Kunihito Koumoto

Room temperature deposition of a TiO2 thin film from aqueous peroxotitanate solution

A transparent, high purity, amorphous titanium dioxide thin film composed of densely packed nanometer-sized grains has been successfully deposited on a glass substrate at room temperature from an aqueous peroxotitanate solution using a simple, inexpensive, reproducible, and environmentally friendly method. The as-deposited thin film was 117 nm thick and composed of closely packed particles of 10–15 nm in diameter, but they aggregated into large grains of 50–100 nm in diameter. The aqueous peroxotitanate solution was obtained by dissolving metatitanic acid (H2TiO3) in a mixture of concentrated H2O2 and NH3·H2O. An anatase TiO2 thin film was obtained by heating the as-deposited thin film at 500 °C for 1 h in air. A chemical composition of TiO1.4(O2)0.5(OH)0.2·1.34H2O is proposed for the as-deposited thin film, based on XPS, FT-IR and TG-DTA data. Band gap energies of 3.20 eV for indirect transition and 3.63 eV for direct transition were obtained for the anatase TiO2 film.

Thermoelectric performance of Bi- and Na-substituted Ca3Co4O9 improved through ceramic texturing

Plate-like particles of Ca3Co4O9 have been prepared in which Bi and Na were partially substituted for Ca to improve the thermoelectric performance. Successfully fabricated dense and highly textured ceramics have been obtained by combining the templated grain growth technique (TGG) with hot-pressing (HP). Ca3Co4O9 single crystals, which have alternating layers of Co–O and Ca–Co–O in the direction of the c-axis, show high electrical conductivity along the layer compared with that across the layer. Hence, a highly oriented TGG + HP specimen showed high electrical conductivity compared with the specimen sintered under uniaxial pressure (UP + PLS). The improved electrical conductivity with high Seebeck coefficient of the highly oriented specimen (TGG + HP) gave a high thermoelectric power factor of 5.9 × 10−4 W m−1 K−2 at 1073 K. The figures-of-merit at 773 K and 1073 K were calculated to be 8.54 × 10−5 K−1 (ZT = 0.066 at 773 K) and 1.69 × 10−4 K−1 (ZT = 0.18 at 1073 K), respectively. These values are quite high among Ca–Co–O polycrystalline systems reported so far.

Selective deposition and micropatterning of titanium dioxide thin film on self-assembled monolayers☆

Ž. We succeeded in fabricating micropatterns of titanium dioxide thin films on SAMs self-assembled monolayers . SAMs of OTS Ž. octadecyltrichloro-silane were formed on Si wafers, and were modified by UV irradiation using a photomask to generate Ž methylsilanol-pattern. They were used as templates to deposit titanium dioxide thin films by the use of TDD titanium . dichloride diethoxide . Amorphous films with approximate compositions TiOClC 1:2.2:0.17:0.37 were selectively deposited on silanol regions. Line width variation of the pattern of an as-deposited film was improved to be well below the electronics Ž. design rule, 5%. Annealing the films at high temperatures 400600C gave rise to an anatase phase, while the resolution of a micropattern remained unchanged. 2001 Elsevier Science B.V. All rights reserved.

Enhanced thermoelectric performance of Nb-doped SrTiO3 by nano-inclusion with low thermal conductivity

Authors reported an effective path to increase the electrical conductivity while to decrease the thermal conductivity, and thus to enhance the ZT value by nano-inclusions. By this method, the ZT value of Nb-doped SrTiO3 was enhanced 9-fold by yttria stabilized zirconia (YSZ) nano-inclusions. YSZ inclusions, located inside grain and in triple junction, can reduce the thermal conductivity by effective interface phonon scattering, enhance the electrical conductivity by promoting the abnormal grain growth, and thus lead to the obvious enhancement of ZT value, which strongly suggests that, it is possible to not only reduce the thermal conductivity, but also increase the electrical conductivity by nano-inclusions with low thermal conductivity. This study will give some useful enlightenment to the preparation of high-performance oxide thermoelectric materials.

Thermoelectric Performance of Yttrium-substituted (ZnO)5In2O3 Improved through Ceramic Texturing

Thermoelectric oxides with comparatively high figures of merit possess layered structures. Because they exhibit thermoelectric anisotropy, textured crystal-axis-oriented ceramics should be produced in order to realize the best performance. We have succeeded in fabricating textured ceramics of yttrium-substituted (ZnO)5In2O3 by the reactive templated grain growth (RTGG) technique, and achieved the highest figure of merit (ZT~0.33 at 1073 K) among n-type oxide materials reported so far.

Nano/micro-patterning of anatase TiO2 thin film from an aqueous solution by site-selective elimination method

Abstract We proposed a novel method to fabricate nano/micro-scaled patterns of thin films and successfully fabricated patterns of anatase TiO2 thin films in an aqueous solution at 50 8C. The patterned self-assembled monolayer (SAM) having octadecyltrichlorosilane (OTS) regions and silanol regions was immersed in a solution containing a Ti precursor and subjected to ultrasonication for several hours. The difference in adhesion of thin films on substrates was employed for the site-selective elimination method. Heterogeneously nucleated TiO2 and homogeneously nucleated TiO2 particles adhering to the OTS–SAM could be easily eliminated from the substrate by ultrasonication, whereas those on silanol groups maintained their adhesion during the immersion period. TiO2 can form chemical bonds such as Ti–O–Si with silanol groups, but cannot form them with octadecyl groups, resulting in the difference in adhesion, which is the essence of the site-selectivity of this method. The site-selective elimination method can be applied to fabricate nano/micro-scaled patterns in the solution by the immersion of the substrate that has regions on which depositions adhere strongly and regions on which depositions adhere weakly, enabling elimination by treatment such as ultrasonication.

Seedless micropatterning of copper by electroless deposition on self-assembled monolayers

A novel approach for direct electroless (EL) patterning of copper films without catalysts has been developed. In a special electroless solution employed in the present study, the formation of copper particles was observed and the negatively charged surfaces were confirmed by zeta potential measurements. The conditions of the solution (ionic strength, pH, temperature, additives etc.) greatly affected the composition of the resulting precipitates. Results showed that pure copper films formed in EL solutions with pH higher than 7.3. A self-assembled monolayer (SAM) terminated with either NH2 or OH headgroups was employed as a template to enhance the selective adhesion of copper particles. As expected, many particles were deposited on the positive NH2-SAM by electrostatic attraction, while few particles were deposited on the negative OH-SAM due to repulsive interaction. The measurement results obtained by AFM, QCM, XRD and optical microscopy confirmed the selective formation of copper films on the NH2-SAM. Subsequently, micropatterns of copper films with high resolution were successfully produced. The deviation in the thickness of the deposit reached 110 nm between the NH2-SAM and OH-SAM after 90 min soaking in the EL solution. Current–voltage characteristics revealed relatively high resistivity (0.3 mΩ cm) of the formed copper film on the NH2-SAM, which can be ascribed to the poor connectivity among particles.

Arrangement of Nanosized Ceramic Particles on Self-Assembled Monolayers.

The fabrication of novel micro/nano-sized devices by assembling inorganic particles is anticipated for future microelectronics which will make use of their attractive functions. The surface modification of self-assembled monolayers (SAMs) was studied to prepare templates for sphere assembly. Phenyl groups of SAM were modified into silanol groups by UV irradiation through a photomask, by applying an electric current using an atomic force microscope (AFM) probe, or by contact pressure with a diamond tip. They were used as templates to arrange fine inorganic particles. In addition to the formation of ester bonds, siloxane bond formation between spheres and SAMs was also found to be effective for sphere arrangement. Low-dimensional close-packing of SiO2 spheres was achieved through the formation of siloxane bonds. The two-dimensional arrangement of functional particles on SAMs in a controlled manner through the formation of strong chemical bonds, such as ester bonds or siloxane bonds, can be applied to the microfabrication of ceramic devices.

Dielectric Mismatch Mediates Carrier Mobility in Organic-Intercalated Layered TiS2.

The dielectric constant is a key parameter that determines both optical and electronic properties of materials. It is desirable to tune electronic properties though dielectric engineering approach. Here, we present a systematic approach to tune carrier mobilities of hybrid inorganic/organic materials where layered two-dimensional transition-metal dichalcogenide TiS2 is electrochemically intercalated with polar organic molecules. By manipulating the dielectric mismatch using polar organic molecules with different dielectric constants, ranging from 10 to 41, the electron mobility of the TiS2 layers was changed three times due to the dielectric screening of the Coulomb-impurity scattering processes. Both the overall thermal conductivity and the lattice thermal conductivity were also found to decrease with an increasing dielectric mismatch. The enhanced electrical mobility along with the decreased thermal conductivity together gave rise to a significantly improved thermoelectric figure of merit of the hybrid inorganic/organic materials at room temperature, which might find applications in wearable electronics.

Preparation of SrTiO3 thin films by the liquid phase deposition method

Successful preparation of strontium titanate (SrTiO3; STO) thin films has been realized by the liquid phase deposition method. The STO precursor solid thin films with close-packed grains smaller than 200 nm were fabricated from an aqueous solution of Sr(NO3)2/(NH4) 2 TiF6/H3BO3/1/1/3 (molar ratio) at 50 8C on a Si substrate. X-ray photoelectron spectroscopy analysis showed that the as-deposited film contained fluorine as an impurity, which could be completely eliminated by annealing at 500 8C in air, accompanying the crystallization of the as-deposited amorphous thin film into perovskite-type STO. # 2002 Elsevier Science B.V. All rights reserved.