Woo-Seok Cho

Room‐temperature preparation of the highly crystallized luminescent CaWO4 film by an electrochemical method

Highly crystallized polycrystalline film of single‐phase CaWO4 has been prepared on a tungsten substrate at room temperature in an alkaline solution containing calcium ions by an electrochemical method with the current density of 1 mA/cm2. This film showed blue emission (456 nm wavelength) with excitation light (254 nm wavelength) at room temperature.

Synthesis of carbon nanotubes from bulk polymer

Carbon nanotubes have been synthesized by heat treating the polymer at 400 °C in air which was obtained by polyesterification between citric acid and ethylene glycol. Transmission electron micrographs and an electron diffraction pattern showed the formation of carbon nanotubes. The diameter of the tubes ranged from 5 to 20 nm, whereas the lengths were less than 1 μm.

Room‐temperature preparation of crystallized luminescent Sr1−xCaxWO4 solid‐solution films by an electrochemical method

A complete series of well‐crystallized solid‐solution oxide films, Sr1−XCaXWO4 (0≤X≤1), has been prepared on a tungsten substrate in the electrolytic solution containing Sr2+ and Ca2+ ions by an electrochemical method at room temperature (25 °C). The composition of solid‐solution oxide films could easily be controlled by the concentrations of Sr and Ca species in the starting solutions. The films showed only single blue emission at liquid nitrogen temperature (−196 °C), strongly suggesting that they consisted of well‐crystallized defect‐free crystals.

Preparation of highly crystallized BaMoO4 film using a solution reaction assisted by electrochemical dissolution of molybdenum

Abstract Highly crystallized BaMoO 4 films have been prepared on a molybdenum substrate in an alkaline solution containing barium ions at room temperature (25 °C). The film formation is based on a solution reaction assisted by an electrochemical dissolution of metal molybdenum. The film (thickness ~ 3 μm) was polycrystalline with a grain size of about 6 μm. The film morphology is related to the nucleation and growth behavior of the BaMoO 4 particles on a molybdenum metal substrate.

Direct fabrication of crystalline vanadates films by hydrothermal-electrochemical method

Abstract Lithium vanadate films have been prepared on vanadium metal substrates using lithium hydroxide aqueous solutions in the autoclave by the hydrothermal-electrochemical method. The X-ray diffraction pattern of the fabricated film showed a single phase of stoichiometric crystalline orthorhombic βII-Li3VO4 without any other impurity phases. As an application of this method, we have demonstrated the direct fabrication of europium doped YVO4 films on vanadium substrate for luminescent materials using hydrothermal-electrochemical method. Those films showed sufficient intensity of luminescent property at room temperature. Therefore, this processing route may serve as an inexpensive and environmentally friendly way of the direct fabrication of the vanadate films with controlled crystal morphology and size simply by changing synthesis parameters.

Stacking faults in BaTiO3 particles synthesized from organic precursor

BaTiO3 powder has been synthesized by heat treating (BaTi) citrate polyester resins at 500 °C for 8 h. X-ray powder diffractometry (XRD) and Raman spectroscopy data suggest the presence of a high-temperature hexagonal phase at room temperature. However, high-resolution transmission electron microscopy indicates that the peaks that were ascribed to the above phase in the Raman and XRD spectra may originate from stacking faults in the particles. Our results disprove the existence of the high-temperature hexagonal BaTiO3 at room temperature.

Structural evolution and characterization of crystallized luminescent Sr1−xCaxWO4 solid-solution films prepared by an electrochemical method at room temperature

A complete series of well-crystallized solid-solution oxide films, Sr1−XCaXWO4 (0⩽X⩽1), has been prepared on a tungsten substrate in an electrolytic solution containing Sr2+ and Ca2+ ions by electrochemical anodization of tungsten substrates at room temperature (25 °C). The composition of the solid-solution oxide films was investigated using Vergard’s law and x-ray photoelectron spectroscopy. The peak positions of excitation and emission of the films were independent of the Ca content. However, there were variations in the intensities of the emissions: the Ca-rich films showed an extremely strong luminescence, while the Sr-rich films showed a much fainter emission. The crystallization of the films was apparently characterized by three-dimensional nucleation and growth. A model is proposed for the mechanism for formation and growth of the films.

Preparation of Crystallized Ba-Rich Ba1-XCaXWO4 Solid-Solution Films by an Electrochemical Method at Room Temperature and Their Luminescence

Well crystallized solid-solution Ba1-X CaX WO4 films have been prepared on tungsten substrates in an electrolytic solution containing Ba2+ and Ca2+ ions by an electrochemical method at room temperature (25° C). CaWO4 film showed only blue emission at liquid nitrogen temperature (-196° C), strongly suggesting that it consisted of well crystallized defect-free crystals. However, the other films did not luminesce at this temperature.