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Here we present the results on an investigation of resonant Stokes and anti- Stokes surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on arrays of Au nanoclusters using the Langmuir–Blodgett technology. The thickness of deposited NCs, determined by transmission and scanning electron microscopy, amounts to approximately 1 monolayer. Special attention is paid to the determination of the localized surface plasmon resonance (LSPR) energy in the arrays of Au nanoclusters as a function of the nanocluster size by means of micro-ellipsometry. SERS by optical phonons in CdSe NCs shows a significant enhancement factor with a maximal value of 2 × 103 which depends resonantly on the Au nanocluster size and thus on the LSPR energy. The deposition of CdSe NCs on the arrays of Au nanocluster dimers enabled us to study the polarization dependence of SERS. It was found that a maximal SERS signal is observed for the light polarization along the dimer axis. Finally, SERS by optical phonons was observed for CdSe NCs deposited on the structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates quasi-single NC Raman spectra being obtained.

Formation and assembling of CdS nanocrystals (NC) on highly-ordered pyrolytic graphite (HOPG) and on oxidized silicon substrates have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). NC were initially formed within a Langmuir-Blodgett (LB) matrix of cadmium behenate. The LB matrix was then removed by annealing in an ammonia atmosphere. It is shown that the NC self-assembling is mainly determined by the LB matrix wetting properties. In case of wettable HOPG substrate homogeneous matrix evaporation occurs that leads to coarsening of the NC arrays as the main self-assembly process. Otherwise, NC prepared on non-wettable SiO2-Si substrate demonstrate arrays formation determined by the LB matrix dewetting process. For the both cases, the influence of kinetic limitations connected with matrix evaporation rate on the self-assembly process is observed. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A method is proposed for the formation of ZnO nanoparticles (NP) in dimethylformamide, which permits variation of the mean NP diameter from 3.6-3.7 to 6.0 nm by selecting the suitable duration and temperature of the post-synthesis heat treatment. The ZnO nanoparticles in DMF display characteristic photoluminescence, emitting in a broad band with maximum at 2.24-2.25 eV, with a quantum yield up to 13%, and a mean radiative lifetime of ~2 μs. Giant enhancement of Raman scattering on the surface phonons of the ZnO NP is observed upon the photoexcitation of these NP with an island-like silver film deposited on their surface.

Here, we present the results on the investigation of structural and vibrational properties of CuxS (x = 1–2) nanocrystals formed using the Langmuir–Blodgett technique. The synthesis requires deposition of high quality Langmuir–Blodgett films of copper behenates on a solid substrate (Si, Au, and Pt). The Langmuir–Blodgett film is then sulfidized, what results in the formation of the copper sulfide nanocrystals embedded in behenic acid matrix. Finally, free-standing CuxS nanocrystals are obtained after temperature annealing at 120–400 °C in an Ar atmosphere. Morphology (size, shape, and areal density) and the crystal structure of nanocrystals were determined by direct structural methods including scanning and transmission electron microscopies and high-energy electron diffraction. Surface-enhanced Raman scattering (SERS) by optical phonons in CuxS nanocrystals in the vicinity of metal nanoclusters provided a significant enhancement factor (about 25) and allowed the fine structure of their phonon spectrum to...

The morphology and structure of CuS crystals formed during sulfidation of copper behenate films obtained by the Langmuir-Blodgett (LB) method have been studied using high resolution electron microscopy. The average size of these crystals is about 3 nm and increases by a factor of approximately 2.2 after annealing at a temperature of 150 °C or above. Analysis of interplanar distances has shown that in the range of annealing temperatures of 150–200 °C, CuS nanocrystals have a P63/mmc hexagonal crystal lattice with parameters a = 0.38 nm and c = 1.64 nm. At annealing temperatures of 250 °C or above, the Cu2S crystalline phase begins to form, in addition to CuS nanocrystals. The proportion of this phase increases with increasing annealing temperature. Cu2S nanocrystals have a hexagonal crystal lattice type with the P63/mmc spatial group and unit cell parameters a = 0.39 nm and c = 0.68 nm. Quantitative evaluation of copper and sulfur in individual CuS and Cu2S nanocrystals was performed by local analysis of characteristic X-ray spectra.

article i nfo This work is devoted to the investigation of surface-enhanced Raman scattering by vibrational modes of co- balt phthalocyanine ultrathin films and CuS nanocrystals prepared using by organic molecular beam vapor deposition and the Langmuir-Blodgett technique, respectively, on laterally ordered arrays of Au nanoclusters formed by electron beam lithography on Si and GaAs substrates. The surface-enhanced Raman scattering study of cobalt phthalocyanine films demonstrates the strong depen- dence of Raman intensity of vibrational modes in cobalt phthalocyanine on the laser excitation wavelength as well as on the size and period of Au nanoclusters. By tuning the optical resonance conditions a maximal en- hancement factor of 2 × 10 4 is achieved. The investigation of surface-enhanced Raman scattering by cobalt phthalocyanine deposited on laterally ordered arrays of paired Au nanoclusters (dimers) reveals anisotropic enhancement with respect to polarization of the scattered light parallel or perpendicular to the dimer axis. © 2013 Elsevier B.V. All rights reserved.

We present a study of resonant and surface enhanced Raman scattering by arrays of nanocrystals (cadmium sulfide CdS, lead selenide PbSe, and zinc oxide ZnO) with various areal density fabricated by using the Langmuir−Blodgett technique and colloidal chemistry. Resonant Raman scattering by transverse, longitudinal, and surface optical (TO, LO, and SO) phonons and their overtones up to ninth order was achieved for nanocrystal (NC) arrays by adjusting the laser energy to that of the interband transitions. The resonance enhancement allowed a Raman response from arrays of NCs with a low areal density (down to 10 PbSe NCs per 1 μm 2 ) to be measured. An enhancement of Raman scattering by LO and SO modes in CdS NC arrays with a low areal density by a factor of about 730 was achieved due to the resonant surface enhanced Raman scattering effect.

Forster resonance transfer of excitons from self-assembled InAs/AlAs quantum dots to cyanine dye molecules deposited on the structure surface is investigated. It is shown that the efficiency of the exciton transfer changes upon the interaction of cyanine dye molecules with chloroform due to a change in the molecule dipole moment.

Aggregation clusters of CdS quantum dots (QDs) on the highly ordered pyrolytic graphite substrate were investigated by atomic force microscopy and scanning tunneling microscopy. QDs were initially ...

The UV induced photopolymerization of Langmuir-Blodgett films of lead salt of 2-docosynoic acid (CH3(CH2)18C=CCOOH) is studied using IR and Raman spectroscopy. It is found that the films are a highly ordered system with trans-configuration of alkyl chains and a bridged complex generated between the carboxyl group and the lead ion. Based on a change in the absorption band intensity in the IR spectra corresponding to the triple bond vibration, the degree of polymerization depending on the irradiation time is determined. In the Raman spectra, a peak at ∼1635 cm−1 appears during polymerization, which corresponds to the C=C double bond. The formation of conjugated double bonds in these systems is observed for the first time. During polymerization, methylene chains of molecules retain trans-configuration; the structural ordering of molecules in the film is observed.

The 2-(4-hexadecylmethylamino)phenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide radical, which contains a long alkyl chain and a strong donor substituent conjugated with a nitronyl nitroxide group (an acceptor), was synthesized. The behavior of monolayers formed by this radical on a water surface and the conditions of their transfer onto solid substrates by the Langmuir-Blodgett method were examined. UV-VIS and IR spectroscopies, atomic force microscopy, and small-angle X-ray scattering were used to study the optical and structural characteristics of films prepared from the pure radical and its mixtures with behenic acid. It was revealed that radical aggregates are formed both in solutions and Langmuir-Blodgett films.

Langmuir-Blodgett films are prepared from lead, cadmium, and copper salts of carboxylic acids, namely, 23-tetracosynoic acid HC≡C(CH2)21COOH (with the terminal triple bond) and 2-docosynoic acid CH3(CH2)18C≡CCOOH (with the internal triple bond). The structural transformations in the films during polymerization under exposure to UV radiation are investigated using X-ray reflectomertry. It is found that the X-ray reflectograms of the initial films prepared from salts of both acids exhibit no less than four or five pronounced intense Bragg reflections. This suggests that the initial films have good layer ordering. The bilayer periods for all the films are determined, and the influence of the salt type on the bilayer period is analyzed. It is established that, under exposure to UV radiation, the structural transformations in the films prepared from the salts of 23-tetracosynoic acid occur without substantial disturbances and defects, as can be judged from the absence of significant changes in the location and intensity of the Bragg reflections. An increase in the time of irradiation of the films prepared from the salts of 2-docosynoic acid leads to an increase in the bilayer period. This effect is especially pronounced for the lead and copper salts. However, upon long-term exposure to UV radiation, the salts undergo photolysis, the bilayer period decreases, and the structure of the film begins to break down.

Structures with CdS, PbS, ZnS quantum dots (QDs) produced using the Langmuir–Blodgett technique were investigated by infrared (IR), Raman and ultra-violet–visible (UV–Vis) spectroscopies. The QDs size derived from the analysis of UV–Vis spectra and high-resolution transmission electron microscopy images amounts to 2–6 nm. The IR and Raman spectra reveal longitudinal optical phonons localised in QDs and surface vibrational modes. The frequency positions of the surface optical vibrational modes are adequately described taking into account confinement of fundamental optical phonons in the QDs.

Structures with CdS quantum dots produced by the Langmuir–Blodgett (LB) technique were investigated by Raman, IR, and UV spectroscopies. The confinement effect of longitudinal optical (LO) phonons in CdS quantum dots was investigated by Raman spectroscopy. Surface vibrational modes of CdS quantum dots were observed in IR spectra. It was shown experimentally that the frequency of the surface vibrational modes depends on the properties of the surrounding media. An average size of CdS quantum dots of about 3–6.4 nm was obtained from the analysis of UV measurements.

The wet etching behavior of CoSi 2 films in HF-based solutions is investigated for a wide range of experimental conditions. It is established that the etching rate of CoSi 2 depends on the concentrations of H + ions and on the initial concentration of HF ([HF],). Interaction of H + and HF with the CoSi 2 occurs in the adsorption layer. The concentration of adsorbed particles is described by the equation of the Freundlich adsorption isotherm. The kinetic equation of the etching rate is R = k R Θ H .Θ HF , where k R 2.5. 10 7 exp (-10500/RT) nm/s (0.416 at 293 K), Θ H . [H + ] 0.135 and Θ HF [HF] 1 0.310 . It is shown that the induction period increases in the etching process of CoSi 2 in diluted HF 1 which is attributed to the presence of a thin surface layer on top of the CoSi 2 .

Acyl derivatives of 2-aminopyridine, 2-aminopyrimidine, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl were obtained from long-chain diacetylenic acyl chlorides and the corresponding heterocyclic compounds. Spreading isotherms of monolayers on a water surface show that lengthening of the hydrocarbon chain and replacement of the pyridyl groups in these compounds by the more hydrophilic pyrimidyl groups render the films more condensed. Long-chain acyl derivatives of nitroxyl radicals form monolayers possesing a low collapse pressure. ESR spectra of Langmuir-Blodgett films of these radicals before and after photopolymerization were recorded.

Thermodesorption processes of mono-and multilayers of fatty acids and their salts with 14 to 24 carbon atoms were investigated by ellipsometry and IR spectroscopy. Cadmium, calcium, strontium, and barium salt layers, unlike the layers of pure acids, have a complex phase composition which includes not only separate acid and salt phases, but also intermediate acid-salt forms. The initial phase composition of multilayer systems determines their thermodesorption spectrum observed upon heating the samples. It was found that before the removal of molecules to the gaseous phase, phase transitions are possible in the films, similar to those observed in crystals and caused by the change of molecular conformations in the layer. Energy characteristics of thermodesorption processes are estimated for pure acid layers and for separate phases in salt layers. Possible qualitative models of the processes are discussed.

The structure of Langmuir-Blodgett (LB) diacetylene films CH3‒(CH2)11‒C≡C‒C≡C‒(CH2)8‒COOCd1/2 (DA1) and CH3‒(CH2)20‒CO2‒CH2‒C≡C‒C≡CH2OH (DA2) was studied by X-ray small angle scattering and electron diffraction methods prior to and upon their polymerization. It has been established that Langmuir films have layer packing. The periods of the constituent layers were determined as 58 A (for DA1) and 69 A (for DA2). This indicates the existence of a vertical bilayered packing of molecules. It has also been established that polymerization of LB diacetylene films due to the action of UV irradiation does not change the layer thickness appreciably and the structural rearrangement reduces to a slight redistribution of the electron density along the molecules which is explained by a break of the triple bonds during the UV irradiation.

Clustering of CdS nanocrystals during evaporation of the Langmure—Blodgett matrix and influence of matrix thickness on the parameters of the resulting clusters have been investigated. Information about the size and spatial distribution of nanocrystals and clusters has been obtained using atomic-force microscopy. It has been found that at thickness of the matrix less than 6 nm the free-standing nanocrystals are formed; with increase in thickness of the matrix nanocrystals are collected in clusters. The clusters greatly enlarge with further increase in thickness of the matrix, eventually; at thickness of 60 nm nanocrystals totally coat the substrate.

Surface enhanced Raman scattering is studied in nanostructures with GaN and ZnO nanocolumns. Features related to optical phonons of nanocolumns are observed in the Raman spectra of both free-standing GaN and ZnO nanostructures. Strong enhancement of the Raman scattering intensity by surface optical phonons in GaN and ZnO nanocolumns is observed by deposition of silver clusters onto the nanostructure surfaces.

For dipalmitoylphosphatidylcholine (DPPC) lipid/water bilayers, a detailed temperature dependence of the Raman scattering spectra at the spectral range of the CH 2-stretching modes was investigated. Below 150 K the ratio of intensities of the 2880 cm (-1) antisymmetric vibration line and the 2850 cm (-1) symmetric one was found to be nearly temperature-independent. Between 150 and 230 K it decreases slightly as temperature increases; and above 230 K it decreases remarkably. This decrease is accompanied with broadening of the antisymmetric line, from 4.2 cm (-1) at 100 K to 5.7 cm (-1) at 296 K. According to literature, the decrease of the antisymmetric line may be interpreted in two ways: (i) the appearance of a static conformational disorder (or of a disorder fluctuating at the time scale larger than picoseconds) and (ii) relaxation at the ps time scale, which is induced by coupling with temperature-activated librational-torsional motion of the lipid chain. Both these interpretations imply that obtained data evidence the appearance of molecular flexibility of lipids around approximately 200 K. The observed effect is to be compared with low-temperature dynamical transition found in disordered media with neutron scattering, Mossbauer absorption, molecular dynamics simulations and other techniques. This transition implies that with temperature increase harmonic atomic motions are transformed to large-amplitude anharmonic (or stochastic) ones. The characteristic times of these motions lay at the ps time scale. The closeness of the temperature of the transition and of the time scale of motions with those found in this work by Raman scattering for lipid bilayers supports the dynamic nature of the 2880 cm (-1) antisymmetric vibration line decrease (i.e., that it is induced by coupling with libration-torsion). To prove that the observed onset of flexibility is a property of a disordered state, Langmuir-Blodgett films of behenic acid were studied. These films contain, like lipids, long CH 2-tails, but, in opposite to bilayers, they have a well-ordered crystalline-like structure. The relative intensity of the antisymmetric/symmetric CH 2-stretching lines was found in these films to be temperature-independent in the whole temperature range studied, between 60 and 296 K.

Photoluminescence (PL) from CdS nanoclusters formed in the matrix of a Langmuir-Blodgett film and from the same clusters with the matrix removed has been studied. The PL spectrum of clusters in the matrix has the form of a broad band (full width at half-maximum (FWHM) ∼ 0.6 eV) peaked at 2.4 eV. After removing the matrix with hexane, the PL spectrum consists of a high-energy band at 2.9 eV (FWHM ∼ 0.2 eV) and two low-energy bands at 2.4 and 2.0 eV (FWHM ∼ 0.5 eV). The high-energy band is attributed to exciton recombination in the nanoclusters, and the bands at 2.4 and 2.0 eV, to recombination via levels related to defects in the bulk of the matrix and at the nanocluster-matrix interface, respectively.

The adsorption of SO2 on thin Langmuir–Blodgett layers of long-chain molecules containing tertiary amino groups is studied by the polarization method. The study was performed at room temperature using 10- to 25-nm-thick layers in the SO2 concentration range of 100–3000 mg/m3. It is shown that the amount of the adsorbed sulfur dioxide is proportional to its concentration in the gas phase.

Semiconducting materials in the form of nanoclusters distributed in an organic or silicate matrix are of interest to researchers engaged in the field of nanoelectronics and nonlinear optics. These materials involve cadmium, zinc, lead, and mercury chalcogenides in silicate glass or Langmuir-Blodgett (LB) films of fatty acids [1-3]. Investigations in the field of chemical modification of multimolecular LB layers are of great importance for the design of organized molecular assemblies as new nonclassical objects in the physics of low-dimensional systems as well as functional molecular electronics and sensor technology [4]. Formation of lead, zinc, and cadmium sulfides as nanosized clusters by reactions of the corresponding metal behenate films with gaseous hydrogen sulfide was established in [5], where sulfidizing of behenate films was studied at different temperatures and pressures of hydrogen sulfide. In this work we study the structure of the sulfides. Formation of nanoclusters was established, and their size and concentration in the film were determined. Experimental procedure. Cadmium and lead behenate fdms were prepared by the Langmuir-Blodgett procedure. To create monolayers on the surface of a liquid we used hexane solutions of behenic acid and cadmium chloride and lead acetate solutions as a subphase with a concentration of 3-5-10 -4 M, pH 7.0. The monolayers were transferred at a surface pressure of 30-35 mN/m and temperature 22-23~ Conditions of film sulfidizing: H2S pressure 50-100 Torr, temperature 20-5C the holes were subsequently covered with a LB film. These were just the regions investigated by HREM. To obtain an electron diffraction pattern in the reflection mode, the films were applied to polished silicon single crystal plates. Cadmium and lead behenate films of 20 to 30 monolayers (corresponding to a film thickness from 60 to 90 nm) were studied prior to and after sulfidizing. Completeness of sulfidizing was monitored by IR spectra. Experimental results. According to electron diffractometry, cadmium behenate films are characterized by a distinct plate-like texture (Fig. 1). The lattice is hexagonal and has a c axis that is close, on the average, to the normal to the support. Scanning the film showed a 10 ~ change in the inclination of the c axis. The parameters of the hexagonal lattice of the crystal as determined from electron diffractograms are a = 4.8 ~ and c = n 7.5 ~, where n is an integer. Recording by the skewed texture method revealed periodic intervals of 2.2-2.5 A along the c axis, which may be due to periodicity of the arrangement of carbon atoms in aliphatic chains. The crystal structure of lead behenate is analogous