Yoshie Ishikawa

Single-Crystalline Rutile TiO2 Hollow Spheres: Room-Temperature Synthesis, Tailored Visible-Light-Extinction, and Effective Scattering Layer for Quantum Dot-Sensitized Solar Cells

A general synthesis of inorganic single-crystalline hollow spheres has been achieved through a mechanism analogous to the Kirkendall effect, based on a simple one-step laser process performed at room temperature. Taking TiO(2) as an example, we describe the laser process by investigating the influence of experimental parameters, for example, laser wavelength, laser fluence/irradiation time, liquid medium, and concentration of starting materials, on the formation of hollow spheres. It was found that the size-tailored TiO(2) hollow spheres demonstrate tunable light scattering over a wide visible-light range. Inspired by the effect of light scattering, we introduced the TiO(2) hollow spheres scattering layer in quantum dot-sensitized solar cells and achieved a current notable 10% improvement of solar-to-electric conversion efficiency, indicating that TiO(2) hollow spheres are potential candidates in optical and optoelectronic devices.

Electrodeposition of TiO2 photocatalyst into nano-pores of hard alumite

Abstract TiO2 was electrodeposited into the pores of hard alumite (Al/Al2O3/TiO2) by alternative electrolysis in (NH4)2[TiO(C2O4)2] solution, where the alumite was prepared by anodic oxidation of aluminum in sulfuric acid (Al/Al2O3). When the electrolysis was carried out in an (NH4)2[TiO(C2O4)2] solution under ac bias for the Al/Al2O3, a cathodic current due to the reduction of H+ and/or H2O was observed at about −10 V in measurement of the Lissajous figure, leading to the deposition of TiO2. Consequently, the TiO2 was deposited during an increase in pH due to the electrochemical reduction reactions of H+ and/or H2O in the pores of the alumite. The deposited TiO2 was highly dispersed in the pores of the alumite. The prepared TiO2 in the pores (Al/Al2O3/TiO2) showed high photocatalytic activity for the decomposition of acetaldehyde compared to TiO2 deposited directly on an aluminum surface (Al/TiO2).

Preparation and investigation of the formation mechanism of submicron-sized spherical particles of gold using laser ablation and laser irradiation in liquids.

Results of very recent studies have shown that laser irradiation (LI) of colloidal nanoparticles (NPs) using a non-focused laser beam at moderate fluence transforms the NPs to submicron-sized spherical particles (SMPs). For this study, we applied this technique to prepare gold SMPs from source gold NPs prepared by laser ablation of a gold plate in an aqueous solution. Results show that SMPs were obtained from NPs in pure water, but a considerably large amount of the source NPs were sedimented without LI. On the other hand, SMPs were not obtained from NPs stabilized by 1 mM citrate. These findings indicate that the agglomeration of the source NPs prior to the laser-induced melting is important to obtain SMPs, although the sedimentation of the source NPs caused by considerable agglomeration should be reduced to obtain SMPs efficiently. A proper condition of the agglomeration tendency of the source NPs to prepare SMPs reducing the sedimentation of the source NPs was obtainable by simply adjusting the citrate solution concentration. Moreover, investigation of the temporal dynamics of the formation process of SMPs suggested that the agglomeration of the source NPs not only is controlled by citrate but also is induced by LI. LI brings about the decomposition and removal of citrate molecules on the surface of the source NPs, and cause the agglomeration of the source NPs dynamically; then it brings about the fusion of the agglomerated NPs.

Boron carbide spherical particles encapsulated in graphite prepared by pulsed laser irradiation of boron in liquid medium

B4C submicron particles were obtained by laser irradiation of B particles in ethyl acetate under atmospheric pressure and room temperature. Absorbed laser energy brought about B melting and decomposition of surrounding liquid medium molecules, leading to a reaction between the melted B and carbon species to form B4C. Moreover, the obtained B4C particles were encapsulated in a graphite layer. Such a graphite surface layer is useful for medical functionalization of particles. Thus, obtained B4C particles encapsulated in graphite are expected to be promising agents for boron neutron capture therapy.

Low-threshold and quasi-single-mode random laser within a submicrometer-sized ZnO spherical particle film

An unique random laser exhibiting quasi-single-mode and low lasing threshold is developed by a homogenized submicrometer-sized zinc oxide particle film dispersed with intentionally introduced polymer particles as point defects. Such unique random lasing is dominantly initiated at the defect sites, although multi-mode peaks with a collapsed broad emission spectrum are observed at the defect-free sites as in the conventional random lasers. Thus our proposed simple structure can possibly provide the controllability of lasing properties even in random structures.

Dye-sensitized solar cells based on anatase TiO2 nanocrystals exposing a specific lattice plane on the surface

Dye-sensitized solar cells (DSCs) using anatase TiO2 nanocrystals exposing a specific lattice plane on the surface were studied. It was found that dye adsorption strongly depends on the lattice plane exposed on the TiO2 nanocrystal surface, which greatly affects DSC performance. TiO2 nanocrystals exposing mainly the (010) plane have a higher dye adsorption capacity and a higher Voc for DSC than normal spherical nanocrystals. TiO2 nanocrystals with a large adsorption constant Kad can yield a high Jsc. The highest Jsc (20.6 mA/cm2) was achieved by using TiO2 nanocrystals with the specific lattice plane on the surface.Dye-sensitized solar cells (DSCs) using anatase TiO2 nanocrystals exposing a specific lattice plane on the surface were studied. It was found that dye adsorption strongly depends on the lattice plane exposed on the TiO2 nanocrystal surface, which greatly affects DSC performance. TiO2 nanocrystals exposing mainly the (010) plane have a higher dye adsorption capacity and a higher Voc for DSC than normal spherical nanocrystals. TiO2 nanocrystals with a large adsorption constant Kad can yield a high Jsc. The highest Jsc (20.6 mA/cm2) was achieved by using TiO2 nanocrystals with the specific lattice plane on the surface.

Characterization of metal-gate FinFET variability based on measurements and compact model analyses

A FinFET compact model, which provides physical representation of measurement data, was developed and was successfully applied to the characterization of sate-of-the-art metal-gate (MG) FinFETs. By combining the transistor size measurement and the model parameter calibration, the Vth variation of the MG FinFETs was analyzed into structure-based (TSi, LG) and material-based (gate work-function) variations for the first time. In addition, the extracted variations were incorporated into the compact model, and FinFET SRAM variability for hp-32-nm node was predicted.

Relationships between Cell Parameters of Dye-Sensitized Solar Cells and Dye-Adsorption Parameters

The performance of dye-sensitized solar cells (DSCs) is affected strongly by sensitizer-dye adsorption behavior on TiO(2) nanocrystal electrode. This study reports quantitative relationships between DSC cell performance parameters and dye-adsorption parameters for the first time. We discovered a logarithmic relationship between short-circuit photocurrent density (J(sc)) and dye-adsorption equilibrium constant on TiO(2) surface, and a linear relationship between open-circuit potential (V(oc)) and dye-adsorption density on TiO(2) surface for DSCs. These relationships provide a convenient method for forecasting the performance of TiO(2) nanoparticles for DSCs from the dye-adsorption parameters, and also indicate future directions for the development of high-performance TiO(2) nanoparticles for DSCs.

Fabrication and characterization of core/shell structured TiO2/polyaniline nanocomposite

A novel core/shell structured TiO(2)/polyaniline nanocomposite was fabricated by grafting aniline on aminobenzoate monolayer that is chemically adsorbed on the TiO(2) nanocrystal surface. The formation and nanostructure of the nanocomposite were investigated by FT-IR and UV-Vis spectra, TEM, FE-SEM, and TG-DTA analysis. Adsorption of aminobenzoate on the TiO(2) surface is an effective method to obtain the uniform nanocomposite. The thickness of polyaniline layer coating on the TiO(2) nanocrystal surface can be controlled in a range of 2-5 nm by this method. A photoelectrochemical study was carried out on the TiO(2)/polyaniline nanocomposite, and found that polyaniline in the nanocomposite acted as a visible-light sensitizer in a photoelectrochemical reaction. The sensitization effect increased with increasing binding strength between polyaniline and TiO(2). A dye-sensitized solar cell with a short circuit current density of 0.19 mA/cm(2) and an open circuit voltage of 0.35 V was fabricated by using the TiO(2)/polyaniline nanocomposite film as a sensitized electrode.

Electrodeposition of TiO2 photocatalyst into porous alumite prepared in phosphoric acid

Abstract TiO 2 was electrodeposited into the pores of alumite by alternative electrolysis in (NH 4 ) 2 [TiO(C 2 O 4 ) 2 ] solution (Al/Al 2 O 3 /TiO 2 ), where the alumite was prepared by anodic oxidation of aluminum in phosphoric acid solution. The applied ac voltage to deposit TiO 2 was high in the present alumite, compared with that in the case of sulfuric acid solution, because the alumite formed in phosphoric acid solution has a barrier layer thicker than that of the alumite formed in sulfuric acid solution. The particle size of the deposited TiO 2 was less than 1 nm. The Al/Al 2 O 3 /TiO 2 prepared in this study showed high phorocatalytic activity for the decomposition of acetaldehyde.