The effects of thermal annealing in NH3 -ambient on the p-type ZnO films

Thermal annealing in NH₃-ambient was carried out to form p-type ZnO films. The properties were examined by X-ray diffraction (XRD), Hall-effect measurement, photoluminescence (PL), and secondary ion mass spectrometry (SIMS). Electron concentrations in ZnO films were in the range of 10¹⁵–10¹⁷/cm³ with thermal annealing in NH₃-ambient. The activation thermal annealing process was needed at 800 C under N₂-ambient to obtain p-type ZnO. The electrical properties of the p-type ZnO showed a hole concentration of 1.06×10¹⁶/cm³, a mobility of 15.8 cm²/V s, and a resistivity of 40.18 Ω cm. The N-doped ZnO films showed a strong photoluminescence peak at 3.306 eV at 13 K, which is closely related to neutral acceptor bound excitons of the p-type ZnO. The incorporation of nitrogen was confirmed in the SIMS spectra.     

Facile S(N)2 reaction in protic solvent: quantum chemical analysis

We study the effects of protic solvent (water, methanol, ethanol, and tert-butyl alcohol) and cation (Na+, K+, Cs+) on the unsymmetrical SN2 reaction X- + RY --> RX + Y- (X = F, Br; R = CH3,C3H7;Y = Cl, OMs). We describe a series of calculations for the S(N)2 reaction mechanism under the influence of cation and protic solvent, presenting the structures of pre- and postreaction complexes and transition states and the magnitude of the activation barrier. An interesting mechanism is proposed, in which the protic solvent molecules that are shielded from the nucleophile by the intervening cation act as a Lewis base to reduce the unfavorable Coulombic influence of the cation on the nucleophile. We predict that the reaction barrier for the S(N)2 reaction is significantly lowered by the cooperative effects of cation and protic solvent. We show that the cation and protic solvent, each of which has been considered to retard the SN2 reactivity of the nucleophile, can accelerate the reaction tremendously when they interact with the fluoride ion in an intricate, combined fashion. This alternative S(N)2 mechanism is discussed in relation to the recently observed phenomenal efficiency of fluorination in tert-alcohol media [Kim, D. W.; et al. J. Am. Chem. Soc. 2006, 128, 16394].     

Shape-controlled synthesis of silver sulfide nanocrystals by understanding the origin of mixed-shape evolution

The shape of silver sulfide nanomaterials was successfully controlled by understanding the origin of the mixed-shape problem.     

Novel application of Leuckart-Wallach reaction for synthesis of tetrahydro-1,4-benzodiazepin-5-ones library

A novel and efficient strategy has been developed to synthesize privileged tetrahydro-1,4-benzodiazepines with excellent yields and purities; this synthetic pathway was established by the revitalization of the Leuckart-Wallach (LW) reaction via solid-phase synthesis.     

Establishment of a fabrication method for a long-term actuated hybrid cell robot

We developed a novel method to fabricate a crab-like microrobot that can actuate for a long period in a physiological condition. The microrobot backbone was built with a biocompatible and elastic material-polydimethylsiloxane (PDMS)-by using a specially designed 3D molding aligner, and consisted of three strips of PDMS "legs" connected across a "body." Cardiomyocytes were then plated on the grooved top surface of the backbone, resulting in a high concentration of pulsating cells. These key techniques enabled the microrobot to walk continuously for over ten days. The performance of our crab-like microrobot was measured at an average velocity of 100 microm s(-1), and the estimated total distance it travelled was 50 m over a one-week period. Thus, we have demonstrated for the first time a walking robot that exhibited reliable and long-term actuation performances.     

Highly sensitive and selective chemosensor for Hg2+ based on the rhodamine fluorophore

A novel tren-based tripodal chemosensor 1 bearing a rhodamine and two tosyl groups was synthesized and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of a Hg2+ ion to a CH3CN solution of 1 gave a visual color change as well as significantly enhanced fluorescence, while other ions including Pb2+, Zn2+, Cu2+, Ca2+, Ba2+, Cd2+, Co2+, Mg2+, Ag+, Cs+, Li+, and Na+ induced no or much smaller color/spectral changes, which constituted a Hg2+-selective fluorescent chemosensor (OFF-ON).     

Rhodamine-based Hg2+-selective chemodosimeter in aqueous solution: fluorescent OFF-ON

[reaction: see text] N-(Rhodamine-6G)lactam-N'-phenylthiourea-ethylenediamine (1) was developed as a fluorescent and colorimetric chemodosimeter in aqueous solution with a broad pH span (5 approximately 10) and high selectivity toward Hg2+ but no significant response toward other competitive cations, such as Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Ca2+, Mg2+, K+, Na+, etc. The Hg2+-promoted ring opening of spirolactam of the rhodamine moiety induced cyclic guanylation of the thiourea moiety, which resulted in the dual chromo- and fluorogenic observation (OFF-ON).     

Spin-triplet pairing instability of the spinon fermi surface in a U(1) spin liquid

Recent experiments on the organic compound kappa-(ET)2Cu2(CN)3 have provided a promising example of a two-dimensional spin liquid state. This phase is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi surface due to singular interaction processes with twice-the-Fermi-momentum transfer. We find that under certain circumstances the pairing instability occurs in odd-orbital-angular momentum or spin-triplet channels. Implications to experiments are discussed.     

Sonolysis of chlorinated compounds in aqueous solution

To examine the reaction rates of sonochemical degradation of aqueous phase carbon tetrachloride, trichloroethylene and 1,2,3-trichloropropane at various temperatures, power intensities, and saturating gases, the batch tests were carried out. The degradations of chlorinated hydrocarbons were analyzed as pseudo first order reactions and their reaction rate constants were in the range of 10(-1)-10(-3)/min. The reaction was fast at the low temperature with higher power intensity. Also, the reaction went fast with the saturating gas with high specific heat ratio, high solubility and low thermal conductivity. The main mechanism of destruction of chemicals was believed the thermal combustion in the bubble.