Microcrystalline domains of monolayer and multilayer BDN-SA Langmuir–Blodgett films

Monolayer and multilayer BDN(Bis(4-diethyannodithiobenzil)nickel)-SA(stearyl alcohol) LB (Langmuir–Blodgett) films were prepared and the characteristics of microcrystalline domains were studied using UV–vis.–NIR and AFM. The results indicate that BDN-SA LB films consist of numerous ball-like microcrystalline domains at size scales from a few tens to a few hundreds of nm. AFM images of a multilayer LB film show that well-ordered molecular arrangements exist on the surface of domains which resemble a mosaic structure. The relationship between the mean size of the domain of a BDN-SA LB film with the thickness of the film was also shown.     

Formation and tribological properties of composite Langmuir–Blodgett films of stearic acid with molybdenum disulfide and amorphous carbon

The morphology and tribological properties of Langmuir–Blodgett mono- and bilayers of stearic acid with particles of molybdenum disulfide (MoS₂) and amorphous carbon (С), prepared on silicon and steel substrates by horizontal deposition (stearic acid–MoS₂ and stearic acid–С monolayers) and by the “roll” technique (stearic acid–MoS₂/stearic acid–С bilayers), were studied. Incorporation of C and MoS₂ particles into the structure of a stearic acid film enhances its wear resistance by a factor of 2.8 and 5.5, respectively. The presence of MoS₂ and С particles and of their aggregates of size from ~220 nm to 16.3 μm in stearic acid layers was confirmed by atomic force microscopy.     

Langmuir–Blodgett films of octadecanethiol on gold sols subphase

An octadecanethiol monolayer was formed on an aqueous gold sols subphase, it’s LB films were characterized by means of π-A isotherms, TEM (transmission electron microscopy), XRD (X-ray diffraction) and UV–Vis spectroscopy.     

Composite Langmuir–Blodgett (LB) films of polyaniline and cadmium stearate

Composite monolayers of cadmium stearate and polyaniline processed with camphor sulphonic acid have been obtained at the air–water interface and subsequently transferred onto substrates as uniform Langmuir–Blodgett multilayers. Pressure–area (Π-A) isotherm studies indicated that polyaniline molecules are not squeezed out of the cadmium stearate matrix during compression or in the compressed state. Monolayer stability is seen to decrease when the polymer content is increased beyond 60% (in weight) which is probably associated with the formation of microaggregates that also affected the monolayer surface potential at large areas per molecule. With increasing amount of polyaniline in the mixture, a transition from Y-type to Z-type deposition has been observed. Transferred multilayer LB films were characterized by UV-vis, FTIR, XRD, surface potential, and dc electrical conductivity measurements. UV-vis results indicated that though the polyaniline was in the doped state in the spreading solution, the transferred films were in the emeraldine base state. FTIR studies revealed that the transferred films mainly contained cadmium stearate salt in addition to polyaniline. XRD results indicated that the stacking order is dependent on the polyaniline content in the composite films, the order was found to decrease upon increasing the polymer amount. The uniformity of transferred films was confirmed by surface potential studies. A possible packing arrangement in these composite Langmuir and Langmuir–Blodgett films has been proposed.     

Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

Synthesis and photoreaction of Schiff bases derived from p-nitro cinnamaldehyde and diamines in Langmuir and Langmuir–Blodgett films

Monolayers of Schiff bases derived from ethylene diamine and o-phenylene diamine with p-nitro cinnamaldehyde, (compounds 1 and 2) at air/water interface have been studied. Photolysis of 1 in chloroform solution undergoes cis–trans isomerization on irradiation of white light while compound 2 does not undergo isomerization under photolytic conditions. The photolysis of 1 and 2 in Langmuir–Blodgett films (LB films) transferred to quartz plates form dimers. The change in product distribution is attributed to the influence of bridging group of the cinnamaldehyde moieties, molecular configuration and mobility of the compounds in solution, solid state and the aggregation of molecules in monolayer assemblies.     

Nonradiative energy transfer in mixed Langmuir monolayers and Langmuir–Blodgett films of compounds of different chemical composition and structure

Russian Chemical Bulletin - The efficiency of the Förster resonance energy transfer (FRET) in a monolayer film containing the energy donor and energy acceptor fluorophores is low since the...     

Preparation and characterisation of monolayers and Langmuir–Blodgett films of liquid crystal mixed with cubic silsesquioxanes

Polyhedral oligomeric silesquioxanes (POSS) with eight polyether substituents were mixed with the liquid crystal (LC) 4-octyloxy-4′-cyanobiphenyl and spread at the air/water interface. The surface pressure-area and surface potential-area isotherms were recorded for different weight ratios of both components. The obtained results showed that POSS molecules had beneficial influence on LC monolayer improving its stability and rigidity. Moreover, it was found that some LC–POSS mixtures collapse reversibly and form multilayer films on the top of LC monolayer. On the other hand, interfacial dilatational and shear rheology indicated decrease of elasticity of the films after mixing. Brewster angle microscopy revealed multilayer structure of the condensed film and formation of net-like structures in the expanded film. These films were successfully transferred on solid substrates using the Langmuir–Blodgett technique. The scanning electron microscopy images confirmed the film deposition and formation of networks by POSS–LC mixtures. These findings may be useful in the fabrication of electronic devices based on LCs.     

Surface plasmon resonance research on photoinduced switch properties of liquid crystalline azobenzene polymer Langmuir–Blodgett films

We report a novel phenomenon of photoisomerization-induced switch properties in liquid crystalline azo-benzene polymer poly{2-hydroetheyl methacrylate}-co-{6-[4-(S-2-methyl-1-butyloxycarbonylphenylazo) phenoxy]hexyl methacrylate} Langmuir–Blodgett (LB) monolayers. These monolayers were deposited on gold film and irradiated with UV (360 nm) and blue (450 nm) light. The switch properties were investigated by the surface plasmon resonance (SPR) technique. A method called photoinduced patterning was used for the fabrication of a model molecular device. It has been found that the photoinduced process of writing and erasing in such devices can be repeated for tens of cycles.     

Effects of substrate on the melting behavior of Cd arachidate Langmuir–Blodgett films

Nineteen monolayered Cd arachidate films were deposited on float glass substrate coated with Si and Ni over-layers. Two layers have been chosen with very different surface free energies. Melting behavior of films were studied using variable temperature X-ray specular reflectivity and Fourier transform infrared spectroscopy measurements. In conformity with earlier studies, melting of the multilayer precede by a transition from distorted hexagonal to hexaticlike phase. However, the transition temperature to hexaticlike phase as well as the melting temperature depend significantly on the type of layer. Both the transition temperatures are higher for the multilayer deposited on Ni layer as compared to those for the film deposited on Si layer. These results can be understood in terms of different surface free energies of Ni and Si layers. Further, in case of Ni layer, transition to hexaticlike phase is relatively sharper. Even in the molten state there is a significant difference in the structure of the Cd arachidate film on two layers; packing density of molecules in molten state is lower in case of substrate with higher surface free energy. These results suggest that the surface free energy of substrate plays a significant role in melting behavior of Langmuir–Blodgett films.     

Effects of silver nanoparticles doping on morphology and luminescence behaviour of ferroelectric liquid crystals Langmuir–Blodgett films

We report the deposition of Langmuir–Blodgett (LB) thin films of low-weight dispersed composite systems of ferroelectric liquid crystals (FLCs)–functionalised silver (Ag) nanoparticles. Because of their amphiphilic nature the molecules form stable Langmuir monolayers, which were transferred to silicon substrates. We noticed that absorption wave numbers are present for each bond constituting FLC–nanoparticles composite system, ensuring a complete transfer of molecules from water sub-phase. XRD showed intense peaks at 2θ = 3.2° due to the layer structure of FLC molecules. We infer from the morphology of LB films that doping of nanoparticles do not provide any hindrance to SmC* layer structure of FLC molecules. The photoluminescence study indicates blue shift in emission spectra and peak intensity increases with Ag nanoparticles concentration.     

A multiscale structural study of nanoparticle films prepared by the Langmuir–Blodgett technique

Arrays of magnetic nanoparticles (NPs) represent a very interesting challenge toward the development of new devices for magnetic applications such as data storage and spintronic. The final properties of such assemblies depending essentially on the spatial arrangement of NPs, it is of first importance to investigate precisely their structure. Here, the structure of monolayer and multilayer films of magnetic iron oxide NPs assembled by the Langmuir–Blodgett (LB) technique has been studied by usual techniques such as SEM, AFM and ellipsometry and by a new and an easy to process enhanced optical technique: the Surface Enhancement Ellipsometry Contrast (SEEC) microscopy. This technique is based on the use of a new generation of microscope slides used as substrates which allow the strong enhancement of the sample contrast to a point where it becomes possible to visualize the structure of monolayer and multilayer films at the nanoscale with a conventional optical microscope. The SEEC microscopy is demonstrated to be complementary to usual characterization techniques to study the structure of NPs films, especially for films containing very small nanosized NPs which are more difficult to analyze by usual techniques. While the film structure is investigated with lateral resolution of microns, the layer thickness is analyzed at the nanoscale (with a precision of 0.3 nm) with a close fit to the experimental measurements on local (AFM) and on larger (ellipsometry) areas. This technique presents the advantage to visualize directly the topography of NPs assemblies on very large areas by extracting information such as the height profile, the film roughness and generating 3D images.     

An infrared study on Langmuir–Blodgett films of octadecylammonium octadecanoate: FWHM and the vibrational coupling

The monolayer of the mixture of octadecanoic acid and octadecylamine with molar ratio 1:1 has been investigated at the air–water interface. It was found that the monolayer shows a rather stable state at the surface pressure of 30 mN/m and this monolayer can be transferred onto a CaF₂ plate by Langmuir–Blodgett (LB) technique. The infrared spectra of LB films indicated that octadecylammonium octadecanoate is formed by an intermolecular proton exchange between adjacent carboxylic and aminic groups (COO⁻ and NH₃⁺). In three-layer LB film, the CH₂ scissoring mode of the long hydrocarbon chains of octadecylammonium octadecanoate shows a broad band feature at about 1468 cm⁻¹ while this vibrational mode of three-layer LB film of the mixture (1:1) of deuterated stearic acid and octadecylamine (octadecylammonium octadecanoate-d35, C₁₈H₃₇NH₃⁺C₁₇D₃₅COO⁻) only shows a narrow band. The broad feature of the CH₂ scissoring mode in octadecylammonium octadecanoate probably originates from the coupling between the chain of stearic acid and that of octadecylamine while this kind of coupling could be completely removed in octadecylammonium octadecanoate-d35. Another conclusion presented in this paper is that there are no couplings among the chains of fatty acid or among the chains of octadecylamine in LB films of octadecylammonium octadecanoate.     

Monolayers and Langmuir–Blodgett films of amphiphilic tetramethylsulphonatocalix[4]resorcinarene and their interactions with polyethyleneimine and caeruloplasmin

The paper deals with the surface films of amphiphilic tetramethylsulphonatocalixresorcinarene (R = C₁₁H₂₃) 1 insoluble in water but forms rigid stable non-collapsing films at the water–air interface. Compression isotherms were used to investigate the interactions of the macrocycle films with two polymers fed to the aqueous subphases: synthetic – polyethyleneimine (PEI) and natural – an oxidase enzyme caeruloplasmin (CP). The interactions of the surface films of 1 with these substrates are predominantly dictated by the nature of the macromolecules and not by macrocycle interactions with their individual fragments. CP having retained its globular structure was extracted in the layer of 1 and became the dominating component of the film. The synthetic macromolecule of PEI, six times lower in its weight than CP, did not affect the morphology of the interfacial film, involved in the interactions only with its hydrophilic part directed inside the water.     

A novel amphiphilic push-pull ferrocene derivative: Langmuir–Blodgett films and second-order optical nonlinearity

The Langmuir–Blodgett (LB) films built from the mixture of an amphiphilic push–pull ferrocene derivative (P) and behenic acid were investigated. Langmuir films of P diluted by behenic acid exhibit a very good cohesion and the mixed films can easily be transferred onto solid substrates. Linear dichroism UV-visible and IR spectroscopy measurements of the mixed LB multilayers confirm that the molecules (P) are oriented to the substrate. The nonlinear optical experiments on the mixed monolayer deposited on the CaF₂ slide showed that P displayed efficient optical second harmonic generation (SHG) with a molecular hyperpolarizability (β) as high as 6.0×10^-29 e.s.u.     

Improved optical and electrical properties of sol–gel-derived boron-doped zinc oxide thin films

Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films.     

Characterization of CdS nanoparticles formed and aggregated in stearic acid Langmuir–Blodgett films by atomic force microscopy

Alternate films, which are composed of stearic acid and CdS nanoparticles were synthesized by exposing Langmuir–Blodgett (LB) films of cadmium stearate (CdSt₂) to H₂S gas at a pressure of 1 Torr. The changes of surface morphology of film with the increased reaction time were directly observed by atomic force microscopy for the first time. Before being exposed to H₂S, the surface of CdSt₂ LB film was homogeneous from microscale down to nanoscale, and it was observed that CdSt₂ molecules formed a well orderly rectangular herringbone lattice structure on the molecular scale. However, after being exposed to H₂S the ordered CdSt₂ molecules gradually changed into a disordered state, and eventually the LB film surface became rough with the apparent feature of bulk structures on the nanoscale. This change in the morphology can be attributed to the aggregation of buried CdS nanoparticles within LB films, which has been confirmed by a structured UV–visible absorption spectrum where the absorption edge is red-shifted about 0.7 eV with respect to bulk CdS. Finally, the aggregation mechanism of CdS in the LB film was analyzed.     

Preparation,characterization and electrochemical properties of Nafion® doped poly(ortho-anisidine) Langmuir–Schaefer films

Langmuir–Schaefer (LS) films of poly(ortho-anisidine) (POAS) were fabricated by utilizing water and water acidified HCl as subphases, respectively. The uniformity of the films formation and the doping with Nafion were verified by UV–Vis spectroscopy. The morphology and the thickness of the POAS, HCl post-doping POAS and Nafion post-doping POAS LS films were investigated using atomic force microscopy. The electrochemical properties of POAS LS films, HCl post-doping POAS and Nafion post-doping POAS were investigated and compared with our previously published work. The electrochemical switching time of HCl post-doping POAS and Nafion post-doping POAS LS films were also estimated.