Toshiya Kumagai

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.

Preparation of Epitaxial Pb(Zr, Ti)O3 Thin Films on Nb-Doped SrTiO3 (100) Substrates by Dipping-Pyrolysis Process

Epitaxially grown Pb(Zr, Ti)O3 (PZT, Pb:Zr:Ti=1:0.52:0.48) thin films were prepared on Nb-doped SrTiO3 (100) substrates by dipping-pyrolysis process with metal naphthenates used as starting materials. The alignments of the films were investigated based on X-ray diffraction (XRD) θ–2θ scans, β scans (pole figures), and asymmetric ω–2θ scans (reciprocal-space maps). Epitaxial films with smooth surfaces were obtained by heat treatment of prefired films at 600°–750° C; a film heat-treated at 750° C showed the strongest peak intensities in the XRD θ–2θ scans. These PZT films were found by reciprocal-space map analysis to consist of the c-axis-oriented tetragonal phase.

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.

Effect of substrate material on the crystallinity and epitaxy of Pb(Zr,Ti)O3 thin films

Abstract Pb(Zr,Ti)O3 thin films (Pb:Zr:Ti=1:0.52:0.48) were prepared on various single-crystal substrates via dipping-pyrolysis process by use of metal naphthenates as starting materials. The alignments of these films were examined by X-ray diffraction (XRD) θ–2θ scans and β scans (pole figures). The films grown on Nb-doped SrTiO3, MgO or LaAlO3 showed an epitaxial relationship with substrates after heat treatment at 750°C, while those grown on sapphire and Si wafers exhibited polycrystalline or amorphous characteristics. Epitaxial films on SrTiO3 and LaAlO3 were found to consist of a c-axis oriented tetragonal phase, to minimize the lattice misfit with the substrates. These epitaxial films exhibited very smooth surfaces by SEM and AFM observations. In addition, the fluctuation of in-plane alignment was significantly dependent on the lattice-misfit values.

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.

Effects of Heat Treatment Conditions on the Critical Current Densities of Ba2YCu3O7-y Films Prepared by the Dipping-Pyrolysis Process

The effects of temperature and atmosphere on the BYCO formation reaction of BaCO3, Y2O3 and CuO, prepared by the pyrolysis of metal acetylacetonate solution, were examined by TG-DTA, XRD and resistivity measurement. This reaction was found to proceed readily below 900°C under low oxygen partial pressures. Superconducting Ba2YCu3O7-y films with Tc,zero\cong90 K and Jc(77 K)=300–400 A/cm2 were prepared by the dipping-pyrolysis process using the above solution through heat treatments at 820°–880°C under controlled low oxygen partial pressures of ρ(O2)=1×10-3–2×10-4 atm followed by O2 annealing.

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....

Synthesis and Surface Acoustic Wave Property of Aluminum Nitride Thin Films Fabricated on Silicon and Diamond Substrates Using the Sputtering Method

C-axis oriented aluminum nitride (AlN) thin films with a thickness of 1 µm were prepared by reactive DC magnetron sputtering on polycrystalline diamond substrates at a substrate temperature of 623 K. The average surface roughness (Ra) of the AlN thin films was less than 2 nm obtained by locating the diamond substrates at a position of 100 mm from the aluminum target. The full width at half maximum (FWHM) of the rocking curve for the AlN(002) peak determined by X-ray diffraction analysis was about 0.2°. The surface acoustic wave (SAW) structures were completed by the deposition of aluminum electrodes on the as-deposited AlN surfaces. The SAW characteristics of an interdigital transducer (IDT)/AlN/diamond structure were investigated. The phase velocity and coupling coefficient were 10,120 m/s and 0.3%, respectively.

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.

Preparation of epitaxial V2O3 films on C-, A- and R-planes of α-Al2O3 substrates by coating-pyrolysis process

Abstract Epitaxial films of vanadium(III) oxide V2O3 were prepared on the C-, A-, and R-planes of α-Al2O3 substrates by a coating-pyrolysis process. The final heat treatment was carried out at 1000°C in a precisely controlled gas flow of a CO–CO2 mixture (pCO/pCO2=10−1) at ambient pressure. This condition corresponds to an oxygen partial pressure of ~10−12 atm. The X-ray diffraction θ–2θ scanning and pole-figure analysis showed that the 0.5-μm-thick V2O3 films chiefly comprise the grains grown epitaxially to the substrate surfaces and a small amount of uniaxially oriented crystallites with the c-axis perpendicular to the substrate surfaces. In the films grown on the C- and A-planes of α-Al2O3, epitaxial grains grown 60°-rotated in the basal plane relative to the substrates (or 180° domains) were also present. The occurrence of the uniaxially c-axis-oriented and 180° domains may be attributed to the crystallization from the film surface accompanying the reduction of the precursors, which contain higher-valence vanadium ions, by the CO–CO2 mixed gas, whereas the epitaxial grains grow from the film/substrate interface.