Yoshifumi Aoi

Photocatalytic activity of titanium oxide prepared by liquid phase deposition (LPD)

Titanium oxide powder and thin films were prepared from an (NH4)2TiF6 aqueous solution upon addition of boric acid in a process denoted as liquid phase deposition (LPD). In this process, titanium oxide powder and films were formed by the chemical equilibrium reaction between titanium fluoro-complex ions and metal oxide in the aqueous solution. The prepared powder and deposited films showed some features which differed from titanium oxide prepared from titanium alkoxide. The prepared powder and the deposited films included anatase (TiO2) and showed photocatalytic activity without prior calcination. The decomposition rate of CH3CHO reached a maximum when the powder or films were calcined at 300 °C. The LPD process enabled a uniform layer of TiO2 film to form homogeneously on the entire surface of glass wool. The prepared TiO2 contained fluorine and nitrogen. The amount of these impurities was reduced upon calcination.

Preparation of amorphous CNx thin films by pulsed laser deposition using a radio frequency radical beam source

Amorphous CNx thin films were deposited by pulsed laser deposition (PLD) combined with a nitrogen rf radical beam source which supplies active nitrogen species to the growing film surface. The dominant active nitrogen species are excited N2 molecules and nitrogen atoms. The deposited films were characterized by scanning electron microscope, x-ray photoelectron spectroscopy (XPS), Raman scattering, and Fourier transform infrared (FTIR) spectroscopy. Nitrogen content of the deposited films increased with increasing rf input power and N2 pressure in the PLD chamber. The N/C ratio 0.23 was obtained at 400 W of rf input power and 1.3 Pa. XPS N 1s spectra shows the existence of N–sp2C and N–sp3C bonds in the deposited films. The fraction of the N–sp3C increased with increasing of N2 pressure in the PLD chamber during the operation of radical beam source. FTIR and Raman spectra of the deposited films indicated that N≡C bonds in the films were few as compared to the other carbon and nitrogen bonds.

Preparation and characterization of iron oxyhydroxide and iron oxide thin films by liquid-phase deposition

Iron oxyhydroxide thin films have been prepared from the aqueous solution system of FeOOH–NH 4 F·HF (aq.) with added boric acid by a novel liquid-phase deposition (LPD) method and is the first attempt to preparate iron oxide thin films by this method. A crystalline β-FeOOH thin film was formed directly on the substrate upon immersion into a mixed solution of FeOOH–NH 4 F·HF and H 3 BO 3 . The orientation of the deposited film differed according to the concentration of H 3 BO 3 in the solution. When the concentration of H 3 BO 3 was >0.30 mol dm -3 , the β-FeOOH thin film was preferentially oriented in the [211] direction. The β-FeOOH thin film formed was transformed into α-Fe 2 O 3 upon heat treatment in air flow. The α-Fe 2 O 3 thin films obtained were oriented in the [110] direction. The F content of the as-deposited β-FeOOH film was ca. 15% F/Fe and was reduced to 0.19% upon heat treatment.

Preparation and characterization of Au-dispersed TiO2 thin films by a liquid-phase deposition method

Au-dispersed TiO2(anatase) thin films have been prepared by a novel method, liquid-phase deposition (LPD). The deposited films were characterized by XRD, XPS, TEM and UV–VIS absorption spectroscopy. The results showed that the titanium oxide thin film containing AuIII ions was formed from a mixed solution of ammonium hexafluorotitanate, boric acid and tetrachloroauric acid. Heat treatment above 200 °C of the deposited film under flowing air produced dispersed Au metal particles, accompanied by the crystallization of titanium oxide as a matrix. The mean particle size of the dispersed Au particles was ca. 15 nm. The optical absorption band due to the surface plasmon resonance of the dispersed Au particles shifted toward longer wavelengths with increasing heat-treatment temperature.

A novel wet process for the preparation of vanadium dioxide thin film

Thin films of vanadium oxide have been prepared from an aqueous solution system of (V2O5–HF aq.) with the addition of aluminium metal by a novel wet-preparation process which is called liquid-phase deposition (LPD). From X-ray diffraction measurements, the as-deposited film was found to be amorphous and it was then crystallized to V2O5 by calcination at 400 °C under an air flow. In contrast, the monoclinic VO2 phase was obtained when the deposited film was calcined under a nitrogen atmosphere. The deposited film showed excellent adherence to the substrate and was characterized by a homogeneous flat surface. The deposited VO2 film exhibited a reversible semiconductor–metal phase transition around 70 °C and its transition behaviour depended on the way in which the film was prepared.

Synthesis of metal oxide thin films by liquid-phase deposition method

A novel wet process to synthesize metal oxide thin films has been developed. The process is called the Liquid-Phase Deposition (LPD) method. In this method, metal oxide or hydroxide thin films are formed on the substrate through the ligand-exchanging (hydrolysis) equilibrium reaction of metal-fluoro complex species and the F − consumption reaction of a F − scavenger. The LPD method is a unique soft solution process, and is performed by very simple procedures. In this paper, we develop a method of preparing composite oxide thin films, Pt-dispersed titanium oxide, and iron-nickel binary oxide thin films.

Monitoring the growth of titanium oxide thin films by the liquid-phase deposition method with a quartz crystal microbalance

The quartz crystal microbalance (QCM) technique has been applied to investigate the formation of titanium oxide thin films by the liquid-phase deposition (LPD) method. A linear relationship was observed between the thickness measured by the QCM technique and that measured by direct observation with a scanning electron microscope, indicating that it is possible to monitor the growth of thin films from aqueous solution systems by the LPD method with the QCM technique. The concentration effects of free F - , H 3 BO 3 and (NH 4 ) 2 TiF 6 on the film deposition rate are discussed.

COMPOSITION AND CRYSTAL STRUCTURE OF CARBON NITRIDE FILMS PREPARED BY THE ELECTRON CYCLOTRON RESONANCE PLASMA SPUTTERING METHOD

Carbon nitride films were prepared on a Si(100) substrate by an electron cyclotron resonance plasma sputtering method using a carbon target and a nitrogen atmosphere. The maximum value of the N/C ratio in the film deposited at a substrate bias potential of about −55 V and ambient temperature was 1.35, which is close to the stoichiometric composition of C3N4. The surface morphology observed with scanning electron microscopy of the film deposited at 600 °C showed a crystalline structure with a 500 nm average grain diameter. The x-ray diffraction pattern of the film deposited at 600 °C and a substrate bias potential of −50 V indicates no amorphous phase in the film, which is composed of β- and α-C3N4 phases containing an unidentified C–N phase.

Effects of heat treatment on structure of amorphous CNx thin films by pulsed laser deposition

Abstract Investigation of compositional and structural modifications induced by heat treatment of pulsed laser deposited amorphous CN x ( x ∼0.23) thin film has been carried out. Fourier transform infrared, Raman scattering, X-ray photoelectron spectroscopies were carried out to investigate compositional and structural properties of films. The heat treatment induces a nitrogen loss of the film. The N/C ratio decreased from 0.23 for the as-deposited film to 0.17 for the film heat treated at 800°C. N1s electron spectra showed nitrogen atoms bonded to sp 3 hybridized carbon preferentially removed by heat treatment, although those bonded to sp 2 hybridized carbon were stable. Simultaneously, growth of graphitic domains, i.e. graphitization of the film by heat treatment was observed by Raman spectroscopy. The nitrogen loss and changes in bonding structure concerned with nitrogen atoms by heat treatment are caused by the graphitization of amorphous CN x film induced by heat treatment.

Synthesis of mesoscopic hollow spheres and inner surface functionalized hollow spheres of titanium dioxide by the liquid phase deposition method

Polystyrene (PS) core–TiO 2 shell composite particles and TiO 2 hollow spheres were fabricated using the liquid phase deposition (LPD) method. Composite particles were prepared using PS particles as templates. Calcination of the composite particles resulted in TiO 2 hollow spheres. Uniform TiO 2 hollow spheres were obtained when the reaction time of the LPD process was between 4 and 8 h. Furthermore, we fabricated TiO 2 hollow spheres whose inner surfaces were functionalized by Pt particles after platinized PS particles were used as templates. The Pt particles were immobilized on the inner surfaces of the hollow spheres.