Keisaku Kimura

Ionic conductivity of small-grain polycrystals of silver iodide

Abstract Small particles of AgI with various average size (140–680 nm) have been prepared by a gas-evaporation method. The powder X-ray diffraction patterns show that they are mixture of γ- and β-phases, and the mass fraction of the latter is roughly estimated at 20–25%. The room temperature conductivity of a polycrystalline pellet of small AgI particles shows enhancement by decreasing particle size, and the conductivity of 1.4×10 −4 Ω −1 cm −1 has been observed in 140 nm-grain AgI polycrystal. The overall activation energy for conduction varies from 0.38 to 0.28 eV, depending on the average size of the particles.

Effect of sample transparency in powder diffractometry with Bragg–Brentano geometry as a convolution

The effect of transparency and finite thickness of the sample on the peak profile in powder diffractometry with Bragg–Brentano geometry is treated as a convolution with an asymmetric aberration function. The formula of the aberration function and a practical method for numerical calculation of the convolution are proposed. The model function for the total profile is given by triple convolution of the pseudo-Voigt function with asymmetric functions based on vertical (axial) divergence, horizontal (equatorial) divergence and sample transparency. The validity of the model profile function is examined by fitting the Cu Kα X-ray diffraction profile of diluted lanthanum hexaboride (LaB6) standard samples (SRM660) of 0.5 mm thickness, the transparency of which is varied by mixing with different amounts of starch; all the parameters that may affect the shape of the profile function are treated as fixed parameters. Even in the case of heavily distorted profiles of highly transparent samples with the inverse linear absorption coefficients μ−1 = 0.34 and 1.19 mm, experimental profiles are fairly well reproduced by the model function, typically within several % in R factor. It is also demonstrated that the lattice constants of the transparent samples are precisely evaluated by applying this model function.

Palladium carbide nanoparticles by gas flow reaction synthesis

Nanoparticles of palladium carbide, a metastable phase with carbon atoms on interstitial sites of metallic lattice, were synthesized by a single process, which allows palladium metallic nanoparticles formed by vapor condensation in flowing argon carrier gas to immediately come in contact with acetone vapor. The average particle size observed by transmission electron microscopy is 5 nm and the geometric standard deviation of the distribution is 1.5.

Size dependence of the quantum yield of photoluminescence from silicon nanocolloids

We have prepared several nanometer-sized silicon colloids in the range from 3.7 to 9.8 nm with a constant weight density 1 mg/ml. The blue-green emission is found to be independent of size contrast to its intensity. The absolute quantum yield as a function of size is determined. From the proposed model that combines surface as well as volume effects, the emission is proved to be from a surface trapped site. The energy transfer efficiency from volume to the site is almost 100% for the 3.7 nm particle.

Instability of gold nano-islands in several organic media

Abstract The UV-VIS absorption spectroscopy and transmission electron microscopy (TEM) of Au nano-island films, deposited on quartz glass and on amorphous carbon substrate by a sputtering method were applied to study stability or instability of gold nanoparticles in twelve organic liquids with different dielectric constants. The morphology of island films was determined by both TEM and scanning tunneling microscopic observations. The surface plasmon peak characteristic of gold nano-particles showed clear peak shift, peak intensity enhancement and peak width broadening corresponding to the dielectric constants of the liquid. It was also found that the Au island particles on the carbon substrate were destabilized for some kinds of liquids such as benzyl alcohol and dimethylsulfoxide. The balancing of the interactions among Au particle, substrate and liquid materials is crucial to this finding.

Blue Luminescence from Silicon Nanoparticles Suspended in Organic Liquids

We have prepared several nanometer-sized silicon colloids in organic liquids in the range from 3.7 to 9.8 nm with a constant weight density of 1 mg/ml by a gas evaporation technique. The blue–green luminescent energy was found to be independent of size, in contrast to its intensity and optical absorption, which showed a clear size effect. Special emphasis is placed on the advantage of using a colloidal system: controllability of mass density in a unit volume, isolation of each particle, selection of wide band-gap substances, capability of absolute quantum efficiency, and easy surface modification. As an example of the above advantages, we have determined the absolute quantum yield as a function of size. From the quantum yield thus derived and the proposed model that combines surface as well as volume effects, experimentally obtained parameters such as the diffusion velocity of an electron–hole pair and the initial flight distance of this pair are found to be consistent with those obtained from other data.

RATE PROCESS OF THE COAGULATION OF NANOPARTICLES

Nanometer-sized gold particles dispersed in organic liquids coagulate under the influence of addition of salt or illumination of Mie resonance irradiation. It is derived that the van der Waals attractive force can be enhanced by the excitation of surface plasmon, hence the rate of coagulation is accelerated through the DLVO (Derjaguin, Landau, Verway, Overbeek) potential among the particles. The coagulation rate and the stability ratio are calculated within a framework of DLVO theory.

PREPARATION AND SURFACE LAYER MODIFICATION OF SILICON NANOPARTICLES DISPERSED IN 2-PROPANOL

Silicon nanoparticles dispersed in 2-propanol were prepared by using an arc plasma with gas flow method in a new designed home-made apparatus. The particles are composed of silicon crystal core covered by oxidized amorphous silicon shell. The composition of the particle surface layer can be modified by preparing the sample in different atmosphere. The particles can be also obtained with different core composition and different size which we need.

A novel method for large-scale synthesis of AgI nanoparticles

Thiol-derivatised I–VII nanoparticles of AgI (7–16 nm) are prepared in large quantities by the reaction of silver nitrate with potassium iodide containing 1-thioglycerol in aqueous solution.

Electrocrystallization, Crystal Structure, and Solid State Properties of Halogen-Bridged One-Dimensional Compound, {[Ni(en)2Br](ClO4)2)∝, Having an Elongated Ni ••• Ni Distance

Abstract Two crystal forms (α and β) of a novel halogen bridged one-dimensional NiIII-Br-NiIII compound, {[Ni(en)2Br](ClO4)2}∝ (en=C2H8N2), have been prepared by electrochemical oxidation. X-ray crystal structure analysis of the α form revealed that a bridging Br ion is located on the midpoint between two Ni atoms and the Ni-Br distance of 2.640(1) A is significantly elongated by introducing a bulky ClO4 − ion as a counter anion. An average Ni-Br distance of 2.693(2) A for the β form can be estimated from the lattice parameter along the chain. X-ray photoelectron spectra indicate that both forms have the NiIII-X-NiIII structure. Magnetic susceptibility data for both forms show strong antiferromagnetic coupling (J=-1700) between electronic spins (S=1/2) localized on the NiIII on the linear chain.