Modified Langmuir-Blodgett Technique Research Articles

Lead halide perovskite nanowires stabilized by block copolymers for Langmuir-Blodgett assembly

The rapid development of solar cells based on lead halide perovskites (LHPs) has prompted very active research activities in other closely-related fields. Colloidal nanostructures of such materials display superior optoelectronic properties. Especially, one-dimensional (1D) LHPs nanowires show anisotropic optical properties when they are highly oriented. However, the ionic nature makes them very sensitive to external environment, limiting their large scale practical applications. Here, we introduce an amphiphilic block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-P4VP), to chemically modify the surface of colloidal CsPbBr3 nanowires. The resulting core-shell nanowires show enhanced photoluminescent emission and good colloidal stability against water. Taking advantage of the stability enhancement, we further applied a modified Langmuir-Blodgett technique to assemble monolayers of highly aligned nanowires, and studied their anisotropic optical properties.

Photocatalytic Properties of Thermally Annealed Films of Titanium Butoxide-=SUP=-*-=/SUP=-

We show that titanium dioxide particles capable of Reactive oxygen species generation can be produced in titanium butoxide films by annealing them at 500oC. Optimal conditions for the films deposition by a modified Langmuir-Blodgett technique were selected basing on the film uniformity examined by optical and electron microscopy. The photocatalytic activity of the annealed film was tested using RNO sensor bleaching.

Application of electrospray spreading to a modified Langmuir–Blodgett technique for organo-clay hybrid film preparation

A clay mineral, montmorillonite, is exfoliated into discrete clay nanosheets bearing negative charges in aqueous dispersions. When amphiphilic cations are spread on a surface of a clay mineral dispersion, clay nanosheets adsorb onto a floating film of the amphiphilic cations, forming a hybrid film. In conventional procedures, a solution of an amphiphilic cation is spread on a dispersion by manual operation. In this work, we instead applied an electrospray (ES) spreading method. A chloroform solution of octadecylammonium chloride (ODAH+Cl−) was spread on clay mineral dispersions by ES method at different infusion rates. The surface pressure-molecular area isotherm curves of the films exhibited the unusual dependence on the infusion rates; the curves shifted to a larger molecular area with the increase of infusion rate, while they shifted back to a smaller area with the further increase of infusion rate. The following formation mechanism was proposed. In case of the low infusion rate, the solution drops were so fine that some evaporated before they arrived at the interface. Under these conditions, the hybrid film contained ODAH+Cl− salt particles. In case of the high infusion rate, the large solution drops hit violently the dispersion surface, affording a hybrid film with multi-layered domains.

Probing Electrochemical Structure-Property Relationships at Non-Porous Monolayer Electrodes of Exfoliated Graphene and MoS2 Single Layers

The electrochemically available surface area and porosity of 2D materials is difficult to control due to the strong aggregation and restacking phenomena that occur when single layers are processed into thin or thick film electrodes. Furthermore, the distributed resistance, the potential for pore-size related effects and the uncertainty in relating estimated surface area and porosity data to the actual electrochemically accessible surface area make measurements of the intrinsic electrochemical performance of these materials difficult to assess. Ideally, electrochemical measurements are carried out on flat, polished or atomically flat electrode surfaces for the evaluation of intrinsic double-layer capacitance and electrochemical rate constants. In this talk, we will discuss our efforts to create large-area monolayers of solution exfoliated 2D materials for electrochemical evaluation in aqueous and non-aqueous electrolytes. Using a modified Langmuir-Blodgett technique, we demonstrate the ability to create uniform and large area monolayers of graphene oxide, thermally reduced graphene oxide as well as 1T and 2H molybdenum disulfide which can be transferred to atomically flat electrode substrates such as highly oriented pyrolytic graphite. These films are found to be stable during electrochemical cycling in various electrolytes and allow us to probe electrochemical properties as a function of 2D material structure without porosity-related artifacts. This model system has been used to probe the changes in double-layer capacitance in both aqueous and non-aqueous electrolytes for graphene-based materials as a function of defect density. It has allowed us to estimate the theoretical limits of graphene-based supercapacitors as a function of graphene “type”. More recently, this analysis has been extended to probe the intrinsic capacitance of the metallic 1T and semiconducting 2H polymorphs of MoS2 as a function of layer number to probe the charging mechanisms at play. The system also offers the ability to probe the capacitance of graphene/MoS2 heterostructures. These and future studies are expected to provide valuable insight into how we might build more energy dense supercapacitors from the optimal combination of 2D materials.

A wearable, highly stable, strain and bending sensor based on high aspect ratio graphite nanobelts

A simple and scalable method was developed for the fabrication of wearable strain and bending sensors, based on high aspect ratio (length/thickness ∼103) graphite nanobelt thin films deposited by a modified Langmuir–Blodgett technique onto flexible polymer substrates. The sensing mechanism is based on the changes in contact resistance between individual nanobelts upon substrate deformation. Very high sensor response stability for more than 5000 strain–release cycles and a device power consumption as low as 1 nW were achieved. The device maximum stretchability is limited by the metal electrodes and the polymer substrate; the maximum strain that could be applied to the polymer used in this work was 40%. Bending tests carried out for various radii of curvature demonstrated distinct sensor responses for positive and negative curvatures. The graphite nanobelt thin flexible films were successfully tested for acoustic vibration and heartbeat sensing.

Prussian Blue Analogues of Reduced Dimensionality

Mixed-valence polycyanides (Prussian Blue analogues) possess a rich palette of properties spanning from room-temperature ferromagnetism to zero thermal expansion, which can be tuned by chemical modifications or the application of external stimuli (temperature, pressure, light irradiation). While molecule-based materials can combine physical and chemical properties associated with molecular-scale building blocks, their successful integration into real devices depends primarily on higher-order properties such as crystal size, shape, morphology, and organization. Herein a study of a new reduced-dimensionality system based on Prussian Blue analogues (PBAs) is presented. The system is built up by means of a modified Langmuir-Blodgett technique, where the PBA is synthesized from precursors in a self-limited reaction on a clay mineral surface. The focus of this work is understanding the magnetic properties of the PBAs in different periodic, low-dimensional arrangements, and the influence of the "on surface" synthesis on the final properties and dimensionality of the system.

Photomagnetic Co–Fe Prussian Blue Thin Films Fabricated by the Modified Langmuir–Blodgett Technique

Abstract Co–Fe Prussian blue thin films have been prepared by means of a modified Langmuir–Blodgett technique, in which the hybrid monolayer composed of amphiphiles and clay platelets plays a template role for the formation Co–Fe Prussian blue thin films. Photoinduced magnetization was observed in the thin films as observed in the bulk Co–Fe Prussian blue. To the best of our knowledge, this is the first example of successful formation of Co–Fe Prussian blue thin films, which possess the ordered structure and, in addition, exhibit photoinduced magnetization.

Highly robust lipid membranes on crystalline S-layer supports investigated by electrochemical impedance spectroscopy

In the present work, S-layer supported lipid membranes formed by a modified Langmuir–Blodgett technique were investigated by electrochemical impedance spectroscopy (EIS). Basically two intermediate hydrophilic supports for phospholipid- (DPhyPC) and bipolar tetraetherlipid- (MPL from Thermoplasma acidophilum) membranes have been applied: First, the S-layer protein SbpA isolated from Bacillus sphaericus CCM 2177 recrystallized onto a gold electrode; and second, as a reference support, an S-layer ultrafiltration membrane (SUM), which consists of a microfiltration membrane (MFM) with deposited S-layer carrying cell wall fragments. The electrochemical properties and the stability of DPhyPC and MPL membranes were found to depend on the used support. The specific capacitances were 0.53 and 0.69 μF/cm 2 for DPhyPC bilayers and 0.75 and 0.77 μF/cm 2 for MPL monolayers resting on SbpA and SUM, respectively. Membrane resistances of up to 80 MΩ cm 2 were observed for DPhyPC bilayers on SbpA. In addition, membranes supported by SbpA exhibited a remarkable long-term robustness of up to 2 days. The membrane functionality could be demonstrated by reconstitution of membrane-active peptides such as valinomycin and alamethicin. The present results recommend S-layer-supported lipid membranes as promising structures for membrane protein-based biosensor technology.

Clay and a Zwitter Ionic Molecule Hybrid Film: Analysis of the Relationship between the Film Structure and the Conditions for Film Preparation

We have studied the relationship between the film structure and the conditions for film preparation of a hybrid film of a D- ~ -A zwitter ionic molecule and a sodium montmorillonite. The films were obtained by means of the modified Langmuir-Blodgett technique. As for the D- ~ -A zwitter ionic molecule, indoline-TCNQ intramolecular charge-transfer compound (ind-TCNQ) was employed. We have prepared various kinds of hybrid films by changing a parameter during the film preparation. The films thus obtained have been characterized by means of the second-harmonic generation measurements. As a result, a surface pressure at film deposition plays an important role for maintaining the film structure. clay sodium montmorillonite zwitter ionic molecule TCNQ derivative hybrid Langmuir-Blodgett film second-harmonic generation

Quasi one-dimensional gold cluster arrangements

Patterns consisting of 10 nm stripes of Au55(PPh3)12Cl6 clusters have been generated by degradation of two-dimensional, ordered cluster monolayers on a water surface. Applying a modified Langmuir–Blodgett technique stripe formation is induced by fast withdrawing (10 cm min−1) of a substrate, deposited underneath the monolayer, under an angle of 20°. The stripes, each consisting of 3–4 cluster rows, show a separation of 8 nm from each other. Slow transportation of the substrate (2–3 cm min−1) led to hexagonal patterns of crossing stripes. This effect is attributed to the existence of partially overlapping islands of monolayers.