Tetsuo Tsuchiya

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.

DIRECT CONVERSION OF TITANIUM ALKOXIDE INTO CRYSTALLIZED TIO2 (RUTILE) USING COATING PHOTOLYSIS PROCESS WITH ARF EXCIMER LASER

TiO2 (rutile) films have been successfully prepared by the coating photolysis process using ArF excimer laser irradiation at room temperature. The choice of the Ti-alkoxide type as the starting material and the effects of atmosphere on the product films have been studied by Fourier transformation infrared (FT-IR) and X-ray diffraction (XRD). When using Ti(O-i-C3H7)4 as the starting material, rutile films were obtained by the irradiation in a dry N2 atmosphere, whereas amorphous films were obtained by irradiation in air. When using Ti(OCH2CH(C2H5)-n-C4H9)4 as a starting material, rutile films were obtained by the irradiation even in the air atmosphere. Crystallization mechanism is also discussed.

Direct Conversion of Metal Acetylacetonates and Metal Organic Acid Salts into Metal Oxides Thin Films Using Coating Photolysis Process with An ArF Excimer Laser

Metal oxide films of TiO2, In2O3, ZrO2, ZnO, SnO2 and Fe2O3 have been successfully prepared by the coating photolysis process using ArF excimer laser irradiation at room temperature. When using metal acetylacetonates (acac) as the starting material, TiO2, In2O3 and ZrO2 were obtained with ArF laser irradiation at 50 mJ/cm2 at a repetition rate of 5 Hz for 5 min. When using Zn-acac, Fe, Sn, or In 2-ethylhexanoate as the starting material, a two-step process consisting of preliminary weak and sufficiently strong irradiation was found to be effective for obtaining ZnO, Fe2O3, SnO2 and In2O3 films.

Microstructural and electrical properties of La0.7Ca0.3MnO3 thin films grown on SrTiO3 and LaAlO3 substrates using metal-organic deposition

La0.7Ca0.3MnO3 (LCMO) thin films have been prepared on LaAlO3 and SrTiO3 (STO) (001) single-crystal substrates by the metal-organic deposition process. These films were characterized by transmission electron microscopy (TEM) and temperature dependence of the resistance R(T). The microstructure of the LCMO films and LCMO/substrate interfaces were investigated through cross-sectional TEM observations. High-resolution TEM (HRTEM) observations and electron-diffraction patterns demonstrate the (001) epitaxial growth on both the LAO and STO substrates. The local structure of the LCMO film depends on the type of substrate. HRTEM observations along the LCMO/STO interface display a good epitaxy throughout the entire film without any microstructural defects. On the contrary, in the LCMO film and in the region close to the LAO substrate, we note the presence of misfit dislocations and twins. The temperature coefficient of resistance (TCR) was calculated from the temperature dependence of the resistance measurements....

Low temperature growth of epitaxial La0.8Sr0.2MnO3 thin films by an excimer-laser-assisted coating pyrolysis process

The preparation of La0.8Sr0.2MnO3 (LSMO) films on a LaAlO3 (LAO) substrate has been investigated by an excimer-laser-assisted coating pyrolysis process (ELACPP) in the temperature range from 350 to 500°C. (00l) oriented LSMO films were successfully obtained by ArF laser irradiation at 100 mJ/cm2 in the substrate temperature range from 400 to 500°C. The films prepared at 500°C on the LAO substrate were found to be epitaxially grown based on X-ray diffraction (XRD) pole-figure measurements. The temperature dependence of the resistance of the LSMO film prepared at 400°C showed a semiconducting behavior. On the other hand, that prepared at 500°C showed a metallic behavior from 310 K to 100 K and the absolute magnitude of the resistivity of the film at 300 K was 2.6×10-2 Ωcm.

Selective deposition of anatase and rutile films by KrF laser chemical vapor deposition from titanium isopropoxide

Abstract Titanium oxide films were prepared by a KrF laser chemical vapor deposition technique from sublimated titanium isopropoxide at substrate temperatures (328–573 K), the laser repetition rates (10–100 Hz) and supply rates of the precursor (60–300 mg/h) on a quartz substrate under the fixed laser fluence of 450 J/m 2 . The deposits prepared were rutile and/or anatase in any experimental condition used. Low substrate temperature, low laser repetition rate, and high supply rate of the precursor is favorable to the rutile formation. Dependence of the rate of deposition per pulse on these factors and interrelations among these experimental conditions are discussed.

Preparation and Characterization of Epitaxial VO2 Films on Sapphire Using Postepitaxial Topotaxy Route via Epitaxial V2O3 Films

Epitaxial VO2 films were prepared on the C-planes of α-Al2O3 substrates by a metal organic deposition (MOD) process. It was difficult to obtain the single phase of (010)M-oriented VO2 films, in which the subscript M refers to the monoclinic indices, by the heat treatment of amorphous precursor films in the VO2-stable region after the pyrolysis of the coating solution. The product films consisted of discontinuous circular grains of 1–2 µm size on the substrate surface. Therefore, we prepared the (010)M-oriented epitaxial VO2 films using postepitaxial topotaxy (PET), that is, topotactic oxidation of (0001)-oriented epitaxial V2O3 films. First, epitaxial V2O3(0001) films were obtained by MOD starting with a vanadium naphthenate solution. Second, the epitaxial V2O3(0001) films were topotactically oxidized at 500 °C in an Ar–O2 gas mixture with pO2 = 10-4 atm to obtain (010)M-oriented epitaxial VO2 films. The epitaxial relationships were VO2(010)M ∥ α-Al2O3(0001) and VO2[100]M ∥ α-Al2O3[0110], [1010], [1100]. The VO2(010)M films exhibited metal–semiconductor transitions with hysteresis loops at 60–80 °C. The resistivity change before and after the transition of the VO2(010)M film oxidized for 6 h was three orders of magnitude.

Effective-Time of Pulsed Photothermal Heating for Polycrystalline Nucleation of Perovskite Oxide Films from an Amorphous Matrix

For making a photoinduced crystal growth method more universal, we have investigated the key parameters for polycrystalline nucleation from an amorphous matrix of LaMnO3 with focus on the pulsed photothermal heating time under excimer laser irradiation. We have clearly demonstrated that effective annealing time (teff) was very important for the crystallization under the excimer laser irradiation. The teff is defined as the time in which the temperature at the film surface increases over the effective annealing temperature for the crystallization of LaMnO3. The threshold of the teff value for initial crystal nucleation was evaluated to be approximately 60 ns for this material.

Rapid formation of black titania photoanodes: pulsed laser-induced oxygen release and enhanced solar water splitting efficiency

Solar energy is a key part of creating a sustainable society. Pulsed ultraviolet laser irradiation of titania films is a simple process for making oxygen-deficient black titania (TiO2−x) films that use the solar spectrum efficiently. TiO2−x photoanodes were obtained by KrF laser irradiation under low-vacuum conditions for several minutes. The TiO2−x film had a larger absorbance than pristine TiO2 in the visible light region, and it exhibited a substantial increase in photoelectrochemical water splitting under simulated solar light. The solar-to-hydrogen efficiency of the TiO2−x photoanode reached 0.52%, which was 2.6-fold higher than that of the pristine TiO2 photoanode. This rapid fabrication process for black titania photoanodes has great potential for industrial solar hydrogen production.

Low-Temperature Fabrication of Red Phosphor Ca0.997Pr0.002TiO3 Thin Film Using Excimer Laser Assisted Metal Organic Deposition

Ca0.997Pr0.002TiO3 thin films that show strong red luminescence were successfully prepared by an excimer laser assisted metal organic deposition (ELAMOD) process at temperatures from 25 to 400 °C. Laser irradiation induced an oxygen deficiency in the film. Oxygen annealing at 500 °C eliminated the oxygen vacancy and remarkably improved the emission intensity. The crystallinity of the film prepared by the ELAMOD exceeded that of the film prepared by a conventional thermal metal organic deposition (MOD) process at 900 °C. The photoluminescence emission of the film prepared by the ELAMOD process at 250 °C followed by oxygen annealing at 500 °C was stronger than that of the film fabricated by the thermal process at 900 °C.