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Simple carbohydrates are associated with the enhanced risk of cardiovascular disease and adverse changes in lipoproteins in the organism. Conversely, sugars are known to exert a stabilizing effect on biological membranes, and this effect is widely exploited in medicine and industry for cryopreservation of tissues and materials. In view of elucidating molecular mechanisms involved in the interaction of mono- and disaccharides with biomimetic lipid systems, we study the alteration of dielectric properties, the degree of hydration, and the rotational order parameter and dipole potential of lipid bilayers in the presence of sugars. Frequency-dependent deformation of cell-size unilamellar lipid vesicles in alternating electric fields and fast Fourier transform electrochemical impedance spectroscopy are applied to measure the specific capacitance of phosphatidylcholine lipid bilayers in sucrose, glucose and fructose aqueous solutions. Alteration of membrane specific capacitance is reported in sucrose solutions, while preservation of membrane dielectric properties is established in the presence of glucose and fructose. We address the effect of sugars on the hydration and the rotational order parameter for 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) and 1-stearoyl-2-oleoyl-sn-glycero-3- phosphocholine (SOPC). An increased degree of lipid packing is reported in sucrose solutions. The obtained results provide evidence that some small carbohydrates are able to change membrane dielectric properties, structure, and order related to membrane homeostasis. The reported data are also relevant to future developments based on the response of lipid bilayers to external physical stimuli such as electric fields and temperature changes.

New analogues of the endogenous heptapeptide VV-hemorphin-5 (valorphin) synthesised by amino acid replacement allow for tailoring the peptide activity in vivo. Investigation of hemorphin-induced alterations of lipid bilayers' physicochemical parameters unravels membrane-mediated mechanisms of interaction with cells and subcellular structures. We studied the effect of modified valorphins with nociceptive activity on the structure, mechanical and electrical properties of lipid membrane models. Lower bending rigidity and higher specific capacitance of phosphatidylcholine bilayers were found in the presence of VV-hemorphin-5 analogues. Peptide partition constants for the transfer from the aqueous solution into the membrane were determined by isothermal titration calorimetry. It was found that the inclusion of non-proteinogenic acids with different number of methylene groups lead to alterations of hemorphin-membrane binding. The highest membrane affinity was obtained for a hemorphin derivative with dose-dependent variable effects on visceral nociception in mice. The valorphin analogue with the most pronounced anti-nociceptive effect in vivo induced the highest dipole and zeta potential change without significantly affecting the lipid packing at glycerol level in phosphatidylcholine bilayers.

Homogeneous films from SiOx (x = 1.2, 1.3) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide in vacuum. A part of the films was further annealed at 1000 °C to grow Si nanocrystals in a silicon dioxide matrix. Homogeneous and composite films with initial x = 1.2 were irradiated by 20-MeV electrons at a fluence of 3.6 × 1015 electrons/cm2 and the effect was compared with that caused by irradiation of films with x = 1.3 at much lower fluence of 2.4 × 1014 electrons/cm2. Transmission electron microscopy, infrared transmission and Raman spectroscopies and spectroscopic ellipsometry were used to get information about the SiOx films composition, nanoparticle crystallinity and space distribution as well as for electron-beam induced changes in the nanocrystal size. The infrared data have indicated that electron irradiation with 3.6 × 1015 electrons/cm2 induced phase separation in the homogeneous films with x = 1.2. Not only silicon nanocrystals but also a small amount of amorphous silicon phase have been detected in the composite films before and after electron irradiation. Nanocrystallite size decrease induced by the electron beam irradiation at a fluence of 3.6 × 1015 electrons/cm2 has been assumed on the basis of the observed changes in the effective refractive index, extinction coefficient and nanocrystallite volume fraction in the composite films.

Understanding sugar-membrane interactions is of fundamental and technological relevance considering the role of sugars in drought-protection mechanisms of plants as well as the cryo- and bio-preserving effect of carbohydrates in many industrial and medical applications. In this work, we investigated the effect of sucrose on the electrical properties of membranes. In particular, we measured the specific capacitance of palmitoyl-oleoyl phosphatidylcholine membranes in aqueous solutions of sodium chloride. Different concentrations of sucrose were examined. The capacitance was assessed from the frequency-dependent deformation of giant unilamellar lipid vesicles in alternating electric field. Our measurements on giant vesicles in sugar-free aqueous solutions yield lower specific capacitance compared to values obtained for suspended and supported bilayers. This might be a result of the higher membrane tension in the latter systems, which is coupled to smaller thickness of the bilayer. We also report an increase of the bilayer capacitance upon increasing the sugar content in water. This finding is consistent with the sugar-induced thinning of membranes reported in the literature. However, the thinning is not sufficient to explain the observed capacitance increase with rising sugar concentration. We interpret the trend as resulting from an increase in the membrane dielectric permittivity.

Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 °C by pulsed laser deposition. A polycrystalline AlN target was multipulsed irradiated in a nitrogen ambient, at different laser pulse repetition rate. Grazing Incidence X-Ray Diffraction and Atomic Force Microscopy analyses evidenced nanocrystallites with a hexagonal lattice in the amorphous AlN matrix. The thickness and optical constants of the layers were determined by infrared spectroscopic ellipsometry. The optical properties were studied by Fourier Transform Infrared reflectance spectroscopy in polarised oblique incidence radiation. Berreman effect was observed around the longitudinal phonon modes of the crystalline AlN component. Angular dependence of the A1LO mode frequency was analysed and connected to the orientation of the particles’ optical axis to the substrate surface normal. The role of the laser pulse frequency on the layers’ properties is discussed on this basis.

Aluminum nitride (AlN) films were synthesized onto Si(100) substrates by pulsed laser deposition (PLD) in vacuum or nitrogen, at 0.1, 1, 5, or 10 Pa, and substrate temperatures ranging from RT to 800 &deg, C. The laser parameters were set at: incident laser fluence of 3&ndash, 10 J/cm2 and laser pulse repetition frequency of 3, 10, or 40 Hz, respectively. The films&rsquo, hardness was investigated by depth-sensing nanoindentation. The optical properties were studied by FTIR spectroscopy and UV-near IR ellipsometry. Hardness values within the range of 22&ndash, 30 GPa and Young&rsquo, s modulus values of 230&ndash, 280 GPa have been inferred. These values were determined by the AlN film structure that consisted of nanocrystallite grains, strongly dependent on the deposition parameters. The values of optical constants, superior to amorphous AlN, support the presence of crystallites in the amorphous film matrix. They were visualized by TEM and evidenced by FTIR spectroscopy. The characteristic Reststrahlen band of the h-AlN lattice with component lines arising from IR active phonon vibrational modes in AlN nanocrystallites was well detectable within the spectral range of 950&ndash, 500 cm&minus, 1. Control X-ray diffraction and atomic force microscopy data were introduced and discussed. All measurements delivered congruent results and have clearly shown a correlation between the films&rsquo, structure and the mechanical and optical properties dependent on the experimental conditions.

We present the investigations on the nature of the white paste used for incrustations on pottery from Early and Late Chalcolithic period (IV mill BC) found in two regions on the territory of Bulgaria. Fourier Transformed Infrared (FTIR) spectroscopy, Laser-Induced Breakdown Spectroscopy (LIBS) and X-ray powder diffraction (XRD) were carried out for determination of the material constituents and structure. The resulting spectra revealed different consistency of the incrusted white substance: bioapatite, gypsum and calcites based on inorganic mixtures, thus proving the knowledge of various techniques in the ancient manufacturing process and the possible ties with the prehistorical Balkans cultures in the near by areas around.

A novel analog of VV-hemorphin-5 containing azobenzene moiety has been synthesized and investigated for anticonvulsant activity in relation to its E → Z photophysical properties activated by long wavelength light at 365 nm. The synthesis was achieved by a modified SPPS by Fmoc-dimerization strategy. The electrochemical behavior before and after UV illumination was investigated using different voltammetric modes. The number of electrons transferred, heterogenic rate constant and diffusion coefficient for E- and Z-isomers were also evaluated. Revealing the governing principles involved in signaling and nerve pulse propagation requires the detailed characterization of the electrical properties of cell membranes. For probing the effect of synthesized azo-peptide on the membrane electrical properties, we measured the specific capacitance of lipid bilayers, representing a basic physical model of biomembranes with their simple reproducibility in laboratory conditions at controlled membrane composition and physicochemical parameters of the surrounding aqueous medium. Our results have shown reduced membrane capacitance in the presence of the azo-peptide, thus providing evidences for possible alterations in the dielectric permittivity of the bilayer. The (Val-Val-Tyr-Pro-Trp-Thr-Gln)2Azo peptide was explored also in vivo for preliminary anticonvulsant activity by using the 6-Hz seizure test and pentylenetetrazol (PTZ) seizure test in mice. The Z-isomer has exhibited higher potency compared to E-isomer most pronouncedly in the 6 Hz test for psychomotor seizures where the compound had activity at all three tested doses. It was found that the Z-isomer decrease the latency for onset of clonic seizures induced by PTZ. These results demonstrate that the Z-isomer deserves further evaluation in other screening tests for anticonvulsant activity.

Advances in condensed matter physics 2018, 7158079 (2018). doi:10.1155/2018/7158079, Glasses with composition of Ge$_x$Sb$_{40-x}$Se$_{60}$ (x= 40, 35,32, 27, 20, 15 at. %) have beensynthesized. Neutronand X-ray diffraction techniques were used to study the atomic glassy structure,and Reverse Monte Carlo(RMC) simulations were applied to model the 3-dimensional atomic configurations and thorough mapping of the atomic parameters, such as first and second neighbour distances, coordination numbers, and bond-angle distributions. The results are explained with formation of GeSe$_4$ and SbSe$_3$ structural units, which correlate with the Ge/Sb ratio. For all the studied compositions, the Ge-Se, Sb-Se, Ge-Ge, and Se-Se bonds are significant. RMC simulations reveal the presence of Ge-Sb and Sb-Sb bonds, being dependent on Ge/Sb ratio. All atomic compositions satisfy formal valence requirements, i.e., Ge is fourfold coordinated, Sb is threefold coordinated, and Se is twofold coordinated. By increasing the Sb content, both the Se-Ge-Se bonds angle of 107±3° and Se-Sb-Se bonds angle of 118±3° decrease, respectively, indicating distortion of the structural units. Far infrared Fourier Transform spectroscopic measurements conducted in the range of 50-450 vm$^{-1}$ at oblique (75°) incidence radiation have revealed clear dependences of the IR band’s shift and intensity on the glassy composition, showing features around x=27 at.% supporting the topological phase transition to a stable rigid network consisting mainly of SbSe$_3$ pyramidal and GeSe$_4$ tetrahedral clusters. These results are in agreement with the Reverse Monte Carlo models, which define the Ge and Sb environment., Published by Hindawi Publ. Corp., New York, NY ˜[u.a.]œ

Aluminium nitride (AlN) films were synthesized by pulsed laser ablation of poly-AlN target on Si(100) substrates using a KrF* excimer laser source (λ = 248 nm, τFWHM ≤ 25 ns), with incidence laser fluence of ~ 3 J/cm2 and laser pulse repetition frequencies (LPF) of 3, 10 and 40 Hz, respectively. The depositions were performed in nitrogen pressure of 0.1 Pa and at substrate temperatures of 450 and 800 °C. The AlN structures were studied by transmission electron microscopy, atomic force microscopy (AFM), Fourier transform infrared reflectance (FTIR) spectroscopy and spectroscopic ellipsometry (SE) measurements. The results show that at 450 °C and LPF of 3 Hz the AlN film is entirely amorphous, while at LPF of 10 and 40 Hz nanocrystallites with h-AlN phase appear in the grown films. At 800 °C, well-textured h-AlN nanocrystallites with columnar grains are formed. Growth of nanocrystallites in the 450 °C AlN films, similar to films grown at 800 °C, is possible when the films are deposited onto a high-temperature AlN “seed” layer, as they follow the columnar structure but with small-sized crystallites and a weaker texturing. AFM imaging reveals increasing surface roughness with the degree of crystallinity in the synthesized films. The structural changes are well correlated with the variation in the optical parameters registered by FTIR and SE.

The occurrence of new textures of liquid crystals is an important factor in tuning their optical and photonics properties. Here, we show, both experimentally and by numerical computation, that under an electric field chitin tactoids (i.e. nematic droplets) can stretch to aspect ratios of more than 15, leading to a transition from a spindle-like to a cigar-like shape. We argue that the large extensions occur because the elastic contribution to the free energy is dominated by the anchoring. We demonstrate that the elongation involves hydrodynamic flow and is reversible, the tactoids return to their original shapes upon removing the field., Comment: 8 pages, 6 figures; accepted for publication in Physical Review E

Homogeneous films from SiO1.3 (250 nm thick) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide. A part of the films was further annealed at 700 °C to grow amorphous Si (a-Si) nanoclusters in an oxide matrix, thus producing composite a-Si-SiO1.8 films. Homogeneous as well as composite films were irradiated by 20-MeV electrons at fluences of 7.2 × 1014 and 1.44 × 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the phase composition of the films caused by the electron-beam irradiation was studied by transmission electron microscopy. The ellipsometric and electron microscopy results have shown that the SiOx films are optically homogeneous and the electron irradiation with a fluence of 7.2 × 1014 el/cm2 has led to small changes in the optical constants and the formation of very small a-Si nanoclusters. The irradiation of the a-Si-SiOx composite films caused a decrease in the effective refractive index a...

Mono- and di-(trimethylammonium)-terminated polystyrenes with similar molar masses were synthesized. Bromopolystyrenes were first prepared by atom transfer radical polymerization (ATRP) using (N-Boc-propylamino)-2-bromoisobutyrate as initiator and Cu(I)Br/2,2'-bipyridine as catalytic system in bulk at 110 °C. α,ω-Telechelic polymer with double molecular weight with respect to the starting polystyrene was then obtained under atom transfer radical coupling process using 2,2/-bipyridine and copper(0) mediated reductive conditions in anisole. Final (trimethylammonium)-terminated polystyrenes were eventually obtained after removal of the tert-butyloxycarbonyl group and permethylation reactions. Intermediate and final polymers were characterized by 1 H NMR. The aligning properties of the obtained polymers for liquid crystals have been investigated. Pretilt and zenithal anchorings on ITO/glass substrates were measured. Finally, the possibility for the telechelic polystyrene to form a network in an inverted microemulsion was also considered.

The Czochralski and floating zone methods are used to grow single crystals of gallium perovskites solid solutions with rare earth elements La, Pr and Nd for structural, Raman and IR spectroscopy investigations. The contraction of the unit cell results from decreasing of the averaged radius of rare earth ions and causes increasing tilting and deformation of GaO6 octahedra. The volume of the GaO6 octahedra increases despite the decrease of the unit cell volume. Thus, the ratio of the perovskite unit cell to the octahedron volume decreases with the decrease of the unit cell volume and is determined to be 5.72 in LaGaO3 and 5.5 in NdGaO3. The temperature dependence of the Raman spectra demonstrates a first order phase transition at about 150 °C. The shift of the Raman modes slightly decreases with x increasing independently of the rare earth ion type. Evolution of the IR spectra with x is also discussed.

We study the zenithal anchoring strength of the nematic 5CB on holographic gratings of different amplitudes and a period Λ=0.5 μm. The surface monostable planar anchoring can be broken by short external electric pulses after which the director displays bistable textures: uniform and half-turn twisted. The measured threshold of the surface anchoring breaking is about 6 V/μm and is independent from the grating amplitude.

The azimuthal anchoring strength and easy axis gliding of the nematic 5CB on holographic gratings were measured. Relation between the aligning elastic forces and the inelastic gliding of the surface easy axis for different grating amplitudes was established. Azimuthal extrapolation lengths of the gratings were estimated.

A new class of mixtures: 4, n -alkyloxybenzoic acids ( n -OBA) and 4-hydroxypyridine (HOPY) are investigated using FT-Far IR spectroscopy and polarisation microscopy. The macroscopic (chirality and structure phase transition induced by the mixture) and the spectroscopic (dynamic of the OH-bond deformation vibrations) characteristics of the complexes built through the bonding of both kinds of molecules are discussed. A weight ratio n -OBA:HOPY about 20 is predicted to be the most effective for realisation of a consistence with suitable chiral and anisotropic properties. The influence of the hydrophilic (polyvinylalcohol) and hydrophobic (polyimide) orienting surface on the spectral and textural properties of the complex is considered. A pronounced liquid crystal (characterized with fluid chains)–gel (rigid chains) transition was observed. An aggregation mechanism of the complex realization is suggested.

We describe the synthesis and characterization of aligned carbon nanotubes deposited on quartz substrates by pyrolysis of a xylene–ferrocene mixture at 700 °C at atmospheric pressure. For microscopic characterization of the pyrolyzed products, scanning and transmission electron microscopies and scanning tunneling microcopy were used, and properties of bulk samples were characterized by Raman spectroscopy and x-ray powder diffraction methods. The nanotubes have topological defects and many contain metal particles. Scanning tunneling spectroscopy proved that the nanotubes had a metallic electrical conductivity with resonant states near the Fermi energy. The states are ascribed to the dangling bonds originating from the defects.

A microscopical mechanism of the interaction between dimerized nematics of 4, n -alkyloxybenzoic acids and hydrophilic solid surfaces is developed. The liquid crystal molecules: monomers and closed dimers are considered like dipoles and quadrupoles, respectively. It is demonstrated that in the low-temperature and the high-temperature ranges of the nematic phase, the mechanisms of the microscopical interaction are different thus providing different macroscopical effects. The cell thickness and the temperature trends of the scalar order parameter, the effective surface energy and the concomitant anomalies in these trends are discussed on the basis of the proposed microscopical mechanism.

C 60 was reacted with cobaltocene and nickelocene. The samples of the composition C 60 (Cocp 2 ) 3 and C 60 Nicp 2 were obtained in the reaction. Their thermal stability was measured by Thermogravimetry and Differential Scanning Calorimetry and the vibrational spectrum was investigated by infrared absorption. Hydrocarbon groups may be evacuated from the reaction products by annealing, while metal atoms remain dispersed between fullerenes. The experiments are compared with the molecular modeling results obtained by applying the PM3 model.

The temperature and the cell thickness trends of the scalar order parameter for the dimerized nematic with short-range smectic order of 4, n -nonyloxybenzoic acid (NOBA) are indicated by FT-FIR spectroscopy. The temperature dependence of this parameter shows an anomaly, in respect to the dependence typical for the classical nematics, at a definite temperature T ∗ in the nematic range. The scalar order parameter increases nonlinearly at cell thickness ( d ) decreasing between 20 and 6 μm and goes to saturation when d →∞, while below 6 μm down to 2 μm it decreases tending to a finite small value. It is indicated that the order parameter increasing of 0.035 with the thickness decreasing from 20 to 6 μm is comparable to order increasing induced by a stabilizing electric or magnetic fields; the order parameter decreasing at small cell thickness is an analog of a disordering induced by destabilizing fields. The anomalies in the temperature and cell thickness trends of the scalar order parameter are explained by the dynamics of the hydrogen bonding of the monomers in dimers stimulated by temperature and surface action variations. The relation between the surface order parameter square and the anchoring energy is indicated to be a linear dependence near the nematic–isotopic phase transition temperature. The trend of the anchoring energy on the cell thickness is explained by a modification of the Rapini–Papoular surface energy as an effective one, adding one dielectric part stimulated by phenomena as: existence of a double electric layer, thickness dependence of the surface charge density and surface polarization.

Using far-IR spectroscopy, the temperature dependence of the conformational order parameter of the nematics with flexible molecules (sixth, ninth and tenth homologues of p-n-alkyloxybenzoic acids) is found to deviate from that known for the orientational order parameter of the classical nematics. Conformational order ↔ disorder at a critical temperature T ∗ is indicated. Short-range smectic order fluctuations are detected in the sixth homologue and which do not display smectic C phase in its bulk phase diagram.

Methylnaphthalenes form mixed crystals with C 60 . The molecules in these crystals are so densely packed, that the flat methylnaphthalene molecules undergo a deformation. The deformation is observed by the shift of the characteristic infrared and Raman active modes. However the modes of the rigid C 60 cage remain at the same positions, indicating that the C 60 molecules are not significantly deformed.

International audience; Clay minerals, like beidellite or nontronite, spontaneously exfoliate in water and form colloidal suspensions of nanosheets. In a given range of concentration, these suspensions display a nematic liquid–crystalline phase whose structure and properties can be conveniently studied in detail by polarized-light microscopy and small-angle X-ray scattering (SAXS). Moreover, in situ SAXS investigations of sheared clay suspensions provide information about their flow properties, both in the isotropic and nematic phases. The colloidal nematic phase shows the classical properties of usual nematics, such as surface anchoring and electric-field and magnetic-field alignment. Thus, nematic single domains can be produced. The isotropic phase also displays strong electro-optic effects in moderate electric fields. Finally, we describe a few examples of applications of such systems and we show how these studies could be extended to suspensions of other types of nanosheets.

The electronic structure of C60 molecules with carbon substituted by other elements such as boron or nitrogen has been calculated for molecules in the singlet state with even number of electrons. Therefore, in the case of boron and nitrogen substituents, calculations have been performed for ionized molecules. The results obtained from our density functional calculations prove than in the C60-x-yBxNy molecules both HOMO and LUMO levels are split due to the lower symmetry of the molecule Influence of deformation of C60 molecules on electronic states, which is interesting because fullerenes may undergo deformation in solvate crystals, is also shown These C59B and C59N, as well as C58BN molecules are of special interest because samples containing such species can be prepared The Electron Spin Resonance (ESR) in those samples differs from the results obtained in pure C60 samples, it consists of several lines which are very sensitive to the temperature.

We synthesized undoped as well as up to 6 at.% nitrogen (N) doped thin amorphous carbon (α-C) films by plasma- enhanced chemical vapor deposition (PECVD) method. The source of carbon/carbon containing radicals was benzene (C6H6) in Ar gas- mixture. The obtained thin films were studied by optical microscopy, X-ray powder diffraction, UV-VIS- NIR Spectral Ellipsometry, IR and Raman spectroscopic studies as well as by X-ray photoelectron spectroscopies (XPS). We established by XPS that the deposited layers consist of a mix of sp2 and sp3 hybridized carbon. The films are amorphous as it was shown by the measured XRD patterns. The ellipsometric measurements enabled calculation of transition energies and the complex results showed that films with thickness of 15- 120 nm and different properties can be obtained by this technique.

The 6 - 10th homologues of 4-n-alkoxybenzoic acid, i.e. hexyl-, heptyl-, octyl-, nonyl- and decyloxybenzoic acids (60BA, HOBA, OOBA, NOBA and DOBA) are used for the present investigations. Far IR spectroscopy is used to study the state of hydrogen bonding at temperature variation of the nematic liquid crystal phase. The observed spectral bands are assigned to different OH deformation vibrations. From the analysis of the temperature dependence of the spectral band widths a cyclic ↔ open dimer transformation is indicated at different vibration frequencies and polarizations. The activation energy for the dimer and monomer reorientation is calculated and compared with that per hydrogen bond. The correlation lengths parallel and perpendicular to the nematic director (ξ‖ and ξ⊥) are calculated and an anisotropy is found in the temperature dependence of the critical index of the correlation length. A comparison with nonoriented nematics with hydrogen bonded molecules is presented.

Far-infrared transmittance spectra (200-30 cm−1) of the hydrogen bond in cyclic dimers of 4-n-heptyl-, octyl- and nonyloxybenzoic acids are observed and investigated. The spectral bands at 42, 63, 68 and 82 cm−1 are assigned to the four deformation vibrations: twisting, bending (in and out of the dimer ring plane) and stretching by halfwidth spectral band temperature analysis. The hydrogen band evolution in the isotropic and nematic phases is investigated. A cyclic ↔ open dimer transformation at different vibration frequencies and polarizations is shown. The critical character of the temperature T ∗ , defined as the temperature dividing the nematic phase of the nematics with hydrogen-bonded molecules into high-temperature (classical) and low-temperature (smectic-like) subphases, is demonstrated.

Aluminum Nitride (AlN) films were deposited at 450°C in nitrogen ambient at a pressure of 0.1 Pa and at a laser incident fluence of ~3 J/cm2 and pulse repetition rate of 40 Hz. Grazing Incidence X-ray Diffraction patterns evidenced the presence of nanocrystallites in the amorphous AlN matrix. In the FTIR spectra the characteristic Reststrahlen band of AlN crystal with a hexagonal lattice is observed but it is quite broadened (950-550 cm-1). The angular dependence of the reflectance spectra in p-polarised incidence radiation demonstrates the sensitivity of the A1LO phonon mode of the AlN nanocrystallites to their orientation toward the normal to the substrate surface. With decrease of the incidence beam angle the intensity of the A1LO phonon mode diminishes and softening of the resonance frequency occurs.

The equilibrium constant for the equilibrium 2(monomer) ↔ dimer is calculated and as a result the energy per linear hydrogen bond is estimated. The hydrogen bond force constants (in the harmonic approximation) dependence on the deformation vibration frequencies is found. The activation energy for the dimer and monomer reorientation is calculated and compared with that per hydrogen bond. The critical character of the temperature T * (defined as the temperature dividing the nematics with hydrogen-bonded molecules into high-temperature (classical) and low-temperature (smectic-like) subphases) is demonstrated. The anisotropy of the critical index of the correlation length temperature dependence is found. The correlation lengths parallel and perpendicular to the nematic director (ξ | and ξ ⊥ ) are calculated. A theoretical conclusion concerning T * shifting at a set of bulk elastic deformations is confirmed. A value (1.036) for the critical index μ ⊥ of NOBA is found. This value coincides with that characterizing the susceptibility temperature dependence of He 4 and is interesting since the corresponding critical index cannot be measured in the superfluid.

Far-IR spectroscopy (200−30 cm−1 was used to study the temperature evolution of the hydrogen bonds in the nematic liquid crystal phase of 4, n-heptyl-, octyl- and nonyl-oxybenzoic acids (HOBA, OOBA and NOBA). The observed absorption bands (νOH = 82, 68, 63 and 42 cm−1) are assigned to the four predominant vibrations respectively — stretching, bending (out of and in the dimer ring plane) and twisting. From a spectral band half-width temperature analysis hydrogen-bond evolution in the isotropic and nematic phases is investigated. A cyclic ⇌ open dimer transformation at different vibrational frequencies and polarizations is indicated.

We study the electric-field-induced birefringence and orientational order in the isotropic phase of aqueous suspensions of exfoliated natural beidellite clay particles, thin (L = 0.65 nm) flat charged sheets with high aspect ratio, D/L ≈ 300. Our electric birefringence experiment is optimized for aqueous suspensions of colloidal particles, with a high frequency a.c. electric field, ν ≈ 1 MHz, applied by two external electrodes to a thin flat sample, sealed in an optical capillary. In isotropic and biphasic samples, we observed strong field-induced birefringence Δn(E), saturating at moderate E(sat) field to a plateau Δn(sat) proportional to the volume fraction ϕ. The field-induced order parameter S(E) is negative and saturates to S(sat) = -0.5 above E(sat). This corresponds to a perfect "anti-nematic" order, i.e. the normals of the beidellite particles are perpendicular to the field, without any preferred azimuthal direction. The measured specific excess polarizability ΔA(sp) is among the highest data reported for other strongly anisometric dielectric and metal particles. We explain the high ΔA(sp) value with the strong induced polarization of the electric double layer of counterions at the charged particle/electrolyte interface. The estimated equivalent conductivity of the beidellite particle K(eq) = 2 K(σ)/L is several orders of magnitude larger than the bulk conductivity of the electrolyte K(e), resulting in a metal-like behavior of the beidellite disks under field. In the isotropic regions of biphasic nematic/isotropic samples, the excess polarizability is further enhanced by an order of magnitude, indicating collective reorientation of the particles. We propose that this enhancement might be due to pretransitional fluctuations of the spontaneous nematic order S(N) of the colloidal suspension and/or formation of chains of particles, with antinematic order of the beidellite disks in the chains.

International audience; We present in this Rapid Communication experimental evidence of an acceleration of the zenithal easy-axis dynamics of a nematic liquid crystal (NLC) with the age of a NLC-polymer layer. The comparison with other hard alignment layers strongly indicates that the polymer softness and its ability to reorient in the nematic ordering field is at the origin of the measured dynamics. The unusual acceleration of the dynamics with the polymer age is discussed in terms of this unique coupling with the NLC order. The NLC behaves like a physical plasticizer as a result of the coupling between the NLC and the polymer orders.

A highly ordered structure for a poly[methyl-3-(9-carbazolyl)propyl]siloxane film was obtained on a glass substrate. Reflectance and transmittance spectra in the spectral region 30000-400 1 were measured and the dispersion of the refractive index n and the extinction coefficient k in the visible and near-infrared regions were obtained from these measurements. Surface electromagnetic wave (SEW) measurements were carried out. The propagation length L of the SEW was measured both parallel and perpendicular to the main brain axis and some anisotropy was observed. The absolute values of L were determined to be about several hundred micrometers.

The optical properties and the structure of thin titanium nitride substoichiometric and stoichiometric films were studied as a function of the conditions of film deposition. Optical constants of the non-transparent layers (thickness 2500 A) were determined by both dispersion analysis of the reflectance spectra and surface electromagnetic wave (SEW) phase spectroscopy methods. A new application of the selective reflection properties of the films in radiometry is suggested.

We present experimental evidence of zenithal gliding of the nematic easy axis on a polyimide surface. The reorientation dynamics of the easy axis under external torque, and its relaxation, are extremely slow processes which cannot be described by a single exponential time. They show similarities with aging phenomena previously encountered in glassy systems. At last, the adsorption-desorption-readsorption process which empirically justifies the azimuthal easy axis gliding may also explain our observations.

A study of the structural development of hydrogenated amorphous silicon (a-Si : H) during plasma-enhanced chemical vapour deposition with hydrogen-diluted silane has been carried out with focus on the variations in the hydrogen bonding configuration and in the amorphous silicon network with increasing film thickness. In addition, the hypothesis of a high fraction of non-bonded (molecular) hydrogen in a-Si : H has been tested. The total hydrogen concentration and its silicon-bonded fraction have been estimated by means of nuclear reaction analysis and infrared spectroscopy, respectively. It has been shown that the presumable molecular hydrogen is not detectable within the limits of the measurement accuracy of the methods used. The hydrogen concentration is uniformly distributed along the growth direction, and the infrared absorption modes at 2000 and 2100 cm−1 are not affected by increasing the film thickness. Raman spectroscopy has been used to follow the variations in the structure of the silicon network. The increase in the film thickness leads to an improved ordering of the amorphous network on the short and medium range scale for films deposited at low substrate temperatures. In films deposited at high substrate temperatures, the tendency of structural improvement has been detected only on the medium range scale.

Optical properties and optical constants of thin solid films of TiN x and SnO x were investigated by means of both Fourier transform IR spectrometry and very sensitive surface electromagnetic wave phase spectrometry. Layers of TiN x have low reflectance over the UV and visible spectral regions and high reflectance in the thermal IR region. Films of partially oxidized tin, SnO x , lead to a relatively narrow low reflectance peak in the “reststrahlen” band of the crystalline quartz, which overlaps some of the CO 2 laser lines. Hence both kinds of films can be used to increase the sensitivity of radiometers made on the basis of quartz resonators.

The standard electric arc generator was used to prepare fullerenes substitutionally doped on the surface with boron and nitrogen. The material is a unique case of a molecular crystal of high symmetry, consisting of molecules of extremely low C s symmetry. FT-IR and FT-Raman spectra of the C58BN were measured in the spectral region 2000™30 cm™1 and over a large temperature interval: 14−300 K.

The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness.

Nematic and isotropic aqueous suspensions of beidellite clay sheets have been submitted to magnetic and a. c. electric fields. The nematic suspensions have positive anisotropy of magnetic susceptibility and negative anisotropy of electric susceptibility because the clay sheets orient their normals parallel to the magnetic field but perpendicular to the electric field. Moreover, the isotropic phase shows a large electric-field-induced birefringence. By dissolving acrylamide monomers in the clay suspensions and photopolymerization, clay/polymer composite gels could be elaborated. Aligned and patterned composites could be produced by application of an electric field during polymerization.