• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.1-7
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• 2017

Polydimethylsiloxane (PDMS) can be deposited on various substrates using chemical vapor deposition process, which results in the formation of PDMS thin films with thickness below 5 nm. PDMS layers can be evenly deposited on surfaces of nanoparticles composed of various chemical compositions such as $SiO_2$, $TiO_2$, ZnO, C, Ni, and NiO, and the PDMS-coated surface becomes completely hydrophobic. These hydrophobic layers are highly resistant towards degradation under acidic and basic environments and UV-exposures. Nanoparticles coated with PDMS can be used in various environmental applications: hydrophobic silica nanoparticles can selectively interact with oil from oil/water mixture, suppressing fast diffusion of spill-oil on water and allowing more facile physical separation of spill-oil from the water. Upon heat-treatments of PDMS-coated $TiO_2$ under vacuum conditions, $TiO_2$ surface becomes completely hydrophilic, accompanying formation oxygen vacancies responsible for visible-light absorption. The post-annealed $PDMS-TiO_2$ shows enhanced photocatalytic activity with respect to the bare $TiO_2$ for decomposition of organic dyes in water under visible light illumination. We show that the simple PDMS-coating process presented here can be useful in a variety of field of environmental science and technology.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.189-199
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• 2009

The Powder characteristics and sintering behavior of $SiO_2$ coated $BaTiO_3$ were studied. $BaTiO_3$ powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the $BaTiO_3$ powders was 35 nm and the thickness of the $SiO_2$ coating layer was 5 nm. As the $SiO_2$ content increased, the $SiO_2$ layers improved the powder dispersion by increasing electrostatic repulsion between the $BaTiO_3$ particles. Effects of MgO coating on microstructure and dielectric properties of $BaTiO_3$ have been studied compared with mechanically MgO mixed $BaTiO_3$. MgO coated $BaTiO_3$ particles were prepared by a homogeneous precipitation method using $MgCl_2\cdot 6H_2O$ and urea. MgO coated $BaTiO_3$ exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. Electrical properties of MgO mixed and coated $BaTiO_3$ were affected by the diffusion behavior of Mg in $BaTiO_3$ lattice.

• Journal of Powder Materials
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• v.25 no.1
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• pp.1-6
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• 2018

Uniform $TiO_2$ blocking layers (BLs) are fabricated using ultrasonic spray pyrolysis deposition (USPD) method. To improve the photovoltaic performance of dye-sensitized solar cells (DSSCs), the BL thickness is controlled by using USPD times of 0, 20, 60, and 100 min, creating $TiO_2$ BLs of 0, 40, 70, and 100 nm, respectively, in average thickness on fluorine-doped tin oxide (FTO) glass. Compared to the other samples, the DSSC containing the uniform $TiO_2$ BL of 70 nm in thickness shows a superior power conversion efficiency of $7.58{\pm}0.20%$ because of the suppression of electron recombination by the effect of the optimized thickness. The performance improvement is mainly attributed to the increased open-circuit voltage ($0.77{\pm}0.02V$) achieved by the increased Fermi energy levels of the working electrodes and the improved short-circuit current density ($15.67{\pm}0.43mA/cm^2$) by efficient electron transfer pathways. Therefore, optimized $TiO_2$ BLs fabricated by USPD may allow performance improvements in DSSCs.

• Journal of the Korean institute of surface engineering
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• v.36 no.1
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• pp.14-21
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• 2003

Thin films of ZrO$_2$ and TiO$_2$ were deposited on Si(100) substrates using RF magnetron sputtering technique. To study an influence of the sputtering parameters, systematic experiments were carried out in this work. XRD data show that the $ZrO_2$ films were mainly grown in the [111] orientation at the annealing temperature between 800 and $1000^{\circ}C$ while the crystal growth direction was changed to be [012] at above $1000^{\circ}C$. FT-IR spectra show that the oxygen stretching peaks become strong due to $SiO_2$ layer formation between film layers and silicon surface after annealing, and proved that a diffusion caused by either oxygen atoms of $ZrO_2$ layers or air into the interface during annealing. Different crystal growth directions were observed with the various deposition parameters such as annealing temperature, RF power magnitude, and added $O_2$ amounts. The growth rate of $TiO_2$ thin films was increased with RF power magnitude up to 150 watt, and was then decreased due to a sputtering effect. The maximum growth rate observed at 150 watt was 1500 nm/hr. Highly oriented, crack-free, stoichiometric polycrystalline $TiO_2$<110> thin film with Rutile phase was obtained after annealing at $1000^{\circ}C$ for 1 hour.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.1
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• pp.23-29
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• 2007

Pitch-coated anatase $TiO_2$ typed was prepared by $CCl_4$ solvent mixing method with different mixing ratios. Since the carbon layers derived from pitch on the $TiO_2$ particles were porous, the pitch-coated $TiO_2$ sample series showed a good adsorptivity and photo decomposition activity. The BET surface area for the carbon layer in the sample increases to increasing with pitch contents. The SEM results present to the characterization of porous texture on the pitch-coated $TiO_2$ sample and pitch distributions on the surfaces for all the materials used. From XRD data a weak and broad carbon peak of graphene with pristine anatase peaks were observed in the X-ray diffraction patterns for the pitch-coated $TiO_2$. The EDX spectra show the presence of C, O and S with strong Ti peaks. Most of these samples are richer in carbon and major Ti metal than any other elements. Finally, the excellent photocatalytic activity of pitch-coated $TiO_2$ with slope relationship between relative concentration of MB ($c/c_o$) and t could be attributed to the homogeneous coated pitch on the external surface by $CCl_4$ solvent method.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.688-693
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• 2008

This paper presents a study on the photocatalytic reaction about the composite particles of $TiO_2$-coated phosphors under visible light irradiation. Nanocrystalline titanium dioxide layers were directly coated on the alkaline earth aluminate phosphor, $CaAl_2O_4:Eu^{2+},\;Nd^{3+}$ particles by an sol-gel processing method. The photocatalytic reaction was analyzed with the degradation of methylene blue (MB) aqueous solution under UV and visible light irradiations. $TiO_2$-coated phosphor powders showed different photocatalytic mechanism, compared with pure $TiO_2$ (P-25, Degussa). Under UV-irradiation, $TiO_2$-coated phosphor powders showed slow photocatalytic reactivity in the early stage and fast in the latter, compared with that of pure $TiO_2$. However, $TiO_2$-coated phosphor powders showed much faster photocatalytic reactivity than that of pure $TiO_2$ under visible irradiation. In addition, the characterizations of the $TiO_2$-coated phosphor powders were conducted by a X-ray diffractometer (XRD), transmission electron microscope (TEM), and energy dispersive spectroscopy (EDS).

• Korean Journal of Crystallography
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• v.13 no.2
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• pp.57-62
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• 2002

Time-of-flight impact-collision ion scattering spectroscopy (TOF-ICISS) was applied to study the geometrical structure of epitaxially grown TiO layers on a MgO(001) surface. The hetero-epitaxial TiO layer was deposited by thermal evaporation of titanium onto the MgO(001) surface and subsequent exposure to oxygen at 400℃. The well-ordered TiO structure was confirmed with the 1×1 RHEED pattern. TOF-ICISS results revealed that the TiO layer was formed at the on-top sites of the MgO(001) substrate and that the lateral lattice constant of TiO layer was the same as that of the MgO substrate. The surface of the deposited epitaxial TiO layer was smooth without the three dimensional islands.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.3043-3047
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• 2012

To investigate the scattering layer effect of a $TiO_2$ multilayer in dye-sensitized solar cells (DSSCs), we designed a new DSSC system, assembled with a CdS-$TiO_2$ scattering layer electrode. A high-magnification SEM image exhibited hollyhock-like particles with a width of 1.5-2.0 ${\mu}m$ that were aggregated into 10-nm clumps in a hexagonal petal shape. The efficiency was higher in the DSSC assembled with a CdS-$TiO_2$ scattering layer than in the DSSC assembled with $TiO_2$-only layers, due to the decreased resistance in electrochemical impedance spectroscopy (EIS). The short-circuit current density ($J_{sc}$) was increased by approximately 7.26% and the open-circuit voltage ($V_{oc}$) by 2.44% over the 1.0 wt % CdS-$TiO_2$ composite scattering layer and the incident photon-to-current conversion efficiency (IPCE) in the maximum peak was also enhanced by about 5.0%, compared to the DSSC assembled without the CdS-$TiO_2$scattering layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.366.2-366.2
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• 2014

Impedance spectroscopy allows for simultaneous characterization of interface-controlled materials and/or devices in terms of electrical and dielectric aspects. Recently, there have tremendous interests in 2-dimensional electron gas layers (2DEGs) involving $LaAlO_3$ and $SrTiO_3$ whose features incorporates extremely high mobility and carrier concentrations along with metallic responses unlike the constituents, $LaAlO_3$ and $SrTiO_3$. Impedance spectroscopy offers the following unique features, such as simultaneous determination of conductivity and dielectric constants, identification of electrical origins among bulk-, grain boundary-, and electrode-based responses. Impedance spectroscopy was applied to the 2DEG $LaAlO_3/SrTiO_3$ system, in order to extract the electrical and dielectric information operating in the 2DEG system. The unique responses of the 2DEG system are investigated in terms of temperature and device structures. The underlying mechanism of the 2DEG system is proposed with the aim to optimizing the high-mobility 2DEG responses and to expedite the associated devices towards the high-density integrated chips.

• Korean Chemical Engineering Research
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• v.45 no.4
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• pp.378-383
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• 2007

A novel fabrication method for the multi-component metal oxides such as zirconium titanate($Zr_xTi_{1-x}O_2$) has been suggested, which would yield the uniform film characteristics and control the film composition at relatively low process temperature. The method has the basic concept that firstly layer-by-layer structure is constructed with the primitive oxide layers, which are components of the desired multi-component oxides, and secondly the film is annealed at appropriate thermal conditions for the transformation to a single-phase multi-component oxides. In this study, PRTMOCVD(pulsed rapid thermal metalorganic chemical vapor deposition) possessing the superior thickness controllability was introduced to prepare $ZrO_2$ and $TiO_2$ thin film for zirconium titanate. Single-phase zirconium titanate thin films have been prepared successfully by the interdiffusion of oxide multilayers having several alternating layers of $ZrO_2$ and $TiO_2$. The Zr/Ti ratio of zirconium titanate could be controlled easily by altering the thickness of $ZrO_2$ and $TiO_2$ thin film.