Thin films of colloidal semiconductor CdSe quantum-dots (QDs) and a styrene/maleic anhydride copolymer were prepared by the Langmuir-Blodgett technique and their photoluminescence was characterized by confocal fluorescence lifetime microscopy. In the films, the photoluminescence dynamics are strongly affected by excitation energy migration between close-packed quantum-dots and energy trapping by surface-defective QDs or small clusters of aggregated QDs. Polymer/QD films with more aggregated QD regions exhibit lower PL intensities and faster decays, which we attribute primarily to the increased ability of excitations to find trap sites among more close-packed QD regions. This was confirmed by comparing films from bilayer or co-spreading deposition, and varying the QD-to-polymer composition or the surface pressure at deposition. The more regular films, such as those obtained by bilayer deposition at high-pressure, display more surface emission intensity and decays with less accentuated curvature. Decay analysis was performed with a model that accounts for excitation energy migration and trapping in the films. In the framework of the model, the photoluminescence dynamics are related to film morphology through the density of energy traps. A lower amount of QD clustering in the films reflects on a lower density of energy traps and, thus, on more emissive QD films, as inferred here for bilayer films relatively to co-spreading films.
Hybrid monolayers of clay minerals (hectorite) and Octadecyamine (ODA) were prepared using the Langmuir-Blodgett (LB) technique. Surface pressure-area per molecule isotherm, FTIR and atomic force microscopy were used to confirm and analyze the ODA-hectorite hybrid films. The monolayer thickness is 2 nm and average height, length and width of individual clay platelets ranges between 1.5 to 2 nm, 500 to 1250 nm and 100 to 115 nm respectively. The surface coverage was more than 80%.
This communication reports the formation of complex Langmuir monolayer at the air-water interface by charge transfer types of interaction with the water soluble N- cetyl N, N, N trimethyl ammonium bromide (CTAB) molecules doped with rosebengal (RB), with the stearic acid (SA) molecules of a preformed SA Langmuir monolayer. The reaction kinetics of the formation of RB-CTAB-SA complex monolayer was monitored by observing the increase in surface pressure with time while the barrier was kept fixed. Completion of interaction kinetics was confirmed by FTIR study. This complex Langmuir films at the a…
In this communication we investigate two dyes N,N' -dioctadecyl thiacyanine perchlorate (NK) and octadecyl rhodamine B chloride (RhB) in Langmuir and Langmuir-Blodgett (LB) films with or with out a synthetic clay laponite. Observed changes in isotherms of RhB in absence and presence of nano-clay platelets indicate the incorporation of clay platelets onto RhB-clay hybrid films. AFM image confirms the incorporation of clay in hybrid films. FRET was observed in clay dispersion and LB films with and without clay. Efficiency of energy transfer was maximum in LB films with clay.
Molecular electronics is a new, exciting and interdisciplinary field of research. The main concern of the subject is to exploit the organic materials in electronic and optoelectronic devices. On the other hand Langmuir-Blodgett (LB) film deposition technique is one of the best among few methods used to manipulate materials in molecular level. In this article LB film preparation technique has been discussed briefly with an emphasize of its application towards molecular electronics.
The Langmuir-Blodgett (LB) technique is a way of making supra-molecular assembly in ultrathin films with a controlled layered structure and crystal parameter, which have many envisioned technological applications for optical and molecular electronic devices as well as signal processing and transformation. Probably LB technique is the best method to manipulate materials at molecular level and provides a scope to realize the molecular electronics in reality. In this review article, this important film preparation has been discussed, highlighting its application potential.
Molecular aggregation and monolayer characteristics of non-amphiphilic p-terphenyl (TP) mixed with either polymethyl methacrylate (PMMA) or stearic acid (SA) at the air-water interface were investigated. The miscibility of the two components was evaluated by measuring and analyzing surface pressure versus area per molecule (pi-A) isotherm. Both attractive and repulsive interactions between the sample (TP) and the matrix (PMMA or SA) were observed depending on the composition and microenvironment. TP and PMMA/SA were not completely miscible in the mixed monolayer. Aggregation and phase separati…
This communication reports the -A isotherms and spectroscopic characterizations of mixed Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic 2, -biquinoline (BQ) molecules, mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). The pi-A isotherms and molefraction versus area per molecule studies indicate complete immiscibility of sample (BQ) and matrix (PMMA or SA) molecules. This immiscibility may lead to the formation of microcrystalline aggregates of BQ molecules in the mixed LB films. The scanning electron micrograph gives the visual evidence of microcrystalline aggregate…
The handling and manipulation of carbon nanotubes continues to be a challenge to those interested in the application potential of these promising materials. To this end, we have developed a method to deposit pure nanotube films over large flat areas on substrates of arbitrary composition. The method bears some resemblance to the Langmuir-Blodgett deposition method used to lay down thin organic layers. We show that this redeposition technique causes no major changes in the films' microstructure and that they retain the electronic properties of as-deposited film laid down on an alumina membrane.
Fractal-like nanopatterned DNA thin films have been fabricated on mica substrate by Langmuir-Blodgett (LB) technique. Structures and components of DNA nanopatterns were investigated using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of surface pressure on the transferred DNA composite films has been studied. Scanning force microscopic observations revealed that the surface structure and morphology of DNA nanopatterns can be well controlled by changing the surface pressure. The growth mechanism of the fractal-like nanopatterns is discussed in terms of the…
Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by peeling off and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solven…
A simple method is developed to synthesize gram quantities of uniform Ge nanowires (GeNWs) by chemical vapor deposition on preformed, monodispersed seed-particles loaded onto high surface area silica support. Various chemical functionalization schemes are investigated to passivate the GeNW surfaces using alkanethiols and alkyl Grignard reactions. The stability of functionalization against oxidation of germanium for various alkyl chain lengths is elucidated by X-ray photoelectron spectroscopy. Among all schemes tested, long chain alkanethiols (>=C12) are found to impart the most stable GeNW pas…
This paper reports the pi-A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir-Blodgett (LB) films of non-amphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). pi-A isotherm studies of mixed monolayer and as well as also the collapse pressure study of isotherms definitely conclude that CA is incorporated into PMMA and SA matrices. However CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates as is evidenced from the scanning electron micrograph picture. Nature of these aggregated species in the mixed LB…
Clay mineral particles are interesting nanosized building blocks due to their high aspect ratio and the chemical properties. The main interest in this nanosized building blocks results essentially from the colloidal size and the permanent structural charge of the particles. Smectites or swelling clay minerals are naturally occurring nanomaterials that can be fully delaminated to elementary clay mineral platelets in dilute aqueous dispersion. This dilute aqueous smectite suspensions are well suited to convert into functional nanofilms. The functionalization is performed by ion exchange reaction…
We report the magnetotransport properties up to 7 T in the organic highly conducting Langmuir-Blodgett(LB) films formed by a molecular association of the electroactive donor molecule bis(ethylendioxy)tetrathiafulvalene (BEDO-TTF) and stearic acid CH$_3$(CH$_2$)$_{16}$COOH. We show the logarithmic decrease of dc conductivity and the negative transverse magnetoresistance at low temperature. They are interpreted in the weak localization of two-dimensional (2D) electronic system based on the homogeneous conducting layer with the molecular size thickness of BEDO-TTF. The electronic length with phas…
The Langmuir-Blodgett technique was utilized and optimized to produce closed monolayers of cobalt-platinum nanoparticles over vast areas. It is shown that sample preparation, "dipping angle", and subphase type have a strong impact on the quality of the produced films. The amount of ligands on the nanoparticles surface must be minimized, the dipping angle must be around 105$^{\circ}$, while the glycol subphase is necessary to obtain nanoparticle monolayers. The achieved films were characterized by scanning electron microscopy (SEM) and grazing incidence x-ray scattering (GISAXS). The electrical…
Single walled carbon nanotubes exhibit advanced electrical and surface properties useful for high performance nanoelectronics. Important to future manufacturing of nanotube circuits is large scale assembly of SWNTs into aligned forms. Despite progress in assembly and oriented synthesis, pristine SWNTs in aligned and close-packed form remain elusive and needed for high current, speed and density devices through collective operations of parallel SWNTs. Here, we develop a Langmuir Blodgett method achieving monolayers of aligned SWNTs with dense packing, central to which is a non covalent polymer …
A plethora of different morphologies are fabricated by the self assembly of molybdenum disulphide (MoS2) exfoliated flakes with the help of Langmuir-Blodgett (LB) technique at the liquid/air interface. The MoS2 flakes are chemically exfoliated in various solvents but their stable sheet like assembly on substrate is achieved only in case of the flakes exfoliated in dimethylformamide. The density of the monolayer sheets is finely controlled by the surface pressure while the stabilization of MoS2 LB film onto the water subphase results in its self assembly into diffusion limited cluster aggregate…
We have fabricated layered nanocomposite consisting of a nanoporous anodic alumina sublayer (AOA), an ultrathin metal-containing polymer Langmuir-Blodgett (LB) film coating AOA, and multi-walled carbon nanotube (MCNT) - bundles which are arranged on the LB-film. MCNTs were preliminarily chemically modified by carboxyl groups and functionalized by stearic acid. We have experimentally observed an enhancement of Raman light scattering on surface plasmons in the LB-monolayers. This enhancement is due to charge and energy transfer. We demonstrate that propidium iodide (PI) fluorescence is quenched …
Although a considerable number of solvent based methodologies have been developed for exfoliating black phosphorus, so far there are no reports on controlled organization of these exfoliated nanosheets on substrates. Here, for the first time to the best of our knowledge, a mixture of N-Methyl-2-pyrrolidone (NMP) and deoxygenated water is employed as a subphase in Langmuir Blodgett (LB) trough for assembling the nanosheets followed by their deposition on substrates and studied its field effect transistor (FET) characteristics. Electron microscopy reveals the presence of densely aligned, crystal…
Langmuir-Blodgett (LB) films of dialkyldithiophosphate (DDP) modified Cu nanoparticles were prepared. The structure, microfrictional behaviors and adhesion of the LB films were investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic/friction force microscopy (AFM/FFM). Our results showed that the modified Cu nanoparticles have a typical core-shell structure and fine film-forming ability. The images of AFM/FFM showed that LB films of modified Cu nanoparticles were composed of many nanoparticles arranged closely and orderly and the nanoparticles …
Here we report the design and synthesis of an imidazole derivative namely 1-benzyl-2,4,5-triaryl imidazole and its switching behaviour assembled onto Langmuir-Blodgett films. Monolayer characteristic of imidazole at the air-water interface has been studied by surface pressure vs area per molecule isotherm, hysteresis analysis and insitu Brewster Angle Microscopy . These studies indicated the formation of stable floating Langmuir film at the water subphase. Atomic Force Microscopy investigation confirmed the successful deposition of the Langmuir film onto solid substrate. Device consisted of 60…
From Molecular Design to Optical Anisotropy: Orientation Control in BODIPY Langmuir-Blodgett Films
Service de Physique de l’État condensé (SPEC) Université Paris-Saclay, CEA-CNRS（凝聚态物理服务处（SPEC）巴黎萨克雷大学，CEA-CNRS）；Institut Lavoisier de Versailles (ILV) Université Paris-Saclay, UVSQ, CNRS（凡尔赛拉瓦锡研究所（ILV）巴黎萨克雷大学，凡尔赛大学，CNRS）
The behavior of ferroelectricity at the nanoscale is the focus of increasing research activity because of intense interest in the fundamental nature of spontaneous order in condensed-matter systems and because of the many practical applications of ferroelectric thin films to, for example, electromechanical transducers, infrared imaging sensors, and nonvolatile random-access memories. Ferroelectricity, in analogy with its namesake ferromagnetism, is the property of some crystalline systems to maintain a permanent, but reversible, electrical polarization in the absence of an external electric fi…
A novel stearic acid (SA)/3-aminopropyltrethoxysilane (APS) composite structure was fabricated using the combined method of the Langmuir-Blodgett technique and self-assembly monolayer (SAM) technique. Its frictional, adhesive properties and interface contact types between the atomic force microscope tip and the samples were evaluated based on Amonton's laws and the general Carpick's transition equation, respectively. The results showed that the tip-sample contacts corresponded to the Johnson-Kendall-Robert/Derjaguin-Muller-Toporov (DMT) transition model for SiO2, APS-SAMs, and the unheated SA-…
Langmuir-Blodgett (LB) films of N,N'-dioctadecyl thiacyanine perchlorate (NK) and octadecyl rhodamine B chloride (RhB18) and their mixtures in the presence and absence of clay mineral layers were investigated by recording surface pressure - area isotherms and by UV-Vis and fluorescence spectroscopies. The isotherms of NK, RhB18 and their mixtures are characteristic for liquid expanded state behaviour with repulsive interactions between the two cationic dyes. In the presence of laponite the isotherms show liquid expanded and condensed state behaviour. In laponite dispersions and in monolayers, …
Here we report the monolayer characteristics of a biodegradable polymer chitosan using Langmuir-Blodgett film technique. Usually chitosan has not form stable monolayer film. However they form stable monolayer film when mixed with fatty acid. Our result may be useful for the biological application of chitosan mainly in drug delivery. Since, the stability during the time of drug delivery is one of the important criteria for the choice of biomaterials suitable for forming the carrier film matrix and the barrier films.
In the present communication we report the preparation and characterizations of Langmuir and Langmuir-Blodgett films of a thiacyanine dye-dioctadecyl thiacyanine perchlorate (NK) mixed with Octadecyl trimethyl ammonium bromide (OTAB). The relationship between the molar ratio of OTAB and NK and the orientation of molecules at the air-water interface was investigated using surface pressure - area per molecule (π-A) isotherm. UV-Vis absorption and fluorescence spectroscopic investigations reveal that prominent J-aggregation of NK molecule was observed in the LB films lifted at higher surface pres…
Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic 2-(4-Biphenylyl)-5 phenyl-1,3,4- oxadiazole (abbreviated as PBD) mixed with stearic acid (SA) as well as also with the inert polymer matrix poly(methyl methacrylate) (PMMA) have been studied. Surface pressure versus area per molecule (-A) isotherms studies suggest that PBD molecules very likely stand vertically on the air-water interface and this arrangement allows the PBD molecules to form stacks and remain sandwiched between SA/PMMA molecules. At lower surface pressure phase separation between PBD and matrix molecules occur resultin…
We demonstrate that by means of a local top-gate current oscillations can be observed in extended, monolayered films assembled from monodisperse metal nanocrystals -- realizing transistor function. The oscillations in this metal-based system are due to the occurrence of a Coulomb energy gap in the nanocrystals which is tunable via the nanocrystal size. The nanocrystal assembly by the Langmuir-Blodgett method yields homogeneous monolayered films over vast areas. The dielectric oxide layer protects the metal nanocrystal field-effect transistors from oxidation and leads to stable function for mon…
According to Moore law, the silicon semiconductor transistor based information system is facing its physical limitations due to fluctuations of random charge and leakage current. Molecular electronics is becoming more and more attractive owing to the advantages of easy molecular structure variability, flexibility, low-cost and compatibility with bioelectronics. In this handbook chapter, we reviewed the recent research progress of molecular electronics, especially the studies on nanoscale information memories, from the viewpoints of structure-property relationship. Two kinds of molecular system…
A versatile X-ray/neutron reflectivity (specular) simulator using LabVIEW(National Instruments Corp.) for structural study of a multi-layer thin film having any combination, including the repetitions, of nano-scale layers of different materials is presented here (available to download from the link provided at the end of the paper). Inclusion of absorption of individual layers, inter-layer roughnesses, background counts, beam width, instrumental resolution and footprint effect due to finite size of the sample makes the simulated reflectivity close to practical one. The effect of multiple refle…
Liquid phase exfoliation followed by Langmuir-Blodgett self-assembly (LBSA) is a promising method for scalable production of thin graphene films for transparent conductor applications. However, monolayer assembly into thin films often induces a high density of defects, resulting in a large sheet resistance that hinders practical use. We introduce UV/ozone as a novel photochemical treatment that reduces sheet resistance of LBSA graphene threefold, while preserving the high optical transparency. The effect of such treatment on our films is opposite to the effect it has on mechanically exfoliated…
