Formation of gallium nitride particles during the two-stage chemical vapor process

The effects of the reaction temperature in the first stage T_I on the formation and the luminescent property of both the seed and the grown particles were investigated in the region from 1050 to 1200 °C for the two-stage vapor-phase synthesis of GaN particles. The reaction efficiency of vaporized Ga and NH₃ to form the seed particles increased with increasing T_I up to about 1150 °C, where the maximum value of about 70% was obtained. Further raising T_I caused a decrease of the efficiency. The X-ray diffraction and the photoluminescence (PL) measurements indicated both of the crystal quality and the luminescent property of the seed particle were improved with increasing T_I. On the other hand, the PL intensity of the particles grown on the seed in the second stage decreased with increasing T_I. This difference in the dependence was explained in terms of the morphology of the grown particles. The mechanism of particle formation during these processes was also discussed based on the results.     

Growth of high-quality ZnO single crystals by seeded CVT using the newly designed ampoule

The high-quality ZnO single crystals were grown by seeded chemical vapor transport (CVT) in a newly designed ampoule using carbon as a transport agent. The well-faceted crystal of about 5×5×5 mm³ can be grown reproducibly. Secondary ion mass spectroscopy (SIMS) analysis, X-ray rocking curve (XRC) and photoluminescence (PL) measurements demonstrate that the grown single crystal is of high purity and high crystallinity.     

Electrochemical Detection of Free Chlorine Using Ni Metal Nanoparticles Combined with Multilayered Graphene Nanoshells

An electrochemical detection of free chlorine using carbon‐metal (C?M) composite powder, with a nickel‐metal nanoparticle combined with a multilayered graphene nanoshell (Ni metal@multilayered graphene) as the main component, synthesized from CH₄ via multimode microwave‐assisted catalytic decomposition, was studied. Morphological analysis of the C?M composite powder was performed by TEM–EDX and Raman spectroscopy. The C?M composite powder was packed in a porous microelectrode (PME), and its electrochemical activity with respect to free chlorine was evaluated using a potential sweep method. The C?M composite powder exhibited a sufficient activity against free chlorine. A current based on the reduction of free chlorine was observed in the potential < around+0.3 V vs. Ag/AgCl. A linear relationship was observed between the current and the concentration.     

Fabrication of platinum particles by intense, femtosecond laser pulse irradiation of aqueous solution

Platinum nano-particles were directly fabricated through molecular dissociation process induced by tightly focused femtosecond laser pluses in hydrogen hexachloroplatinate (IV) hexahydrate (H₂PtCl₆·6H₂O) aqueous solution. After irradiation, it was found that UV-visible absorption spectrum of the solution was changed and a large number of small platinum particles were synthesized. The variation of absorbance in the spectrum and the yield the particle synthesis depended on the concentration of the solution. The most effective condition for particle synthesis was 0.1 wt%. Black precipitates of platinum particles were observed in the bottom of the vessel after irradiation in some cases. The dispersibility of the particles was greatly improved by the addition of polyvinylpyrrolidone (PVP) as a dispersant, and no precipitates were found in the solution with 1.0 × 10⁻² wt% PVP. Consequently, highly monodispersed platinum nano-particles with the mean size of about 3 nm were successfully fabricated.     

Isomerization and fluorescence characteristics of sterically hindered azobenzene derivatives

We report synthesis and isomerization behaviors of sterically hindered azobenzene derivatives (1 and 2) with decyloxy and hydroxy groups, respectively, and their fluorescence enhancement under UV light irradiation characterized by means of absorption and fluorescence spectroscopy measurements. Upon irradiation of as-prepared solution (1) with UV light (∼200 mJ/cm²) a cis-rich photostationary state was reached. Obviously different from 2 showing very fast thermal cis-to-trans isomerization within 2 min, slow cis-to-trans thermal back isomerization of 1 with a long alkyl chain at ambient temperature was observed on the time scale of weeks. In contrast to no striking changes in absorption and fluorescence spectra of compound 2, the azobenzene 1 showed green fluorescence upon prolonged irradiation with UV light (about 3-8 J/cm² exposure doses), although both the initial trans-rich and cis-rich states of azobenzene molecules were not fluorescent in solution. The stability of fluorescence efficiency caused by drying and redissolving processes was examined.     

Solution properties of ionomers. I. Counterion effect

The effect of counterions on the solution properties of two types of ionomers, one based on sulfonated polystyrene and the other based on styrene–methacrylic acid copolymer, was studied by viscosity and light scattering measurements. It was found that the order of counterion binding of ionomers in a polar solvent and the order of aggregation of ionomers in a low-polarity solvent were the same for the same ionomer system. However, the order for the sulfonated ionomer was Li < Na < K < Cs, whereas that for the carboxylated ionomer was the opposite. This can be explained by a difference in desolvation during anion–cation interaction and by considering site-binding in a polar solvent and the association of ion pairs in a low-polarity solvent. These findings for ionomer systems are parallel to the association behavior of small ions in water, cation affinity in crosslinked resins, and counterion binding of polyelectrolytes in water.     

Novel 4-phenoxy-2-(1-piperazinyl)quinazolines as potent anticonvulsive and antihypoxic agents

A series of 4-phenoxy-2-(1-piperazinyl)quinazolines was synthesized and examined for anticonvulsive and antihypoxic activities. Many of the compounds exhibited potent anticonvulsive activity comparable to that of carbamazepine or phenytoin. Among them, 4-phenoxy-2-(4-propyl-1-piperazinyl)quinazoline (5w) was selected as the most promising candidate antiepileptic drug with few side effects. It seemed that potent anticonvulsive activity was a prerequisite for potent antihypoxic activity.     

An analysis of odd-mass rare-earth nuclei using angular momentum projection

A systematic analysis of positive-parity rotational states in odd-mass rare-earth nuclei is presented. The theory used is microscopic in the true sense and conserves both the angular momentum and the particle number as the projection technique is applied. The hamiltonian contains the quadrupole pairing interaction (in addition to the conventional (monopole) pairing and Q · Q forces) which plays an essential role in odd-mass as well as in doubly-even nuclei. Agreement between theory and experimental data is excellent.     

Spatial structure and stability based on random walks

A general expression for a recursion formula which describes a random walk with coupled modes is given. In this system, the random walker is specified by the jumping probabilities P⁺ and P^– which depend on the modes. The transition probability between the modes is expressed by a jumping probabilityR ^(ij) (orr _ij). With the aid of this recursion formula, spatial structures of the steady state of a coupled random walk are studied. By introducing a Liapunov function and entropy, it is shown that the stability condition for the present system can be expressed as the principle of the extremum entropy production.On leave of absence from Tohoku University, Department of Applied Science, Faculty of Engineering, Sendai, 980 Japan.