Langmuir-Schaefer Method Research Articles

Сравнение политиофеновых мемристорных устройств, изготовленных послойным и центрифужным нанесением

Проведено сравнение основных характеристик мемристорных элементов на основе политиофена, изготовленных методами Ленгмюра–Шефера и центрифужного нанесения (спин-коатинга). Продемонстрирована стабильность элементов на протяжении более 500 циклов электрической перезаписи для обоих методов. Показано, что элементы, изготовленные методом спин-коатинга, обладают более медленной кинетикой переключения, что, предположительно, связано с относительно более высокой однородностью поверхности пленки. Данное исследование может быть полезно для разработки политиофеновых мемристорных элементов с воспроизводимыми стабильными характеристиками, пригодными для различных применений: от элементов памяти до носимой и имплантируемой электроники и нейроморфных вычислительных систем.

Study of xylan and cellulose interactions monitored with solid-state NMR and QCM-D

Abstract Development of physical properties of bleached eucalyptus kraft pulp is typically based on the refining process. However, many studies have reported that xylan deposition is a viable alternative. As the mechanisms of xylan and cellulose interactions are not clear, the main goal of this study was to achieve a better understanding of these interactions. Considering that a sample of pulp enriched with xylan is a very complex matrix, a model system was developed. Cellulosic thin films were prepared by spincoating and the Langmuir-Schaefer (LS) method from trimethylsilylcellulose (TMSC). Their interactions with xylan were analyzed using the quartz crystal microbalance with dissipation (QCM-D) monitoring technique. The topological changes on cellulose were studied using atomic force microscopy (AFM). For the 13C solid-state nuclear magnetic resonance (NMR) studies, samples were prepared using commercial microcrystalline cellulose (MCC) and xylan. The xylan was extracted from bleached birch kraft pulp using a cold caustic extraction (CCE) method. The QCM-D monitoring showed deposition only with higher concentrations of xylan solution (1 mg · l−1) for the LS method. The AFM images showed that xylan deposits as agglomerates on the cellulose surface, and the NMR experiments showed that there are interactions for the more ordered region of the cellulose fiber and for the less-ordered region.

Efficient Conversion of Photon Energy in Film Structures of Photoactive Molecules

Donor-acceptor dyad monolayers with opposite molecule orientations are grown using the Langmuir-Blodgett and Langmuir-Schaefer methods. The effect of the ‘built-in’ potential on photovoltaic responses of samples is shown. The directed charge transfer is studied during pulsed optical excitation in structures containing dyad, phthalocyanine, and polymer. The relative sensitivity of structures upon light absorption reaches 240 V·cm2 ·mJ−1.

Cellulose Nano-Films as Bio-Interfaces.

Cellulose, the most abundant polymer on earth, has enormous potential in developing bio-friendly, and sustainable technological products. In particular, cellulose films of nanoscale thickness (1–100 nm) are transparent, smooth (roughness <1 nm), and provide a large surface area interface for biomolecules immobilization and interactions. These attractive film properties create many possibilities for both fundamental studies and applications, especially in the biomedical field. The three liable—OH groups on the monomeric unit of the cellulose chain provide schemes to chemically modify the cellulose interface and engineer its properties. Here, the cellulose thin film serves as a substrate for biomolecules interactions and acts as a support for bio-diagnostics. This review focuses on the challenges and opportunities provided by engineering cellulose thin films for controlling biomolecules interactions. The first part reviews the methods for preparing cellulose thin films. These are by dispersing or dissolving pure cellulose or cellulose derivatives in a solvent to coat a substrate using the spin coating, Langmuir-Blodgett, or Langmuir-Schaefer method. It is shown how different cellulose sources, preparation, and coating methods and substrate surface pre-treatment affect the film thickness, roughness, morphology, crystallinity, swelling in water, and homogeneity. The second part analyses the bio-macromolecules interactions with the cellulose thin film interfaces. Biomolecules, such as antibodies and enzymes, are adsorbed at the cellulose-liquid interface, and analyzed dry and wet. This highlights the effect of film surface morphology, thickness, crystallinity, water intake capacity, and surface pre-treatment on biomolecule adsorption, conformation, coverage, longevity, and activity. Advance characterization of cellulose thin film interface morphology and adsorbed biomolecules interactions are next reviewed. X-ray and neutron scattering/reflectivity combined with atomic force microscopy (AFM), quartz crystal microbalance (QCM), microscopy, and ellipsometer allow visualizing, and quantifying the structural morphology of cellulose-biomolecule interphase and the respective biomolecules conformations, kinetics, and sorption mechanisms. This review provides a novel insight on the advantages and challenges of engineering cellulose thin films for biomedical applications. This is to foster the exploration at the molecular level of the interaction mechanisms between a cellulose interface and adsorbed biomolecules with respect to adsorbed molecules morphology, surface coverage, and quantity. This knowledge is to engineer a novel generation of efficient and functional biomedical devices.

Comparison of Polythophene Memistor Devices Manufactured by Layering and Centrifugal Methods

The main characteristics of memristive elements based on polythiophene made by Langmuir-Schaefer and spin-coating methods have been compared. The stability of the elements for more than 500 cycles of electric rewriting for both methods has been demonstrated. It has been shown that the elements made by spin-coating method have slower switching kinetics, which, presumably, is associated with relatively higher homogeneity of the film surface. This research may be useful for the development of polythiophene memristive devices with reproducible stable characteristics suitable for various applications: from memory elements to wearable and implantable electronics, and neuromorphic computing systems.

A graphene-based hybrid material with quantum bits prepared by the double Langmuir-Schaefer method.

The scalability and stability of molecular qubits deposited on surfaces is a crucial step for incorporating them into upcoming electronic devices. Herein, we report on the preparation and characterisation of a molecular quantum bit, copper(ii)dibenzoylmethane [Cu(dbm)2], deposited by a modified Langmuir–Schaefer (LS) technique onto a graphene-based substrate. A double LS deposition was used for the preparation of a few-layer-graphene (FLG) on a Si/SiO2 substrate with subsequent deposition of the molecules. Magnetic properties were probed by high-frequency electron spin resonance (HF-ESR) spectroscopy and found maintained after deposition. Additional spectroscopic and imaging techniques, such as Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were performed to characterise the deposited sample. Our approach demonstrated the possibility to utilise a controlled wet-chemistry protocol to prepare an array of potential quantum bits on a disordered graphene-based substrate. The deployed spectroscopic techniques showed unambiguously the robustness of our studied system with a potential to fabricate large-scale, intact, and stable quantum bits.

Fabrication of Multilayer Films on the Basis of Lysozyme Protein and Precipitant (Iodide and Potassium) Ions on a Silicon Substrate by the Modified Langmuir–Schaefer Method

Multilayer structures, consisting of successive lysozyme layers and layers of iodide and potassium ions, have been formed on a silicon substrate by the modified Langmuir–Schaefer method; the use of this technique implies preliminary preparation of a crystallization protein solution containing an oligomeric phase. The multilayer structure has been characterized by methods of X-ray reflectivity and total external reflection X-ray standing waves (TER XSW). The data obtained indicate the formation of a dense lysozyme film (3 nm thick) and layers of potassium and iodide ions, adjacent to this film.

High ability of a blue phase polymer based on a diacetylene alcohol derivative

The effect of prolonged UV irradiation and high temperature on a blue phase polymer film prepared by the Langmuir–Schaefer method based on 11-hydroxyundeca-6,8-diyn-1-yl N-(4-methoxyphenyl)carbamate was evaluated. The high stability of the polymer under extreme external influences was revealed. The transition of a monolayer to a bilayer with increasing surface pressure during the Langmuir layer formation was confirmed by atomic force microscopy.

Characterization of floating-gate memory device with thiolate-protected gold and gold-palladium nanoclusters

The floating-gate memory characteristics of thiolate-protected gold (Au:SR) and palladium doped Au (AuPd:SR) nanoclusters, Au25(SR)18, Au24Pd(SR)18, and Au38(SR)24 (R = C12H25), were investigated by capacitance-voltage (C–V) measurements in vacuum. Monolayer films of Au:SR nanoclusters were formed as floating-gate memory layers on p-type Si substrates by the Langmuir-Schaefer method with surface pressure − area (π-A) isotherm measurements. A fluoropolymer (CYTOP, ∼15 nm thick) was spin-coated on top to form a hydrophobic insulating layer. Using an Au pad (∼40 nm thick) as the gate electrode, C–V measurements exhibit clockwise hysteresis curves originating from the Au:SR and AuPd:SR nanoclusters against the reference measured in each sample, and the hysteresis widths were dependent on the composition and sizes of the Au:SR nanoclusters. The positive and negative voltage shifts in the hysteresis can be explained in terms of electronic structures in Au:SR and AuPd:SR-based devices.

Probing Device Degradation and Electric Fields in Polymeric Field-Effect Transistors by SFG Vibrational Spectroscopy

There is great interest on the study of the semiconductor/dielectric interface of organic field-effect transistors (OFETs), where a conducting channel is formed. Here, we use the interface selectivity, chemical sensitivity, and field-induced enhancement of sum-frequency generation (SFG) vibrational spectroscopy to probe interfacial molecular ordering and degradation processes in poly-3-hexylthiophene (P3HT) OFETs and also the electric field within their dielectric layer (poly(methyl methacrylate), PMMA). P3HT active layers fabricated by the Langmuir–Schaefer method are more orientationally ordered than spin-coated films. Upon electrical degradation of the device in ambient conditions, no noticeable changes were detected in the SFG spectra of the semiconductor/dielectric interface because the sensitivity of our experiment was not enough to detect degraded polymer chains due to loss of SFG electronic resonance enhancement. Perhaps for the same reason, we were also not able to detect any significant changes ...

Controlled deposition of fullerene derivatives within a graphene template by means of a modified Langmuir-Schaefer method

The scientific and technological potential of graphene's includes the development of light, open 3D hybrid structures with high surface area, tunable pore size and aromatic functionalities. Towards this aim, we describe a scalable and low-cost bottom-up approach that combines self-assembly and Langmuir-Schaefer deposition for the production of fullerene-intercalated graphene oxide hybrids. This method uses graphene oxide (GO) nanosheets as template for the attachment of two types of fullerene derivatives (bromo-fullerenes, C60Br24 and fullerols, C60(OH)24) in a bi-dimensional arrangement, allowing a layer-by-layer growth with control at nanoscale. Our film preparation approach relies on a bottom-up process that includes the formation of a hybrid organo-graphene Langmuir film, which is transferred onto a substrate and then brought in contact with C60(OH)24 molecules in solution to induce self-assembly. In the case of grafting C60Br24 molecules into graphene a further modification of the GO platelets was performed by bringing the surface of the transferred GO Langmuir film in contact with a second amino surfactant solution. Repeating these deposition cycles, pillared structures were fabricated in thin films form. These fullerene-based hybrid thin films were characterized by Raman and X-ray photoelectron (XPS) spectroscopies, X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and contact angle measurements.

Pb arachidate Langmuir-Blodgett coatings of silicon wafers: relation between Pb particle density and subphase composition

The formation of lead arachidate (Pb(AA)2) coatings produced by Langmuir tensiometry (LT) was studied in dependence of lead nitrate (Pb(NO3)2) concentration in the aqueous subphase at pH 5.5. The stable Pb(AA)2 monolayers were transferred to Si wafers and TEM grids at 35 mN/m in the liquid condensed phase of the AA monolayer applying the Langmuir-Blodgett (LB) (ten monolayers) or the Langmuir-Schaefer (LS) technique, respectively. The most homogeneous monolayer was obtained at a Pb(NO3)2 concentration of 0.1 mM by using the LS method. Most homogeneous films (five bilayers) were obtained for a Pb(NO3)2 concentration of 0.01 mM by using the LB method. The formed films are investigated by transmission electron microscopy (monolayer produced by LS), X-ray reflectivity (XRR), and atomic force microscopy (films produced by LB). These methods revealed the formation of homogeneously distributed lead inclusions in the formed monolayers and films. Pb aggregates increase in number whereas their average size stays constant at ≈ 50 nm2 with increasing Pb(NO3)2 concentration. Thickness parameters were determined by XRR. With increasing Pb(NO3)2 concentration, the bilayer thickness was found to increase. Furthermore, the patterns (111) and (200) for a cubic lead structure were found. The experimental results are compared with simulations obtained from geometry optimization on a semi-empirical quantum level to discuss the lead-ion binding to the AA molecules at pH 5.5.

Stretchable composite monolayer electrodes for low voltage dielectric elastomer actuators

In this work, a Multiwalled Carbon Nanotube/poly(alkylthiophene) (MWCNT/PT) composite is developed as the electrodes for dielectric elastomer actuators (DEAs) using the Langmuir-Schaefer (LS) method. These composites form stable monolayers at the air-water interface that can then be LS transferred onto a poly(dimethylsiloxane) (PDMS) elastomer membrane. The monolayer electrode remains conductive up to 100% uniaxial strain. We present a method to fabricate DEAs using the LS transferred electrodes. By using a mask during the transfer step, the electrodes can be patterned with better than 200 μm resolution on both sides of a 1.4 μm-thick pre-stretched PDMS membrane to produce an ultra-low voltage DEA. The DEA generates 4.0% linear strain at an actuation voltage of 100 V, an order of magnitude lower than the typical DEA operating voltage.

Thermal stability of γ-Fe2O3 nanoparticles and their employment for sensing of acetone vapours

Stability of γ-Fe2O3 nanoparticles-based films upon an isochronal annealing in air was investigated by x-ray diffraction, differential scanning calorimetry, and thermogravimetry. The γ-α transformation temperature increased owing to the nanoscaling of Fe2O3; the higher stability of the γ phase was explained on the ground of the surface free energy of nanoparticles (with the size of about 6.4 nm). Further, chemiresistors based on the Fe2O3 nanoparticle bilayer prepared by the Langmuir-Schaefer method were fabricated and examined in terms of their sensitivity to acetone vapours down to 500 ppb concentration in air.

Homogenous Dispersion of MoS2 Nanosheets in Polyindole Matrix at Air-Water Interface Assisted by Langmuir Technique.

Two-dimensional (2D) inorganic layered materials when embedded in organic polymer matrix exhibit exotic properties that are grabbing contemporary attention for various applications. Here, nanosheet morphology of molybdenum disufide (MoS2) synthesized via one-pot facile hydrothermal reaction are exfoliated in benign aqueous medium in the presence of indole to obtain a stable dispersion. These exfoliated nanosheets then act as host to template the controlled polymerization of indole. The preassembled MoS2-polyindole (MoS2-PIn) nanostructures are reorganized at the air-water interface using the Langmuir method to facilitate maximum interfacial interaction between nanosheet and polymer. This report emphasizes large area, homogeneous dispersion of uniform-sized MoS2 nanosheets (40-60 nm diameter) in the PIn matrix and the formation of stable and uniform film via the Langmuir-Schaefer (LS) method. These self-assembled, MoS2 decorated PIn LS films are characterized using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The fabricated LS films in sandwiched structure Al/MoS2-PIn/ITO as the Schottky diode portrayed remarkable enhancements in charge transport properties. Our study illustrates the potential of the MoS2-PIn LS film in electronic applications and opens a new dimension for uniform dispersion of 2D materials in other polymers via the Langmuir method for device fabrication and enhancement of electrical properties.

Polarized neutron reflectometry study from iron oxide nanoparticles monolayer

We report on the polarized neutron reflectometry investigation of monolayer of magnetic iron oxide nanoparticles assembled by the Langmuir–Schaefer method. After deposition onto a solid substrate the polarized neutron reflectometry measurements in the external magnetic field were carried out. Thickness, density, roughness and in-depth resolved magnetization profile of the resulted layer were obtained from accurate fitting routine.

Modification of the Langmuir–Schaefer method for fabrication of ordered protein films

A modification of the Langmuir–Schaefer method for the fabrication of high-quality protein films on a solid substrate was proposed and applied to lysozyme. The procedure relies on the use of a pre-prepared protein solution, the parameters of which correspond to crystallization conditions. A lysozyme Langmuir monolayer was shown to be formed with the involvement of complexes, namely, dimers and octamers of protein molecules that are present in such protein solutions. These complexes apparently retain the structure after spreading a protein solution onto an aqueous subphase in a Langmuir trough. The thickness of the film after the transfer of the monolayer, which was formed by the proposed procedure, onto a solid substrate corresponds to the diameter of the octamer and this film is dense, continuous, and uniform, as was demonstrated by several methods: X-ray reflectivity, total external reflection X-ray standing wave, and atomic force microscopy. A layer of chloride ions that formed under the Langmuir monolayer was found at the air–protein film interface. This fact confirms an important role of the precipitating agent (chloride ions) in all steps of the formation of lysozyme films.

Diketopyrrolopyrrole‐Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

AbstractFunctional field‐effect transistors (FETs) have received increasing attention in recent years. Herein, it is demonstrated that the incorporation of hydrophilic tetraethylene glycol (TEEG) chains into the diketopyrrolopyrrole (DPP)‐based semiconducting polymer (PDPP3T1) can facilitate the formation of polymeric monolayer at the air–water interface, and the resulting field‐effect transistors (FETs) show sensitive and selective response toward alcohol vapor. By using the Langmuir–Schaefer method, monolayer and ultrathin films from bilayer to five‐layer can be successfully prepared. Interestingly, nanopores with sizes of 50–100 nm are formed within the monolayer film, as observed by using atomic force microscopy. The monolayer FET exhibits relatively high hole mobilities up to 0.014 cm2 V−1 s−1, which is among the highest charge mobilities reported for ultrathin film FETs prepared with the Langmuir technique. Moreover, hole mobility increases with an increase in the thickness of the ultrathin film from monolayer to three‐layer, and it reaches 0.04 cm2 V−1 s−1 for three‐layer FETs. A variation of both on‐current and off‐current is detected for monolayer FET upon exposure to alcohol vapor. The monolayer FET displays ultrahigh sensitivity (down to 1 ppb) and good selectivity toward alcohol vapors, in particular ethanol vapor. This can be attributed to the synergetic effects of the hydrophilic TEEG chains in PDPP3T1 and the nanopores within the monolayers.

Long-Term Cyclability of Electrochromic Poly(3-hexyl thiophene) Films Modified by Surfactant-Assisted Graphene Oxide Layers.

Organic electrochromic (EC) materials are generally known to be electrochemically unstable during the ion intercalation/deintercalation process. One effective method to stabilize them is incorporating graphene derivatives in the polymer matrix, thereby creating strong interaction between graphene derivatives and polymer. However, previous studies are limited to specific polymers and bulk-blended systems, such as mixing the polymer with graphene derivatives. In this study, we developed a polymer-graphene derivative complex with the chemical assistance of a surfactant (octadecylamine, ODA). Graphene oxide (GO) was introduced as a protective layer on the electrochromic poly(3-hexyl thiophene) (P3HT) films by the Langmuir-Schaefer method. The deposition of the GO-ODA protective layer with high coverage was confirmed by atomic force microscopy and high-resolution X-ray reflectivity. The strong interactions between GO-ODA and P3HT were examined with UV-vis spectrophotometry and X-ray photoelectron spectroscopy. Electrochemical and electrochromic investigations revealed that the GO-ODA layer greatly improved the long-term cyclability of the P3HT film. These findings imply that the GO-ODA complex can significantly stabilize the EC cycling, due to its strong interaction with the P3HT film.

Graphene/Carbon Dot Hybrid Thin Films Prepared by a Modified Langmuir-Schaefer Method.

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir–Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV–visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.