Takayuki Ishizaka

Luminescence properties of Tb3+ and Eu3+-doped alumina films prepared by sol-gel method under various conditions and sensitized luminescence

Abstract Rare earth ion (Tb 3+ and Eu 3+ )-doped alumina films were prepared by the aqueous sol-gel method under various conditions. The influences of the OH groups (phonon relaxation) and rare earth ion concentration (cross-relaxation) on luminescence were examined. In regard to the former relaxation, at treatment temperature above 600°C, reciprocal lifetime decreased with OH concentration, and below 500°C, decreased markedly and nonlinearly. On the other hand, in regard to the latter relaxation, there was negligible effect on luminescence for these doped films. The quantitative treatment was tried to lifetime considering these influences. Tb 3+ and Eu 3+ co-doped alumina films showed enhanced Eu 3+ luminescence by the energy transfer from Tb 3+ to Eu 3+ . Eu 3+ luminescence intensity increased with a greater Tb 3+ concentration.

Photo-properties of rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films prepared by the sol–gel method

Abstract Rare earth ion (Er 3+ , Eu 3+ and Sm 3+ )-doped alumina films have been prepared by the sol–gel method, using AlCl 3 -derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol–gel-derived alumina matrices gave a high-dopant concentration (∼15 mol% per alumina).

Preparation of Multilayered Film of Polyimide Nanoparticles for Low-K Applications

In order to reduce dielectric constant of polyimide, preparation of porous films assembled by polyimide nanoparticles was investigated. We utilized the electrophoretic deposition of polyimide nanoparticles to prepare porous low dielectric constant (low-k) films possessing voids between particles. The films thickness was controlled in the range of 500 nm ∼ 5 μm by changing the dispersion concentration and applied voltage. Porous morphologies were confirmed by SEM observation. As a result, dielectric constant of the film decreased to 2.32, 14% lower than that of the bulk polyimide film, due to the introduction of air voids into the matrix. This is the first report showing a promising approach with high processability for porous low-k polyimide films.

Preparation of refractory nitride fibers by thermal decomposition of transition metal (Ti, Nb) alkoxide-cellulose precursor gel fibers in NH3 atmosphere

Precursor gel fibers have been prepared by extruding cellulose acetate spinning solutions into transition metal (Ti, Nb, Ta) acetone solution as a coagulation bath. Gel formation must be due to the coordination of metal to OH and CO groups on the pyranose ring. The resultant gel fibers have been converted into nitride fibers by pyrolyzing the precursor in NH3 gas flow at temperatures lower than for powder processing. The precursor gel can give a molecular scale mixture of metal and carbon sources. NbN fiber gave a superconductance at around 13 K.

Intensity-controllable luminescence of Eu3+-doped polyimide nanoparticles by UV irradiation and heat-treatment

The intensity-controllable luminescence of Eu3+-doped polyimide (PI) nanoparticles by UV irradiation and thermal treatment is reported. In this system, it was observed that the luminescence intensity of Eu3+ ions increased with increasing UV irradiation time, whereas intensity decreased with the elevation of thermal treatment temperature. It was estimated that the mechanism of the above phenomena are based on a reversible change in an energy transfer probability from PI to Eu3+ due to the UV irradiation and thermal treatment.

Alumina coating on quartz glass and nickel substrates using aqueous sol derived from AlCl3 · 6H2O

The thick alumina films (0.2–0.5 μm) were prepared on quartz glass and nickel substrates by a dipping method using an alumina sol derived from an aqueous AlCl3 solution. The hardness of this coating was compared to those of similarly coated substrates that had been heat-treated at various temperatures. The hardness of the alumina coating increased with increasing heat-treatment temperature. This sol gave crack-free and well-coated substrates that could be heat-treated to temperatures up to 800°C. This may have been due to the formation of an amorphous mixed oxide interface layer between the alumina films and the substrates. At temperatures higher than 900°C, problems with the coating started to appear because the oxide layer formed into α-alumina accompanying evolution of stress in the interface.

Chapter 7:Efficient Transformation of Biomass-derived Compounds into Different Valuable Products: A “Green” Approach

In this work, supercritical carbon dioxide (scCO2), and scCO2/H2O were investigated for the processing of biomass-derived compounds such as 5-hydroxymethylfurfural (5-HMF), furfural and tetrahydrofurfuryl alcohol (THFA) into a vast array of fuel and non-fuel related chemicals. Higher solubility of reactant gasses in scCO2 results in an acceleration of the reaction rate and enhancement of the product selectivity. As a reaction medium, scCO2 offers promise to play a role in the conversion of 5-HMF to linear alkane, which relies heavily on hydrogen concentration. Furthermore, 5-HMF can be successfully converted to 2,5-dimethylfuran (a fuel additive) with the highest selectivity (100%) in ascCO2/H2O mixture. In the presence of H2O, scCO2 creates an acidic environment and contributes to improving the selectivity of 2,5-dimethylfuran. Similarly, furfural also produces 2-methylfuran through the hydrogenation/hydrogenolysis of the C–O bond. 1,5-pentanediol, which is used as a monomer in the polyester industry, could be conveniently obtained with 91% selectivity from THFA in scCO2 under the homogeneous conditions of a CO2–H2-substrate. Hence, the remarkable advantage of the present catalytic system has confirmed the potential utilisation of alternative “green” solvents in the conversion of different biomass based compounds.

Fabrication of Polyimide Porous Nanostructures for Low-k Materials

The processing speeds of microchips continue to increase as integration densities increase in the semiconductor industry. When the device size is decreased, the so-called resistance– capacitance (RC) delay and the crosstalk noise between metal interconnects offset any gain in chip performance. To avoid these undesirable phenomena, lower dielectric insulating layers must be employed. In the near future, it will be need to develop dielectric materials with ultralow dielectric constants (ultralow-k: k < 2.0), and a replacement dielectric for carbon-doped silicon dioxide (SiOC) will be required [1]. In addition, high-thermal stability, good adhesion to metals and chemical stability are also important requirements for the interlayer dielectrics. Polyimides (PIs) are among the most promising candidates for use as next-generation interlayer dielectrics because of satisfying all above-mentioned requirements. Indeed, PIs have been widely employed in the fields of microelectronics applications such as substrate of flexible printed circuitry boards, insulating layers in multilevel very-large-scale integrated (VLSI) circuits and buffer coatings in electronic packages. However, the dielectric constant (k) is about 2.4~3.0 even in fluorinated PIs [2-7], which are insufficient for the requirement of ultralow-k materials (k < 2.0).