Papers by Author: Masaki Tanemura

Abstract: To improve the controllability of the fabrication of carbon aerogels, the effects of the concentration of the reactant (RF%) on the structural properties of organic resorcinol formaldehyde (RF) gel and the effects of the carbonization temperature on nanostructure of carbon aerogels were discussed. The concentration of the reaction was turned from 5%,10%,20%,30%,40%,50%,55% and 60% to prepare the samples. The RF aerogels were carbonized at temperature of 700, 900 and 1050. The shrinkage and nitrogen gas adsorption were measured. Experimental results showed that the structural stability of the organic RF aerogel can be improved by decreasing the shrink in drying process and increasing the condensation of reactant in the starting solution to a certain value, such as 55%. The ordered pore size distribution of carbon aerogels with less structure defects is able to be produced through the effective particle fusing at the carbonization temperature as high as 1050.

Abstract: Mixed matrix membranes (MMM) combine useful molecular sieving properties of inorganic fillers with the desirable mechanical and processing properties of polymers. The current trend in polymeric membranes is the incorporation of filler-like nanoparticles to improve the separation performance. Most MMM have shown higher gas permeabilities and improved gas selectivities compared to the corresponding pure polymer membranes. Carbon nanotubes based mixed matrix membrane was prepared by the solution casting method in which the functionalized multiwalled carbon nanotubes (f-MWNTs) were embedded into the polyimide membrane and the resulting membranes were characterized. The effect of nominal MWNTs content between 0.5 and 1.0 wt% on the gas separation properties were looked into. The as-prepared membranes were characterized for their morphology using field emission scanning electron microscopy (FESEM) and Transmission Electron Microscopy (TEM). The morphologies of the MMM also indicated that at 0.7 % loading of f-MWNTs, the structures of the MMM showed uniform finger-like structures which have facilitated the fast gas transport through the polymer matrix. It may also be concluded that addition of open ended and shortened MWNTs to the polymer matrix can improve its permeability by increasing diffusivity through the MWNTs smooth cavity.

Abstract: To have a fundamental understanding on the principle of carbon aerogels when it is used as electrode materials in power battery, the effects of density and structural properties on the electrical conductivity of carbon aerogels was investigated in this paper. Carbon aerogels with different density were prepared via adjusting the chemical conditions of the primary solution. The morphology of carbon aerogels were observed by field emission scanning electron microscopy (FE-SEM). Experimental results show that the electrical conductivity of carbon aerogels is ranged from 10-6 Ω/cm to 10 Ω/cm, and that not only the density but also the carbon particle size and porosity of carbon aerogels effect the transport property greatly. With the increasing of the density the electrical conductivity of carbon aerogels increases. This indicates that larger particle size and lower porosity of the nano-structure lead to higher conductivity.

Abstract: A compact angle-resolved secondary ion mass spectrometer (AR-SIMS) with a special geometrical configuration, composing of a differentially pumped micro-beam ion-gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer was applied to measure angular distribution (AD) of secondary ions ejected from VN by oblique 3 keV Ar+ sputtering at room temperature. AD of V+ was almost identical with that of N+, strongly suggesting that Gibbsian segregation did not take place during sputtering. Since the angular dependence of VN+/V+ and V2 +/V+ intensity ratios was independent of that of N+ and V+ intensities, VN+ and V2 + dimer ions were generated via the “as such” direct emission process.

Abstract: Toward the tailored growth of carbon nanotubes (CNTs), CNT growth using hydrocarbon ion beams at the ion energy of 150 eV and the ion current densities of 10 ∼ 165 μA/cm2 was challenged at various growth temperatures. Fibrous protrusions with an amorphous nature grew at a low ion current density, whereas highly crystallized multi-wall CNTs were synthesized at high ion current densities. The higher the growth temperature and the ion current density, the smaller the CNT diameter. Similar to the conventional PECVD-grown CNTs, they grew via the so-called “tip-growth mode.”

Abstract: Photochromic material Ag-TiO2 thin films are fabricated on quartz substrate by dual -target helicon magnetron sputtering. The phototchromic behavior is investigated for the sample loaded with 90% Ag. Spheres, ellipsoids and polyhedra shape of Ag particles with wide range size (5∼100 nm) are dispersed in the TiO2 amorphous matrix observed by transmission electron microscopy. The spectral hole burned by the irradiation of laser at the wavelength 532 nm can be explained by a particle-plasmon-assisted electron transfer from Ag nanoparticles to TiO2 and subsequent trapping by adsorbed molecular oxygen. Moreover, the mechanism of the slow recovery after photochromism is suggested as a slow thermal release of electrons from oxygen trapping centers and subsequent capture into the Ag nanoparticles.

Abstract: Transparent indium-doped ZnO (IZO) films with low In content (<6at%) were fabricated through radio-frequency (rf) helicon magnetron sputtering. Formation of In-Zn-O solid solution was confirmed by X-ray diffraction (XRD) patterns. Incorporation of indium into ZnO films enhances the optical transmission in the visible wavelength. The optical band-gaps slightly increase from 3.25eV (ZnO) to 3.28eV (In0.04Zn0.96O) and to 3.30eV (In0.06Zn0.94O) due to Burstain-Moss effect. The Urbach tail parameter E0, which is believed to be a function of structural disorder, increases from 79meV (ZnO), to 146meV (In0.04Zn0.96O), and to 173meV (In0.06Zn0.94O), which is consistent with increase of Full-Width Half-Maximum (FWHM) in corresponding XRD patterns. Decreasing in crystal quality with increasing indium concentration is also confirmed by photoluminescence spectra.

Abstract: RF (Resorcinol-Formaldehyde) aerogels and carbon aerogels were prepared through the sol-gel method following the routes of polymerization, gelation, supercritical drying and pyrolysis processes. The influence of fabrication parameters on the textural structure of the samples, e.g., specific surface area, pore size, and pore size distribution, etc., were systematically investigated. With a decrease in the R/F molar ratio, or an increase in the catalyst content within a limited range, the porosity of the nanostructure materials increases. The optimal temperature of pyrolysis for RF aerogel was investigated by TGA (Thermogravimetric Analysis).

Abstract: The photocatalytic effects of 4 samples, which TiO2 layer uniformly coated on Al fiber, are evaluated by NOx removal. An anatase TiO2 coating with good crystal quality and high Ti content exhibits the best photocatalytic effect on NOx removal. It is coincidence with the results of XRD, XPS results for 4 samples. The photocatalytic ability is enhanced by the introduction of H2O2 due to the formation of large amount OH radicals.

Abstract: We have prepared titania aerogel (=AG) embedded by NiB nano-clusters by sol-gel method, immersion of the prepared wet gel into the NiB dispersed solution, and the subsequent super critical drying (=SCD). The AG was characterized by X-ray diffraction (XRD), a transmission electron microscopy (TEM), and a fourier transform infrared spectrophotometer (FT-IR). XRD and selected area electron diffraction (SAED) patterns assured the formation of TiO2 anatase phase. TEM observation reveled the composition of TiO2 crystallites with about 4 nm in size. Catalyst performance for the ground sample was confirmed by chemical reaction of oxidation of benzene at low temperature, and the difference in catalyst performance between TiO2 AGs with and without the embedded NiB nano-clusters has been examined.