuppressant cyclosporine A (CsA), and the antioxidant lauryl gallate (LG) were examined. The films were deposited, by means of the Langmuir-Blodgett (LB) technique, on activated by air low temperature plasma PET plates (PETair). Their topography and surface chemistry were determined with the help of atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), respectively, while wettability was evaluated by the contact angle measurements. Then, the surface free energy and its components were calculated from the Lifshitz-van der Waals/Acid-Base (LWAB) approach. The AFM imaging showed that the Langmuir monolayers were transferred effectively and yielded smoothing of the PETair surface. Mass spectrometry confirmed compatibility of the quantitative and qualitative compositions of the monolayers before and after the transfer onto the substrate. Moreover, the molecular arrangement in the LB films and possible mechanisms of DOPC-CsA-LG interactions were determined. The wettability studies provided information on the type and magnitude of the interactions that can occur between the biocoatings and the liquids imitating different environments. It was found that the changes from open to closed conformation of CsA molecules are driven by the hydrophobic environment ensured by the surrounding DOPC and LG molecules. This process is of significance to drug delivery where the CsA molecules can be released directly from the biomaterial surface by passive diffusion. The obtained results showed that the chosen techniques are complementary for the characterization of the molecular organization of multicomponent LB films at the polymer substrate as well as for designing biocompatible coatings with precisely defined wettability.

Two-Dimensional Layered Organic-Inorganic Hybrid Perovskite Thin-Film Fabrication by Langmuir-Blodgett and Intercalation Techniques.

We demonstrate the formation of a well-organized thin film of two-dimensional (2D) layered (C18H37NH3)2PbI4 hybrid perovskite by immersing octadecyl amine (ODA) Langmuir-Blodgett (LB) films in an aqueous solution of PbI2/HI. The immersed films exhibit a sharp absorption band at 486 nm (2.55 eV), which is assigned to the excitonic absorption. The film exhibits a bright green emission under ultraviolet light at room temperature. The photoluminescence spectrum has a distinct peak at 497 nm (2.49 eV) and is a mirror image of the absorption spectrum. X-ray diffraction (XRD) analyses reveal that the film has a bilayer-like structure with a d-spacing of 6.4 nm, which is equal to that of a (C18H37NH3)2PbI4 perovskite single crystal with a quantum well (QW) structure. Only intense peaks of the (0 0 l) (l = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24) reflections are observed in the out-of-plane XRD pattern, indicating that the c axis is vertically oriented with respect to the substrate surface, and the orientational order is remarkably high. Fourier transform infrared spectroscopy reveals that the ODA molecules are protonated in the PbI2/HI solution. These results suggest that the nitrogen atoms of the ODA molecules in the film are protonated in the PbI2/HI solution, and then, inorganic layers of the PbI6 octahedra are intercalated in the alkyl ammonium film to neutralize the positive charge and form a QW structure. Fluorescence microscopy observation reveals that the 2D layered (C18H37NH3)2PbI4 film has a relatively uniform surface, reflecting the well-organized layered structure of the base material (ODA LB film). Because the intercalation process can be applied to various metal cations and halogen anions, we believe that the proposed technique will aid in the development of highly efficient 2D layered organic-inorganic hybrid perovskite materials.

Interaction of Lipophilic Cytarabine Derivatives with Biomembrane Model at the Air/Water Interface.

Cell membrane models are useful for obtaining molecular-level information on the interaction of biologically active molecules whose activity is believed to depend also on their effects on the membrane. Cytarabine was conjugated with fatty acids to improve the drug lipophilicity and the interaction with the biomembrane model. Cytarabine was conjugated with fatty acids of different lengths to form the trimyristoyl cytarabine and the tristearoyl cytarabine derivatives. Their interaction with biomembrane models constituted by dimyristoylphosphatidylcholine (DMPC) monolayers was studied by employing the Langmuir–Blodgett technique. DMPC/cytarabine, DMPC/trimyristoyl cytarabine and DMPC/tristearoyl cytarabine mixed monolayers at increasing molar fractions of the compound were prepared and placed on the subphase. The mean molecular area/surface pressure isotherms were recorded at 37 °C. Between the molecules of DMPC and those of cytarabine or prodrugs, repulsive forces act. However, these forces are very weak between DMPC and cytarabine and stronger between DMPC and the cytarabine derivatives, thus avoiding the expulsion of the compounds at higher surface pressure and modifying the stability of the mixed monolayer. The fatty acid moieties could then modulate the affinity of cytarabine for biomembranes.