Specific features of absorption spectra of fractal-structured silver sols

Effects exerted on plasmon absorption spectra by different characteristics of aggregating silver sols with a fractal distribution of particles whose sizes are in the range 5–30 nm are studied by mathematical simulation with the aid of a modification of the method of coupled dipoles. Distinctive features of plasmon absorption contours of silver sols having different particle-size distribution functions and different properties of the adsorption layers of the particles are explained.     

Saturable absorption and reverse saturable absorption on silver particles with different shapes

Micro/nanostructured silver particles with different shapes (flower, wire, and rod) have been prepared and characterized. All the open aperture z-scan curves of silver microrods and silver nanoflowers present a typical reverse saturable absorption. With the increase of incident intensity, the nonlinear absorption coefficients and the third-order optical susceptibilities ImX⁽³⁾ of nanoflowers increase, but those of silver microrods decrease. Moreover, the silver nanowires show the conversion from saturable absorption to reverse saturable absorption. There was no definite correlation between incident intensity and nonlinear absorption coefficient (β) under the conditions studied herein. And nonlinear optical properties of micro/nanostructured silver particles are dependent on the particle shape in suspensions at 800 nm.     

Influence of isovalent substitutions on absorption spectra of orthoferrities

The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on the optical absorption of orthoferrites that are promising for magnetooptics is studied. Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072, Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997.     

具有幂次相互作用的磁性粒子凝聚过程的数值研究

在扩散限制凝聚模型的基础上引入粒子的自旋自由度(包括自旋向上和向下),并假设粒子间存在幂次Ising磁相互作用,采用Monte Carlo方法研究了在不同相互作用力程情况下磁性粒子的分形生长规律.模拟结果表明,当粒子间以反铁磁方式耦合时,凝聚体中的粒子自旋交替凝聚.当粒子间以铁磁方式耦合时,凝聚体中粒子的自旋分布与相互作用力程有关:对于短程作用系统,凝聚体中存在大小不同的自旋畴块,即为铁磁生长;而对于长程相互作用系统,凝聚体中的自旋出现反常分布,即中心区域是近似反铁磁生长的结构,其外围后续生长的粒子却保持 关键词： 幂次相互作用 扩散限制凝聚模型 自旋     

Effect of phytochemicals on optical absorption spectra during biogenic synthesis of self-assembled silver nanoparticles and studies relevant to food applications

The facile biogenic synthesis of silver nanoparticles was done using avocado seed aqueous extract and silver salt. Avocado seed aqueous extract was used as an active biomolecule for in situ fabrication of self-assembled silver nanoparticles. This green approach to the mechanism for the formation of uniform sized silver nanoparticles was studied by ultraviolet-visible spectroscopy, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The effect of incubation time, concentration of silver nitrate, and avocado seed extract concentrations in the synthesis of silver nanoparticle was studied. Spectral splitting in the visible region with the generation of a new plasmon resonance band resulted with concurrent increase in the concentration of phytochemicals and reaction time during the synthesis of particles was observed. This was due to the chemisorption of phytochemicals accompanied by a charge-transfer transition, which may be responsible for the organization and self-assembly of nanoparticles. The phytochemicals present in the extract acted as a reducing agent and simultaneously fabricating the nanoparticles with the phenolics and sugar compounds. The antibrowning and antibacterial activity of silver nanoparticles were tested and could be exploited for their use in food packaging and preservation.     

Influence of interactions on the hopping conductivity of classical particles

We study interaction effects in ionic conductors within Kawasaki's kinetic Ising model. The hopping rates are related to properties of the interaction potential. Numerical results from a continued fraction expansion are presented for a one-dimensional chain. They show that the dynamic conductivity depends considerably on the choice of the rates.     

Influence of thermal fluctuations on the interactions between nanoscale particles

We present a method to investigate the influences of the thermal fluctuations on the nanometer-sized particle in pickup manipulation by an atomic force microscope (AFM). We show that thermal fluctuations can play an important and even major role in the interaction between particles at room temperature. Moreover, thermal fluctuations always have an opposing effect on the particle interactions. The deterministic directional motion of a particle governed by the interfacial properties of the nanoparticles becomes non-deterministic, with a reduction of the adhesion probability up to 44% under different strength of the thermal fluctuations.     

The aggregation effects on the two-photon absorption properties of para-nitroaniline polymers by hydrogen-bond interactions

This paper has theoretically designed a series of aggregate polymers on the basis of several para-nitroaniline monomers by hydrogen-bond interactions. At the level of time-dependent hybrid density functional theory, it has optimized their geometrical structures and studied their two-photon absorption (TPA) properties by using analytical response theory. The calculated results exhibit that the aggregation effects not only bring out the considerable red shift of the excited energies but also greatly enhance the TPA intensities of the aggregate polymers in comparison with the para-nitroaniline monomer. The aggregate configurations also have an important influence on the TPA abilities of the polymers; the trimer has the largest TPA cross section. The electron transitions between the molecular orbits involving the strong TPA excitations of the trimer are depicted to illuminate the relationship between the intermolecular charge transfer and the TPA property.     

Concentration and pH dependent SERS spectra of sulfanilic acid sodium salt on colloidal silver particles

IR, Raman and surface‐enhanced Raman scattering (SERS) spectra of sulfanilic acid sodium salt (SANA) were recorded and analysed. The vibrational wavenumbers were computed by the density functional theory method using the B3LYP/6–31G* basis and found to be in good agreement with the experimental values. The effect of concentration and pH dependence on the SERS intensity of the molecule was also studied. The molecular plane assumes a tilted orientation with respect to the silver surface. The observed changes of the relative intensities of some enhanced bands and the presence of in‐plane and out‐of‐plane modes of the phenyl ring suggest that the molecule assumes a more tilted orientation upon lowering the concentration of the adsorbate. Copyright © 2009 John Wiley & Sons, Ltd.     

Symmetries of the electrodynamic interactions between chiral molecules

A quantum electrodynamics calculation of the dynamic microscopic interactions between molecules beyond the electric dipole approximation is presented. The symmetry of the resulting terms is examined with respect to rotations, parity and index permutations. Their relative importance is also considered in the short-distance limit. A dominant term which exists only in chiral molecules and which involves the coupling of the anisotropic parts of the molecular optical activities is evidenced. Associated with the coupling of the anisotropic parts of the molecular polarisabilities which is usually invoked to account for the isotropic–nematic phase transition of liquid crystals, that term accounts for the possibility of the helical order which is observed in chiral nematics (cholesterics). Introducing in addition both the short-range correlations due to the exclusion principle driven repulsive forces and the thermally-induced effect of the static multipole interactions can explain the temperature dependence of the helical pitch. No assumption will be made on the shape of the molecules.     

Influence of the molecular structure of copper phthalocyanines on their ordering in thin films and photoluminescence and absorption spectra

Thin films consisting of copper phthalocyanine (CuPc) molecules and copper phthalocyanine molecular complexes with different structures on glass and glass-ceramic substrates are studied using reflectance anisotropy, photoluminescence, and photoconductivity (constant photocurrent method) spectroscopies. It is established that, in the studied films, the CuPc molecules and CuPc molecules containing peripheral phthalimide substituents are located in planes virtually parallel to the surface of the substrate. In thin films consisting of μ-peroxo dimer complexes, the angle between the CuPc molecular planes and the surface of the substrate is close to 90°. The thin films formed by CuPc molecules containing peripheral phthalimide substituents are characterized by the highest luminescence intensity in the range of ～ 1.12 eV and the lowest absorption intensity in the range of energies less than the band gap. These properties are explained by the lower concentration of non-radiative recombination centers in the film.     

Pulsed evaporator of an electrodynamic disperse suspension of particles

We consider the technique for obtaining electrodynamic disperse suspension of metal (Al, W, Cu) and dielectric (semiconductor) particles (SiO₂, Al₂O₃, CuO, Cu₂O) and its evaporation with the help of a diffusive electric discharge. The time dependences of current and integrated luminescence intensity in a pulsed electric discharge in a tube containing a film of a substance (Cu) of the electrodynamic disperse suspension are measured.     

Enhanced broadband light absorption in silicon film by large-size lumpy silver particles

Broadband light absorption enhancement in crystalline silicon thin-film solar cells by rear-located 400 nm lumpy silver particles has been studied, based on the theoretical simulations of 3D finite-difference time-domain method. By simulations, we have investigated the light scattering properties of 400 nm lumpy Ag particles and put it to silicon thin-film solar cells. In addition, the varying rear-located Ag particles coverage and two surface situations of silicon films, which could influence on the light absorption of solar devices, have also been comprehensively considered. The results have shown that rear-located 400 nm lumpy Ag particles would enhance the absorption in silicon films in a broadband range. And it has been proved that 20 % coverage density of rear-located Ag particles is optimal for improving the light absorption of smooth silicon thin-film solar devices. When we create rough surface on one or both sides of silicon films, the absorbed light would further increase, and the theoretical maximum enhancement is 15.1 % compared with the smooth silicon thin-film solar cell without Ag particles.     

Size effect on the optical and paramagnetic absorption of silver particles in a glass matrix

A study has been made of the optical absorption produced by small (10–100 Å) silver particles in a glass matrix. Measurements of the width of the absorption agree quite well with those calculated theoretically using the particle sizes estimated from electron microscopy, whilst the peak position of the absorption calculated for the smallest size particles does not seem to be so reliable. Contrary to the theoretical predictions of the quantum size effect in small metal particles and to experimental results obtained by other workers, no conduction electron spin resonance was observed from the silver particles at room temperature or at 7.5°K.     

A simplified model to predict the effects of aggregation on the absorption properties of soot particles

An exact electrostatics formulation for sphere clusters is used to predict the Rayleigh-limit radiative absorption properties of soot aggregates. In the near to mid IR wavelengths, it is shown that aggregation can result in absorption cross sections that are significantly larger than that predicted by an independent-sphere (Rayleigh–Gans) model. The relative increase in absorption increases with the number of spheres in the aggregate, and reaches an asymptote for aggregates containing 100–200 spheres. A simplified correlation is developed to predict the aggregate absorption cross section as a function of number of spheres and refractive index. Implications of the effects of aggregation on absorption and emission of thermal radiation by soot in flame and atmospheric environments are discussed.     

The energy and angular spectra of grey particles in high-energy hadron-nucleus interactions

A simple Monte Carlo model giving energy and angular spectra of the knocked out nucleons in the high energy hadron-nucleus interactions is described. The only input of the approach consists of some constants from the nuclear and high energy hadron-hadron phenomenology and without any adjustable parameters the model well reproduces substantial features of the experimental data.