Enhanced effective mass in doped SrTiO3 and related perovskites

The effective mass is one of the main factors determining the Seebeck coefficient and electrical conductivity of thermo-electrics. In this ab-initio LDA-GGA study the effective mass is estimated from the curvature of electronic bands by one-band-approximation and is in excellent agreement with experimental data of Nb- and La-doped SrTiO₃. It is clarified that the deformation of SrTiO₃ crystals has a significant influence on the bandgap, effective electronic DOS-mass and band-mass, but the electronic effect due to the e_g-band flattening near the Γ-point due to Nb-doping up to 0.2 at% is the main factor for the effective mass increase. Doping of La shows a linear decrease of the effective mass; this can be explained by the different surroundings of A- and B-sites in perovskite. Substitution with other elements such as Ba on the A-site and V on the B-site in SrTiO₃ increases the effective mass as well.     

Experimental and theoretical investigations of isomerization reactions of ionized acetone and its dimer

Ionization dynamics of acetone and its dimer in supersonic jets is investigated by a combination of experimental and theoretical techniques, both of which have recently been developed. In experiments, the neutral and the cationic structures are explored by infrared predissociation spectroscopy with the vacuum-ultraviolet photoionization detection schemes. Reaction paths following the one-photon ionization of the acetone monomer and its dimer have been studied by the joint use of several theoretical methods including the ab initio molecular dynamics, the global reaction route mapping, the intrinsic reaction coordinate, and the artificial force induced reaction calculations. Upon one-photon ionization, the dimer isomerizes to the H-bonded form, in which the enol cation of acetone is bound to the neutral molecule, while this enolization is energetically forbidden in the acetone monomer. The enolization of the dimer cation occurs through a two-step proton-transfer from the methyl group of the ionized moiety, and is catalyzed by the neutral moiety within the dimer cation.     

Preparation of hollow titania and strontium titanate spheres using sol–gel derived silica gel particles as templates

A facile approach, based on polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloidal templates and hydrothermal treatment, is presented for the formation of hollow titania (TiO₂) and strontium titanate (SrTiO₃) spheres. Monodispersed silica gel particles were prepared by the sol?Cgel method and adopted as core templates. Deposition of a water-soluble titanium complex, titanium (IV) bis(ammoniumlactato)dihydroxide (TALH), on the silica gel particles was carried out via the layer-by-layer assembly technique. Hollow spheres were successfully formed from the core?Cshell particles. The silica gel particles used as core templates dissolved during hydrothermal treatment because of the particles?? undeveloped siloxane network. In addition, the hydrothermal treatment induced crystallization of the hollow shells. Therefore, the hydrothermal treatment played two roles; removal of the silica templates and crystallization of the hollow shells. When deionized water was used, hollow TiO₂ spheres were obtained. Hollow SrTiO₃ spheres could also be formed when an aqueous solution of Sr(OH)₂ was used. The approach presented here could be exploited as a novel and sustainable approach for the fabrication of a range of different inorganic hollow spheres.     

Theoretical verification of nonthermal microwave effects on intramolecular reactions

There have been a growing number of articles that report dramatic improvements in the experimental performance of chemical reactions by microwave irradiation compared to that under conventional heating conditions. We theoretically examined whether nonthermal microwave effects on intramolecular reactions exist or not, in particular, on Newman-Kwart rearrangements and intramolecular Diels-Alder reactions. The reaction rates of the former calculated by the transition state theory, which consider only the thermal effects of microwaves, agree quantitatively with experimental data, and thus, the increases in reaction rates can be ascribed to dielectric heating of the solvent by microwaves. In contrast, for the latter, the temperature dependence of reaction rates can be explained qualitatively by thermal effects but the possibility of nonthermal effects still remains regardless of whether competitive processes are present or not. The effective intramolecular potential energy surface in the presence of a microwave field suggests that nonthermal effects arising from potential distortion are vanishingly small in intramolecular reactions. It is useful in the elucidation of the reaction mechanisms of microwave synthesis to apply the present theoretical approach with reference to the experiments where thermal and nonthermal effects are separated by screening microwave fields.     

Functional monomers and polymers. LXXXVI. Photochemical reactions on synthetic polymers with pendant thymine bases: Effect of solvents

Photodimerization of thymine bases present on the side chain of acryloyl and methacryloyl-type polymers was studied in dimethyl sulfoxide, dimethylformamide, and dimethyl sulfoxide—ethylene glycol mixture. Quantum efficiencies for photodimerization and quenching with isoprene were influenced by the solvents. The self-association of thymine bases estimated from their ultraviolet (UV) spectra and intrinsic viscosity were related to the effect of solvent on the photodimerization.     

Selective-precursor reducing route to cobalt nanocrystals and ferromagnetic property

Cobalt nanocrystals were prepared by controlled chemical route at mild condition through selective-precursor reducing synthesis. Nanorod bundles and three-dimensional (3D) dendritic nanocrystal networks of Co were prepared by selecting different precursors. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) technologies. Field-emission scanning electron microscopy (FE-SEM), SEM, and TEM images indicate the nanorod bundles mainly consist of nanorods with the diameter of 70 nm. In 3D dendritic nanocrystal networks there are numerous secondary and sub-secondary branches were grown at right angles on each main stem. Room temperature magnetic measure of the Co samples demonstrates much enhanced ferromagnetic property, which might be attributed to their organization of specific shape. The possible formation mechanism of the cobalt nanocrystals with different morphologies was also discussed.     

Fabrication of compositionally graded thin films by gravity-assisted pulsed laser ablation

A compositionally graded thin film of FeSi₂ was fabricated by a gravity-assisted pulsed laser ablation (GAPLA) system. By this method, a compositionally graded structure was successfully produced under a gravity field of 5400 G. We demonstrate that the atomic fraction of Fe, the heavier component of the thin film measured by scanning electron microscope/energy dispersive X-ray (SEM-EDX), showed increasing spatial distribution with the direction of gravity. We found that optimal laser fluence exists to give a thin film having the largest possible spatial compositional gradient. We found that surface energy density on the substrate surface is the key parameter to control the composition distribution. Furthermore, the ratio of Fe/Si of the film did not match that of the target. This result shows that the Si component is selectively etched during the film-forming process. Relatively high laser fluence as well as a very narrow space between the target and the substrate are essential to etch the film once it is deposited, in order to re-ionize and etch Si selectively while gravity accelerates both Fe and Si particles to the direction of gravity. We hypothesize that this process accounts for both the change in the stoichiometry and the formation of composition distribution.     

Laser ablation of liquid surface in air induced by laser irradiation through liquid medium

The pulse laser ablation of a liquid surface in air when induced by laser irradiation through a liquid medium has been experimentally investigated. A supersonic liquid jet is observed at the liquid–air interface. The liquid surface layer is driven by a plasma plume that is produced by laser ablation at the layer, resulting in a liquid jet. This phenomenon occurs only when an Nd:YAG laser pulse (wavelength: 1064 nm) is focused from the liquid onto air at a low fluence of 20 J/cm². In this case, as Fresnel’s law shows, the incident and reflected electric fields near the liquid surface layer are superposed constructively. In contrast, when the incident laser is focused from air onto the liquid, a liquid jet is produced only at an extremely high fluence, several times larger than that in the former case. The similarities and differences in the liquid jets and atomization processes are studied for several liquid samples, including water, ethanol, and vacuum oil. The laser ablation of the liquid surface is found to depend on the incident laser energy and laser fluence. A pulse laser light source and high-resolution film are required to observe the detailed structure of a liquid jet.     

Optical emission spectroscopy of thin film fabrication by pulsed laser ablation under high-gravity

We carried out the thin film deposition of iron silicide by pulsed laser ablation (PLA) on a sapphire substrate, which was placed on a high-speed rotating titanium disk. The deposited thin film exhibited a continuous composition gradient. We investigated how the continuous composition gradient was attained, because the strength of the gravity field in our experiment was far below that in the experiment on bulk crystalline compounds. In the present study, we obtain the spatial distribution of several species in the PLA plume of FeSi₂ by using an intensified charge-coupled device (ICCD) camera.     

The role of tetrahydrobiopterin in catalysis by nitric oxide synthase

Electronic structure calculations show that the cofactor H4B can be a key factor in a proton transfer relay in nitric oxide synthase, and that 4-amino-H4B cannot fulfill this role.