Ta_3N_5 is one of the potential candidates for visible-light-driven photocatalyst in water splitting. In this study, Ta_3N_5 crystal layers were successfully fabricated on Ta substrates via two- and one-step processes including flux coating method. In two-step fabrication, high-quality nano-/microtextured NaTaO_3 crystal layers were directly fabricated on a Ta substrate by flux coating method using NaNO_3, and the NaTaO_3 crystal layers were subsequently transformed to Ta_3N_5 crystal layers by heating under NH_3 flow. The individual Ta_3N_5 crystals retained the original sizes and shapes of NaTaO_3 crystals but became highly porous after nitridation. In one-step fabrication, well-developed Ta_3N_5 crystals were directly grown on Ta substrates by heating under NH_3 with Na compounds. When Na_2CO_3-NaCl mixture was used as the flux, prism-like Ta_3N_5 crystals were uniformly grown.

View full abstract

Lithium titanate (Li_4Ti_5O_<12>) crystal layers, useful as anode material for lithium-ion rechargeable batteries, were successfully grown on surfaces of lithium-ion conducting glass via an atmospheric pressure plasma-assisted flux coating (APP-FC) method. First, TiO_x layers have been fabricated on a lithium-ion conducting glass substrate by plasma-enhanced chemical vapor deposition using a titanium tetraisopropoxide (TTIP) and oxygen. Then, TiO_x layers were converted to Li_4Ti_5O_<12> crystal layers by APP-FC method. In addition, the form and thickness of the crystal layers depended on the growth conditions such as the starting composition and an atmospheric pressure N_2 plasma irradiation time.

View full abstract

Carbon nanotube (CNT) has great properties such as mechanical strength, electric current carrying ability and thermal conductivity so that it has been developed for applications such as polymer composite material as well as electronic devices. However, CNT tends to agglomerate due to van der Waals forces so that it can't exhibit the above characteristics. Therefore, it has been studied about chemical modification of CNT to improve the affinity with the solvent. In this study, we try surface treatment of MWCNT using solution plasma process (SPP) which is plasma reaction field in the solution for modifying CNT surface with functional group and improvement dispersibility in the water.

View full abstract

Lithium ion conductor research is determined by an increased demand of energy and by the necessity to develop stable electricity devices for energy accumulation. Recently a great attention was focused on solid type lithium ion batteries which use an inorganic solid electrolyte material with excellent heat and chemical attract resistance. However, generally, the ionic conductivity of a solid electrolyte is low, and has not reached a practical used level. In recent years, the sulfide system solid electrolyte attracts much attention as a material which shows high ion conductivity. In particular, Li_<10>GeP_2S_<12> has been reported to show the highest ion conductivity of 12 mS/cm. The degree of lithium ion conduction in a solid originates in the crystal structure of the material. In this research, the study is made to replace various elements by an ion radius and an electron arrangement paying attention to the above-mentioned material, and the relation between the crystal structure change and the ion conductivity was investigated.

View full abstract

The development of alternative catalyst with the economical production cost and high catalytic activity instead of Pt-based catalyst for fuel cells is good challenge. It is well known that Fe-N_4/C possesses the catalytic activity for oxygen reduction reaction, with high potential for utilization as cathode. Here, the Fe-N/C particles were synthesized using various precursors by solution plasma process (SPP). In this method, the selection of precursor can control the elemental composition of the synthesized Fe-N/C which affects to the catalytic activity. Pyridine, aniline, pyridine/aniline, and pyridine/triazine as the selected precursors were discharged to form N-carbon particles. In addition, the incorporation of Fe was achieved by the chemical complex of Fe ions. The synthesized Fe-C/N particles were characterized to confirm the elemental composition using elemental analysis. The structural analysis was done by XRD and TEM. Furthermore, the electrocatalytic activity was investigated using cyclic voltammetry under the O_2 and N_2 saturated conditions.

View full abstract

In the past, the bandgap energy of indium nitride had been assumed to be approximately 1.9 eV. In recent years, with the development of the crystal growth technology, it was revealed that the bandgap energy of indium nitride was approximately 0.7 eV. The difference in the bandgap energy was due to the fact that the film obtained by the conventional process had become indium nitride film doped with a small amount of oxygen. On the other hand, bandgap energy can be varied over 1 eV by doping with a small amount of oxygen. The film obtained by the conventional process was not discussed in detail as concerning the role of oxygen because doping with oxygen was not a purpose. Therefore, in this study, we have prepared indium nitride films by changing the amount of oxygen and tried to control of the bandgap energy change.

View full abstract

High-quality CuInS_2 (CIS) crystals were grown by the flux method using a chloride flux. CIS is generally used in absorption layers of thin-film photovoltaic cell due to their high energy conversion efficiency and high absorption coefficient. High-quality CIS crystals with low defect density and thermal strain are expected to high photon-to-current conversion efficiency. Flux growth is one of the preferred methods because the crystal can grow in an unconstrained fashion and therefore develop facets, resulting in high quality crystals. In this study, high-quality CIS crystals were successfully grown from the chloride flux. The morphology of the synthesized crystals was dependent on the growth conditions such as the holding temperature.

View full abstract

GdBa_2Cu_3O_y superconducting thin films show a high critical current density when the crystal grains are oriented in all directions. In this study we investigated the influence of film growth factors on the crystal orientation of the thin films during the film formation by a pulsed laser deposition technique. Substrate temperature and the oxygen pressure were varied from 680℃ to 800℃ and from 0.1Torr to 1.0Torr, respectively. It was found that the c-axis orientation was dependent of the substrate temperature, in particular; the films had highest proportions of c-axis grains at 760℃. Proportions of a-axis of the films increased at lower temperature and the oriented films cannot be obtained at high temperature. In addition it was shown that a-and-b-axes orientations were found dependent of oxygen pressure; the films formed at 0.1Torr and 0.4Torr aligned in-plane. The condition of achieving highest degrees of orientation is 760℃ and low oxygen pressure.

View full abstract

We introduced BaHfO_3 (BHO) artificial pinning centers in YBa_2Cu_3O_7 (YBCO) thin films by a solution method and their crystal structures and superconducting property were examined. The films were calcined at 430℃ in oxygen atmosphere and crystallized at 780℃ in low oxygen atmosphere. As the results of XRD, peaks corresponded to BHO were observed in the films. No large degradation of crystalline are recognized on the YBCO films after BHO introducing. Superconducting transition temperature, T_C, and critical current density, J_C, were more than 90K and 3.5 MA/cm^2, respectively, which were as high as YBCO films with BaZrO_3(BZO). Consequently, it was proved that YBCO films with BHO could be fabricated by solution method.

View full abstract

A new β phase Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy was developed for biomedical materials. Since TNTZ alloy is bioinert, several studies have been reported grow the bioactive oxide layer on TNTZ surface. In this study, the nanotube arrays were fabricated on TNTZ surface by a anodization, and their structural and crystallographic were investigated. The crystallized TNTZO nanotube arrays in anatase phase were obtained after annealing at 500℃ for 3h though as-anodized TNTZO was amorphous. The photocatalytic activity of the crystallized TNTZO nanotubes was evaluated by degradation of gaseous acetaldehyde in air under UV light irradiation, and degradation of gaseous acetaldehyde was observed.

View full abstract