Determination of the Disperse Composition of a PbO Suspension Containing Aggregates of Particles of Lamellar Shape by the Laser-Polarimetry Method

The results of measurements of the scattering matrix at a wavelength of 0.63 μm in the range of scattering angles of 10°–155° are presented for an aqueous suspension of lead oxide containing particles of plate form and their aggregates of monomers with dimensions of ~5 nm. The results of the measurements are compared with the results of calculations for axially symmetric scatterers (ellipsoids of rotation, cylinders). It is shown that the presence of aggregates affects the scattering properties of such a medium. The results of reconstructing the distribution of particles of a disperse medium in sizes from the measurements data of the scattering matrix are presented. The reconstruction of the distributions was carried out by solving the problem of optimizing the sum of the squared deviations of the experimental and calculated values of matrix elements in the framework of the model of axially symmetric scatterers. It is shown that the distribution of particles by sizes is more accurately reconstructed by minimizing the sum of the squares of the deviations for the sum of the diagonal elements. The obtained distribution is compared with the distribution measured by the method of dynamic light scattering.     

Flame propagation of nano/micron-sized aluminum particles and ice (ALICE) mixtures

Flame propagation of aluminum–ice (ALICE) mixtures is studied theoretically and experimentally. Both a mono distribution of nano aluminum particles and a bimodal distribution of nano- and micron-sized aluminum particles are considered over a pressure range of 1–10 MPa. A multi-zone theoretical framework is established to predict the burning rate and temperature distribution by solving the energy equation in each zone and matching the temperature and heat flux at the interfacial boundaries. The burning rates are measured experimentally by burning aluminum–ice strands in a constant-volume vessel. For stoichiometric ALICE mixtures with 80 nm particles, the burning rate shows a pressure dependence of r_b = aPⁿ, with an exponent of 0.33. If a portion of 80 nm particles is replaced with 5 and 20 μm particles, the burning rate is not significantly affected for a loading density up to 15–25% and decreases significantly beyond this value. The flame thickness of a bimodal-particle mixture is greater than its counterpart of a mono-dispersed particle mixture. The theoretical and experimental results support the hypothesis that the combustion of aluminum–ice mixtures is controlled by diffusion processes across the oxide layers of particles.     

Synthesis of CdS quantum dots by mechanochemical reaction

2 + Na₂S → CdS + 2NaCl induced by mechanical milling resulted in the formation of CdS particles with an average diameter of < 8 nm. The average particle size was controlled within the range of 4 to 8 nm by varying the size of the grinding media. The onset energy of optical absorption showed a blue shift with decreasing particle size. Received: 29 August 1997/Accepted: 25 September 1997     

纳米银六角阵列在掺氧氮化硅中的局域表面等离激元共振特性仿真

通过COMSOL Multiphysics 和 Lumerical FDTD solution对不同尺寸纳米银六角阵列在非晶态掺氧氮化硅(a-SiN_x:O)介质中的局域表面等离激元共振(LSPR)特性进行仿真, 计算结果表明半径为25 nm的纳米银六角阵列形成的局域表面等离激元(LSP)与厚度为70 nm的a-SiN_x:O的蓝光发射(460 nm)的共振效果最为显著, 随着纳米银颗粒尺寸的增大其消光共振峰红移. 在460 nm波长激发下半径为25 nm的纳米银阵列在a-SiN_x:O中的极化强度和表面极化电荷的分布模拟证明了该阵列在460 nm激发下形成的LSP为偶极子极化模式, 通过对该尺寸的纳米银阵列的LSP 在a-SiN_x:O中的最强垂直辐射空间计算, 获得了银颗粒上方a-SiN_x:O的最佳厚度为30 nm, 仿真结果对硅基蓝光发射器件(450–460 nm)的设计提供了重要的理论参考.     

Optimized method of dispersion of titanium dioxide nanoparticles for evaluation of safety aspects in cosmetics

Nanoparticles agglomerate when in contact with biological solutions, depending on the solutions’ nature. The agglomeration state will directly influence cellular response, since free nanoparticles are prone to interact with cells and get absorbed into them. In sunscreens, titanium dioxide nanoparticles (TiO₂-NPs) form mainly aggregates between 30 and 150 nm. Until now, no toxicological study with skin cells has reached this range of size distribution. Therefore, in order to reliably evaluate their safety, it is essential to prepare suspensions with reproducibility, irrespective of the biological solution used, representing the above particle size distribution range of NPs (30–150 nm) found on sunscreens. Thus, the aim of this study was to develop a unique protocol of TiO₂ dispersion, combining these features after dilution in different skin cell culture media, for in vitro tests. This new protocol was based on physicochemical characteristics of TiO₂, which led to the choice of the optimal pH condition for ultrasonication. The next step consisted of stabilization of protein capping with acidified bovine serum albumin, followed by an adjustment of pH to 7.0. At each step, the solutions were analyzed by dynamic light scattering and transmission electron microscopy. The final concentration of NPs was determined by inductively coupled plasma-optical emission spectroscopy. Finally, when diluted in dulbecco’s modified eagle medium, melanocytes growth medium, or keratinocytes growth medium, TiO₂–NPs displayed a highly reproducible size distribution, within the desired size range and without significant differences among the media. Together, these results demonstrate the consistency achieved by this new methodology and its suitability for in vitro tests involving skin cell cultures.     

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48 nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450 °C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe₂O₃. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.     

Preparation and luminescent properties of phosphor MGd2(MoO4)4: Eu (M=Ca, Sr and Ba)

Intense red emitting phosphors MGd₂(MoO₄)₄: Eu³⁺ (M=Ca, Sr and Ba) have been synthesized by the simple sol-gel technique. The formation processes and the phase impurity of phosphors are characterized by thermogravimetry-differential thermal analysis (TG-DTA) and power X-ray diffraction (XRD). The narrower size distribution and the regular shape of the phosphor particles are also measured by Field emission scanning electronic microscopy (FE-SEM). Photo-luminescent properties of the phosphors are performed at room temperature. Their excitation spectra present strong absorption at 395 nm near-UV light and 465 nm blue light, which match well with commercial LED chips. The phosphors exhibit satisfactory and excellent red light dominated by 616 nm and their photoluminescence intensity is about 3-4 times stronger than that of phosphor YAG under the 465 nm excitation. In addition, the optimal concentrations of Eu³⁺ for phosphors MGd₂(MoO₄)₄ (M=Ca, Sr and Ba) have also been determined.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Fatigue in precipitation hardened materials: a three-dimensional discrete dislocation dynamics modelling of the early cycles

Three-dimensional dislocation dynamics (DD) fatigue simulations in precipitation hardened metals is a major challenge in terms of numerical development. Several precipitate configurations have been investigated with an original treatment of precipitate–dislocation interactions and a parallelized DD code. In grains containing single-sized shearable particles (r _p?=?160?nm), strain is localized in clear bands where the precipitates are totally sheared-off. The fatigue behaviour involves an initial hardening followed by severe cyclic softening and significant surface slip irreversibility. In the presence of large single-sized particles (r _p?=?400?nm), the persistent slip band (PSB) structure is accompanied by highly reversible surface displacements. Slip dispersion originates from Orowan loops that have little effect on the mechanical response. The mechanical behaviour of a bimodal distribution is intermediate between the two above cases with the above microstructural features coexisting within the same grain. Unlike in the monomodal large-particle case, where all the particles retain their initial strength, some of the large particles of the bimodal distribution undergo a significant strength reduction.     

Luminescence properties of a new green emitting Eu2+-doped barium chlorosilicate phosphor

A new intense green light-emitting phosphor, the Eu²⁺-doped (BaO–BaCl₂–SiO₂) phosphor system, was synthesized at 800°C by the conventional high-temperature solid-state reaction. Its structure and luminescence properties were investigated by using thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), diffuse reflection spectra, photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The photoluminescence spectrum reveals that this phosphor can be efficiently excited by near-ultraviolet (UV) light and blue light in the wavelength region covering 280 and 480 nm, which perfectly matches the emission wavelength of near-UV light-emitting diodes (LEDs). It emits an intense green light peaking at 502 nm, which is promising to develop possible applications for white LEDs.     

A study of oleic acid-based hydrothermal preparation of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Nearly monodisperse, well crystalline, superparamagnetic CoFe₂O₄ nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure, as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase, with size of the particles (5–8 nm) controlled by polarity-driven precipitation into water phase). As-prepared particles were hydrophobic due to coating by oleic acid. Further modification with dimercaptosuccinic acid led to water-dispersible particles with hydrodynamic diameter of 20 nm. Prepared particles were investigated by TEM, XRD, ICP-AES, light scattering, SQUID magnetometry, and Mössbauer spectroscopy.     

Comparison of the efficiency of titanium(IV) and iron(III) oxide nanoparticles as mediators in suppression of bacterial growth by radiation of a blue (405 nm) light-emitting diode

The effect of blue (405 nm) radiation of a light-emitting diode in combination with titanium(IV) and iron(III) oxide nanoparticles on S. aureus 209 P, S. simulans, and D. hominis bacteria is studied. It is shown that, upon irradiation of bacteria by blue (405 nm) light, Fe₂O₃ nanoparticles have a stronger (by 5–30%) antibacterial effect than TiO₂ nanoparticles.     

Excitation wavelength dependence and magnetic field effect on aerosol particle formation from a gaseous mixture of carbon disulphide and glyoxal

Upon excitation of carbon disulphide (CS₂) molecules under UV light irradiation at 313?nm a gaseous mixture of CS₂ and glyoxal deposited sedimentary aerosol particles only. The nucleation process of the aerosol particles was investigated by measuring the He–Ne laser light intensity scattered by the aerosol particles formed under light irradiation at 313?nm, and the chemical structure of the sedimentary particles was analysed by measuring the FT-IR and X-ray photoelectron spectra. On application of a magnetic field of up to 5?T, the nucleation process was decelerated and the chemical species originating from CS₂ were less abundant. The results were compared with those obtained under visible light irradiation at 435.8?nm reported previously. Chemical reactions between CS₂ and glyoxal molecules, which were responsive to the magnetic field, are discussed briefly.     

Effect of the “inversion” of a scattering medium in layers of close-packed titanium dioxide nanoparticles

The features of the behavior of the diffuse transmission of layers of close-packed titanium dioxide nanoparticles in the visible and near infrared spectral ranges with an increase in the volume fraction f of the particles in a layer have been analyzed. It has been found that an increase in f for layers of small particles (about 25 nm) with a relatively low volume fraction (0.20–0.25) is accompanied by the expected decrease in diffuse transmission. At the same time, an increase in f for layers of large particles (about 100 nm) with a volume fraction of 0.45–0.50 results in a strong increase in transmission. The described phenomenon has been interpreted in terms of the concepts of inverse scattering systems, where the main scattering centers are air nanocavities in a TiO₂ matrix rather than TiO₂ particles in an air matrix.     

Zinc oxide nanoparticles reinforced conducting poly(aniline-co-p-phenylenediamine) nanocomposite

Zinc oxide (ZnO) nanoparticles were synthesized by thermal decomposition method and formation of composite with conducting copolymer via in situ chemical oxidative polymerization. Transmission electron microscopy showed that the nanoparticles with an average diameter of 15–25?nm were dispersed in the copolymer matrix. The comonomer molecules were adsorbed on the surface of ZnO particles and then polymerized to form core–shell nanocomposite. The obtained nanocomposite showed a significant improvement in the thermal behavior as indicated by thermogravimetric analysis. The nanocomposite was also confirmed by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and X-ray diffraction. Room temperature conductivity of nanocomposite was higher than the value obtained for the pure copolymer. Photocatalytic activity of the nanocomposite was evaluated by measuring the degradation of methylene blue dye under UV irradiation.     

Red, yellow, green and blue – four-color light from a single, aperiodically poled LiTaO3 crystal

We demonstrate simultaneous quasi-continuous wave generation of red, yellow, green and blue coherent radiation based on quadruple quasi-phase matching (QPM) frequency upconversion from a single, aperiodically poled LiTaO₃ (APPLT) crystal with a diode-pumped Nd:YVO₄ dual-wavelength laser oscillating at 1342 and 1064 nm. We designed and prepared an APPLT crystal, which can provide four pertinent reciprocals for simultaneous quadruple QPM processes. Namely, frequency doubling of 1342 nm generates red light at 671 nm, sum-frequency mixing of 1342 nm and 1064 nm produces yellow light at 593 nm, frequency doubling of 1064 nm achieves green light at 532 nm and sum-frequency mixing of 1342 nm and 671 nm obtains blue light at 447 nm. PACS 42.65.Ky; 42.79.Nv; 42.55.Xi; 42.72.Bj     

Gallium-doped indium oxide nanoleaves: Structural characterization,growth mechanism and optical properties

The novel two-dimensional (2-D) Ga-doped In₂O₃ nanoleaves are synthesized by a simple one-step carbonthermal evaporation method using Cu–Sn alloy as the substrates. Two basic parts construct this leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetric distribution in relation to the trunk. The Ga–In–O alloy particles are located at or close to the tips of the central trunks and serve as catalysts for the central trunk growth by the self-catalytic vapor–liquid–solid (VLS) mechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunk can be explained by vapor–solid (VS) mechanism. The room-temperature photoluminescence (PL) measurement of this nanoscaled Ga-doped In₂O₃ transparent conducting oxide (TCO) detected two blue peaks located at 432 nm and 481 nm, respectively, which can be used by Ru-based dye and indicates potential application in dye-sensitized solar cells (DSSCs). The successful preparation of this novel 2-D Ga-doped In₂O₃ nanoleaves not only enriches the synthesis of TCO materials, but also provides new blocks in future architecture of functional nano-devices.     

Enhanced Near‐Infrared Shielding and Light Scattering Using Surface‐Roughened Hybrid Hollow Microparticles Synthesized with Polymer and TiO2@Al(OH)3 for Cosmetic Applications

Some materials and their micro‐/nanostructures are explored to shield near‐infrared (NIR) light. However, the structural role of polymeric matrices in terms of the sensitivity to NIR light and the scattering/absorption characteristics of particles bearing inorganic colloids lack understanding. To understand this issue further, a polymer–inorganic hybrid microparticle is synthesized, where submicrometer‐sized TiO₂ core‐thin aluminium hydroxide shell colloids (TiO₂@Al(OH)₃) are dispersed in a roughened polymer hollow particle matrix. They exhibit higher light extinction at NIR frequencies and higher light scattering efficiencies in the NIR regions compared to hybrid solid microparticles and a simple mixture of inorganic and polymer hollow microparticles. Owing to these characteristics, a cosmetic formulation containing the roughened hybrid hollow microparticles effectively suppresses the increase in the temperatures of artificial skin upon the illumination of a simulated sunlight, without displaying skin whitening which is caused by including much inorganic colloids in the formulation. The present results are helpful to those who manipulate the optical characteristics of inorganic particles whose geometries are hardly tailored. The results are also practically helpful to those who want to block NIR light by reducing the amount of inorganic particles.     

Positron annihilation spectroscopy characterization of effect of intermetallic nanoparticles on accumulation and annealing of vacancy defects in electron-irradiated Fe–Ni–Al alloy

The effect of intermetallic nanoparticles like Ni₃Al and nanoparticles of an Fe-rich bcc phase on the evolution of vacancy defects in an fcc Fe–34.2 wt% Ni–5.4 wt% Al model alloy under electron irradiation at elevated temperatures (423 and 573 K) was investigated using positron annihilation spectroscopy. Nanosized (1–8 nm) particles, which are homogeneously distributed in the alloy matrix, cause a several-fold decrease in the accumulation of vacancies as compared to their accumulation in a quenched alloy. This effect depends on the size and the type of nanoparticles. The effect of the nanoparticles increases when the irradiation temperature increases. The irradiation-induced nucleation and the growth of intermetallic nanoparticles were also observed in an alloy pre-aged at 1023 K under irradiation at 573 K. Thus, a quantum-dot-like positron state within ultrafine intermetallic particles, which we revealed earlier, allows control of the evolution of coherent precipitates like Ni₃Al, along with vacancy defects, during irradiation and subsequent annealing. Possible mechanisms of the absorption of point defects by nanoparticles are discussed.     

Effect of Particle Size and Phase Composition of Titanium Dioxide Nanoparticles on the Photocatalytic Properties

Titanium dioxide (TiO₂) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl₄) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO₂ nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO₂ nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO₂ nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.