Noboru Tohge

PREPARATION OF ZnS NANOPARTICLES BY ELECTROSPRAY PYROLYSIS

Zinc sulfide particles 20–40 nm in diameter were prepared by electrically driven spray pyrolysis. Solutions of ethyl alcohol with zinc nitrate (Zn(NO3)2) and thiourea (SC(NH2)2) at concentrations from 0.0025 to 0.2 mol l-1 and electrical conductivities between 10-4 and 10-1 S m-1 were electrosprayed from steady cone-jets at flow rates from 0.05 to 0.25 ml h-1, with positive and negative polarity. The initially highly charged drops formed were neutralized by bipolar ions from a radioactive source to increase the overall transmission efficiency through a reactor furnace. This process was made particularly effective by the innovation of placing the ion source directly within the electrospray chamber. The diameters of the final ZnS particles were measured on-line by a differential mobility analyzer and a condensation nucleus counter. In spite of ambiguities in the flow rate of liquid through the cone–jet (associated to solvent evaporation from the meniscus), these diameters agree approximately with values expected from available scaling laws. Transmission electron micrographs also confirmed these results. Electrospray pyrolysis is hence able to generate non-agglomerated and spherical ZnS nanoparticles with geometrical standard deviation σg of about 1.3.

Effects of UV-irradiation on the formation of oxide thin films from chemically modified metal-alkoxides: Code: EP22

The effects of UV-irradiation on the properties of ZrO2 and TiO2 gel films prepared from corresponding metal-butoxides modified with acetylacetone (AcAc) or benzoylacetone (BzAc) have been studied. It was found that the chelate bonds of β-diketones remaining in the gel films were dissociated by the UV-irradiation. The UV-irradiation also changed the properties of the gel films such as solubility; the solubility in acidic solutions was decreased for ZrO2 gel films modified with AcAc and TiO2 gel films modified with BzAc became insoluble in alcohol. Based on these findings, a new fine-patterning process has been established, which enables us to make fine-patterns of ZrO2 and TiO2 films on a variety of substrates.

Photosensitive gel films prepared by the chemical modification and their application to surface-relief gratings

Abstract A novel technique has been developed to fabricate surface-relief gratings using photosensitive gel films. Gel films which were derived from metal-alkoxides chemically modified with β -diketones were photosensitive owing to remaining chelate rings; the UV-irradiation of these gel films substantially decreased their solubility in acidic aqueous solutions or organic solvents. Leaching of the gel films after UV-irradiation through a mask and subsequent heat-treatment gave negative patterns of the mask used. Fine-patterns of PLZT films, as well as Al 2 O 3 , ZrO 2 , and TiO 2 films, were successfully formed by the above process. Utilizing this process, surface-relief gratings were fabricated on silica glass and Si substrates by the irradiation of the modified gel films with a XeF excimer laser through a phase mask. Very uniform diffraction gratings with a pitch of about 1.0 μm were produced for Al 2 O 3 , ZrO 2 , and TiO 2 films, along with PLZT films. The morphology and diffraction efficiency of the gratings obtained were examined in terms of fabrication conditions.

Patterning Effect of a Sol-Gel TiO2 Overlayer on the Photocatalytic Activity of a TiO2/SnO2 Bilayer-Type Photocatalyst

TiO2 films with a thickness of 75 ± 5 nm (anatase) were formed on SnO2-film (580 ± 80 nm) coated soda-lime glass substrates (SnO2/SL-glass) by a sol-gel method. Although the photocatalytic activity for CH3CHO oxidation (λex > 300 nm) significantly exceeded that of a standard TiO2/quartz sample, it decayed with illumination time (t) at t > 0.75 h. Stripes of anatase TiO2 films of 40 nm in thickness and 1 mm in width were prepared on the SnO2/SL-glass substrate in a 1-mm pitch by photolysis of an organically modified sol-gel film. The TiO2 patterning further increased the photocatalytic activity by a factor of 4.1 as compared to the non-patterned sample, and it was also maintained at 0 < t < 2 h. The flat band potentials of the TiO2 and SnO2 films are determined to be −0.34 and +0.07 V (vs. SHE), respectively, at pH = 7 by the Mott-Schottky plots. On the basis of the results, the outstanding patterning effects could be rationalized in terms of the vectorial charge separation at the interface between TiO2 and SnO2.

Coating and water permeation properties of SiO2 thin films prepared by the sol-gel method on nylon-6 substrates

Nylon-6 substrates were coated with SiO2 thin films by the sol-gel method and their water permeability coefficient was evaluated. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were used as starting materials. The addition of MTES to TEOS has enabled the formation of crack-free thin films on the substrates. The thin films strongly adhered to the substrates. The water permeability coefficients of nylon-6 substrates coated with these thin films decreased with the increase in the ratio of TEOS to the total alkoxides. The pretreatment of the nylon-6 substrates with γ-aminopropyltriethoxysilane was found to be effective to suppress the water permeability. The water permeability was suppressed by about 40% under the optimal condition.

Fine-Patterning of ZrO2 Thin Films by the Photolysis of Chemically Modified Gel Films

The effects of UV irradiation on the properties of gel films prepared from Zr- n-butoxides modified with acetylacetone (AcAc) have been studied. The irradiation with UV light corresponding to the π-π* transition in the chelate ring of AcAc was found to dissociate the chelate bonds in the gel films and simultaneously decrease the solubility of these gel films in acidic solutions. This finding was applied to the patterning of ZrO2 thin films; a gel film was irradiated through a mask, leached in an acidic solution, and heat-treated. Through the process above, finely patterned ZrO2 films were fabricated on various substrates.

Preparation of photosensitive gel films and fine patterning of amorphous Al2O3-SiO2 thin films

The effects of UV irradiation on the properties of xAl{sub 2}O{sub 3} {center_dot} (100 {minus} x)SiO{sub 2} gel films, which were obtained from aluminum butoxide chemically modified with benzoylacetone and partly hydrolyzed silicon ethoxide, have been studied. These gel films showed an optical absorption band at around 325 nm characteristic of the {pi}-{pi}* transition in chelate rings of {beta}-diketonate ligands. The irradiation of the gel films with UV light of 365 nm dissociated the chelate ring and simultaneously decreased the solubility of the gel films in ethanol containing HNO{sub 3}. This finding was successfully applied to the fine patterning of xAl{sub 2}O{sub 3} {center_dot} (100 {minus} x)SiO{sub 2} gel films with x = 30 or above. The gel films were leached in ethanol containing HNO{sub 3}, after UV irradiation through a mask, and heat-treated at 400 C for 20 min to give patterned amorphous Al{sub 2}O{sub 3}-SiO{sub 2} films.

Diffraction gratings of photosensitive ZrO 2 gel films fabricated with the two-ultraviolet-beam interference method

Photosensitive ZrO(2) gel films were patterned with a two-beam interference method by use of a 325-nm-wavelength He-Cd laser for the first time to our knowledge. The ZrO(2) gel films were prepared from Zr(O-n-C(4)H(9))(4) chemically modified with benzoylacetone. We fabricated uniform gratings with a 0.5-microm period on Si or SiO(2) substrates by etching the gel films in ethyl alcohol after UV irradiation. A maximum diffraction efficiency of 28% was attained with the grating fabricated on Si substrate under a Littrow mounting condition by use of a 633-nm-wavelength He-Ne laser. Blazed gratings could also be fabricated.

Particle generation and film formation in an atmospheric-pressure chemical vapour deposition process using tetraethylorthosilicate

Effects of an oxygen flow rate on film formation and nanometre-sized particle generation in the gas phase were examined simultaneously in an atmospheric-pressure chemical vapour deposition reactor using tetraethylorthosilicate (TEOS). The critical temperature for particle generation decreased rapidly to 340‡C from 740‡C with increasing oxygen flow rate, but it decreased slightly to 600‡C from 700‡C for film formation. There were no conditions where film was deposited without particle generation in a TEOS/O2 system. The nanometre-sized particles generated in the systems were amorphous and non-spherical, and their size distributions were polydisperse. The Fourier transform infrared (FT-IR) and thermal desorption (TDS) spectra of the particles were not affected by oxygen flow rate, and showed that the particles contained a small amount of an ethoxy group and a relatively large amount of a hydroxyl group. It was found from comparisons between FT-IR and TDS spectra of particles and films that the SiO2 films were formed by Β-elimination reactions, where C2H4 and H2O are released from the ethoxy group.

Characteristics of Diffraction Gratings Fabricated by the Two-Beam Interference Method Using Photosensitive Hybrid Gel Films

Diffraction gratings of arbitrary periods have been fabricated by the two-beam interference method using photosensitive ZrO2 gel films and characterized. The ZrO2 gel films were formed on Si or silica glass substrates from sols that were derived from Zr-butoxide modified chemically with benzoylacetone. The gel films were irradiated with two interference beams from a He-Cd laser (325 nm) and then leached in ethyl alcohol. The above process gave uniform surface-relief gratings of periods ranging from 1.0 to 0.5 μm, depending on the incidence angle of the interference beams. The diffraction efficiency, measured in the Littrow configuration using a He-Ne laser (633 nm), showed polarization dependence for the grating of 0.5 μm period but not for the gratings of 1.0 μm period. The maximum diffraction efficiency was 18% for the grating of 1.0 μm period and 28% for that of 0.5 μm period in the reflection mode. The present study has proved that the photosensitive gel films are versatile in fabrication of optical devices.