Stark spectroscopy of Langmuir-Blodgett monolayers and multilayers

The electrical (capacity and conductivity) and electro-optical (Stark spectra) properties were investigated for monolayers of an anthraquinone dye. The polar structure of the monolayers results in the appearance of the linear Stark effect with a field-induced change δT in the optical transmission proportional to the difference δμ of the dipole moments for an excited and the ground molecular states. Multilayers were shown to be non-polar owing to the effects of molecular association. In the latter case only the quadratic Stark effect is observed with δT proportional to the difference δ of the polarizabilities of an associated excited state and the ground state. It was also shown that the electric field distribution across an ultrathin Langmuir-Blodgett film is extremely non-uniform.     

Thermal behaviour of polymeric Langmuir-Blodgett multilayers

Langmuir-Blodgett multilayers of hydrocarbon and fluorocarbon polymers with hydrophilic spacer, lipid-polyelectrolyte complexes and mesogenic polymers have been prepared. The thermal behaviour of the multilayers was studied by small angle X-ray scattering, IR and UV—visible spectroscopy. Good thermal stabilities were found for the various classes of polymers. In addition, for both complexed multilayers and mesogenic polymer films, reorientation processes were observed.     

Composition and transfer mechanism of Langmuir-Blodgett multilayers of stearates

We determined the composition of Langmuir-Blodgett multilayers of several stearates from various experimental data and related these results to the type (Y or XY) of the layers. It is shown that the transfer of the XY layers can be accounted for without invoking an overturning mechanism.     

Formation of stable Langmuir-Blodgett multilayers from oxiran carboxylic acids

Long-chain carboxylic acids, having oxiran groups at various positions along the chain, were synthesized and tested for their capacity to form ordered monolayers and multilayers. The oxiran groups were included because of their potential for polymerization during electron beam lithography. The hydrophilic nature of both the carboxylic acid and the oxiran groups in the same molecule afforded some difficulties in film formation, but one of these compounds provided stable monolayers and multilayers. Initial investigations have revealed that these multilayers are sensitive to electron beam polymerization.     

An investigation of conductivity in metal-substituted phthalocyanine Langmuir-Blodgett films

Conductivity data for Langmuir-Blodgett films of cobalt, nickel, copper and zinc tetracumylphenoxy phthalocyanine complexes are presented as well as the changes in conductivity of the films induced by exposure to ammonia. An explanation is given for these results, supported by discrete variational X-α calculations of simple cobalt, nickel, copper and zinc phthalocyanine complexes and on calculations of these metals complexed with tetraazaporphyrin and ammonia. It was found that to some extent the conductivity can be correlated with the energy gap between the highest occupied and lowest unoccupied orbitals.     

Structural studies of Langmuir-Blodgett multilayers by means of soft X-ray diffraction

The specularly reflected intensity from cadmium arachidate multilayers has been measured as a function of incidence angle. The films were prepared by the Langmuir-Blodgett technique and ranged from three to 21 layers in thickness. Monochromatic synchrotron radiation of 1560 eV photon energy (wavelength 7.95 Å) was used in combination with a high vacuum compatible triple-axis diffractometer. The measured diffraction profiles were fitted with a theory based on the exact solution of the Fresnel-Bragg equations for multiple reflections including absorption. The optical parameters for the layers were taken from tabulated values, and the layers were constructed using a formulation similar to that employed previously by Pomerantz and Segmüller. The individual layer spacing as well as the total thickness of the film could be derived to within an accuracy of 1% or 1 Å (whichever is larger).     

Linear electro-optic properties of Langmuir-Blodgett multilayers of an organic azo dye

The surface non-linear susceptibility χ⁽²⁾_s (-ω;0,ω) of centrosymmetric (Y) and non-centrosymmetric (Z) odd numbers N of Langmuir-Blodgett multilayers of an azobenzene derivative (DPNA), are determined using the attenuated total reflection technique. It has been found that, for the two types of configuration and for a small number of monolayers (N11), χ⁽²⁾_s does not increase.     

Charge incorporation in ω-tricosenoic acid Langmuir-Blodgett multilayers

In order to investigate the amount of charge introduced into Langmuir- Blodgett (LB) films, multilayers of ω-tricosenoic acid have been deposited onto a number of silicon substrates under different dipping conditions. The effects of moisture and storage conditions on film properties have been examined, and a new mathematical model for the charge distribution within an LB film multilayer will be proposed.     

Effects of surface track potential on secondary electron emission and surface stopping power

In ion-surface scattering a positive surface track potential is induced on the surface behind the projectile due to ionizing collisions. The surface track potential is expected to affect secondary electron emission as well as the energy loss process of the projectile ions. We measure secondary electron yield induced by 0.5 MeV/u H⁺, He²⁺, Li²⁺ and B³⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The position-dependent secondary electron production rate was derived from the observed secondary electron yield. The secondary electron production rate is normalized by the mean square charge of the reflected ions. The normalized rate decreases with Z₁ suggesting that the surface track potential recapture the secondary electrons. We also measure the energy losses of 0.5 MeV/u H⁺, He²⁺, Li²⁺, B³⁺ and C⁴⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The observed result suggests that the surface stopping power is reduced by the surface track potential.     

Structure and thickness dependence of "molecular wiring" in nanostructured enzyme multilayers

Supramolecular organized multilayers composed of glucose oxidase (GOx) and osmium-derivatized poly(allylamine) redox polymer have been self-assembled electrostatically from Os-polyelectrolyte solutions of variable pH (5.5-8.8) leading to a decrease of the linear charge density in the PAH-Os with increasing pH. The layer-by-layer enzyme multilayers were studied by ellipsometry, quartz crystal microbalance, AFM, cyclic voltammetry, and electrocatalytic oxidation of beta-D-glucose. At higher adsorption solution pH, an increase in the film thickness, enzyme loading, and redox charge was observed. While the electrocatalytic response increases with the increase of the adsorption solution pH (decrease of the polyelectrolyte linear charge), the FADH2 oxidation bimolecular rate constant has a maximum in the pH range 7.0-7.5 where a change in the film growth mechanism is observed.     

BN表面改性对BN/环氧树脂复合材料导热性能的影响

采用十八烷基三甲基溴化铵（OTAB）阳离子表面活性剂对BN微米片进行有机化改性,研究了BN表面改性对BN/环氧树脂复合材料导热性能的影响。当OTAB浓度为0.6 g · L^-1时,BN表面的OTAB吸附量接近饱和。BN表面改性提高了环氧树脂对BN的浸润性,降低了BN的导热系数。SEM观察及黏度测试结果表明：BN表面改性改善了BN/环氧树脂复合材料的界面性能及体系相容性。由于界面热阻的降低,改性BN/环氧树脂复合材料的导热系数高于未改性BN/环氧树脂复合材料,当BN填充量为30%（填料与树脂基体的质量比）时,改性BN/环氧树脂复合材料的导热系数为1.03 W （m · K）^-1,是未改性BN/环氧树脂导热系数（0.48 W （m · K）^-1）的2.15倍。     

Effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers

FePt (50 nm) and [FePt(xnm)/AlN(1, 2, 3 nm)]₁₀ (x=2, 3 nm) films were prepared by RF magnetron sputtering technique, then were annealed at 550 °C for 30 min. This work investigates the effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers. Superlattice (0 0 1) peaks can be found in the grazing incidence X-ray diffraction of FePt and [FePt (3 nm)/AlN (1, 2, 3 nm)]₁₀ films, which indicate that the FCC phase has been partially transformed into ordered L1₀ phase. Compared with the single layer FePt film, superlattice (0 0 1) peaks of FePt/AlN multilayers are weak and wide, which indicates that the introducing of AlN hinders the growth of FePt particle, and also shows the introducing of AlN is not beneficial to the transformation from FCC phase to L1₀ phase. In addition, the low-angle XRD spectra show the layered structure of FePt/AlN has been broken after annealing. The coercivities, particle size, intergrain exchange interactions of FePt/AlN films are decreased with increasing AlN layer thickness.     

Electrical manifestation of dielectric non-centrosymmetry using Langmuir-Blodgett multilayers of ω-tricosenoic acid

Centrosymmetric (Y-type) and non-centrosymmetric (Z-type) Langmuir-Blodgett (LB) multilayers of ω-tricosenoic acid have been deposited as part of an M¦LB¦M structure and the electrical characteristics measured. The symmetry of the LB film was manifested in the electrical properties of the junction, with the behaviour of centrosymmetric LB films being independent of the applied bias sense and non-centrosymmetric LB films possessing a distinct bias sense dependence.     

The influence of surface diffusion on surface roughness and component distribution profiles during deposition of multilayers

The kinetic processes taking place on the surface and influencing the depth distribution of components during deposition of multilayers are considered by proposed kinetic model. The depth distribution of components in growing structure, broadening of interfaces between layers and shape of concentration peaks of multilayers are analyzed with respect of evolution of surface roughness during deposition. Surface roughness depends on adsorption rate and on surface diffusion. In presented model, the process of surface diffusion is subdivided into up-diffusion and down-diffusion. It is shown that atomic fluxes of up-diffusion and down-diffusion do not compensate each other even in the case of equal diffusion coefficients as they depend on coverage of different monolayers. Down-diffusion results in smoother surface, in contrary, up-diffusion makes it rougher. It is quantitatively shown by kinetic modeling that with increase of down-diffusion the amplitude of concentration peaks of components increases, the broadening of interface between layers decreases and concentration peaks become asymmetrical. The asymmetry of concentration peaks is found even in the case of equal diffusion coefficients of different components. At different diffusivity of components, the asymmetry is following: the concentration peaks of heavy-component (less diffusivity) show enhanced trailing tails on the back profile side (for light-component on the contrary). Up-diffusion results in increase of surface roughness and broadening of interface between layers. The quantitative functions of surface roughness on ratio of up- and down- diffusion coefficients are calculated and analyzed.