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ABSTRACT: Al + SiC, Al + Al2O3 composites as well as pure Al, SiC, and Al2O3 coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition
of metal (Al) and ceramic (SiC, Al2O3) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was
fixed at 0.7 MPa. SiC and Al2O3 have been successfully sprayed producing coatings with more than 50 µm in thickness with the incorporation of Al as a binder.
Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was
no crater formation on hard Si substrates. However, when Al mixed with SiC and Al2O3, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.
Journal of Thermal Spray Technology 04/2012; 13(2):184-189. · 1.81 Impact Factor
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ABSTRACT: Dense and adhesive WO3 films were prepared on a silicon substrate by the cold gas dynamic spray process (or cold spray). In contrast to standard
metallic coatings, there was no sizable crater formation and plastic deformation. However, the aggregation of raw powder particles
of a relatively large size was found to be destroyed upon impact on the substrate, forming a highly irregular surface with
very fine secondary particles and providing good interlocking powder and void reduction among the particles in the coating.
High-resolution images of the substrate interface showed that particles at the interface were more densely packed and that
good adhesion was obtained. There fore, the particle bombardment onto the first layer of the coating could provide enhanced
adhesion to the substrate mechanically and/or chemically.
Journal of Thermal Spray Technology 04/2012; 14(2):183-186. · 1.81 Impact Factor
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ABSTRACT: Using a lead zinc niobate (PZN) thin film dielectric, a tunable metal-insulator-metal (MIM) capacitor is presented and investigated in this article. To improve its tunability and bias characteristics, the finger patterned electrode in the top metal is devised. The capacitors were fabricated on a low-resistivity Si substrate employing lead zinc niobate (PZN) thin film dielectric. The fabricated capacitor, whose line width and spacing was 2.5 and 2.0 μm, respectively, achieved the effective capacitance tunability of 22.9% at 5.5 V. This achieved tunability is higher value of 10% than that of the conventional rectangular MIM capacitor at 900 MHz. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 418–421, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24108
Microwave and Optical Technology Letters 01/2009; 51(2):418 - 421. · 0.62 Impact Factor
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ABSTRACT: In this work, we present tunable inter-digital capacitors (IDC's) employing high tunable PbO-ZnO-Nb<sub>2</sub>O<sub>5</sub> (PZN) cubic pyrochlore thin film dielectrics for low-voltage and high-tunability microwave applications. In order to reduce the bias voltage of the IDC and increase its tunability, its electrodes were fully embedded into the thin film dielectrics to confine fringing electric fields within them. In 4 V, the tunability of the IDCs was analyzed in terms of the electrode width and spacing by measuring reflection coefficients at 1 GHz. The fabricated IDC with width and spacing of 1.5 and 1.8 mum, respectively, achieved tunability of 26 % and Q-factor of 10 at the applied DC voltage of 5.5 V.
Microwave Integrated Circuit Conference, 2007. EuMIC 2007. European; 11/2007
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ABSTRACT: Employing high-tunability PbO–ZnO–Nb2O5 thin film dielectrics, low-voltage and high-tunability interdigital capacitors (IDCs) were implemented on a silicon substrate. In order to reduce the bias voltage of the IDC and increase its tunability, its electrodes were fully embedded into the thin film dielectrics to confine fringing electric fields within them. At 4 V, the tunability of the IDCs was analyzed in terms of the electrode width and spacing by measuring reflection coefficients at 1 GHz. The fabricated IDC with width and spacing of 1.5 and 1.8 μm, respectively, achieved tunability of 26% and a Q factor of 10 at 5.5 V.
Applied Physics Letters 05/2007; 90(18):182908-182908-3. · 3.84 Impact Factor
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ABSTRACT: In this paper, a tunable inter-digital capacitor (IDC) using the bismuth zinc niobate (BZN) pyrochlore thin film dielectrics is presented for microwave applications. In order to reduce the DC bias voltage and to increase the tunability of the IDC, its electrodes are fully embedded into the tunable BZN dielectrics. At 20 V DC applied, the IDC yields 75 % tunability at 5.8 GHz. This tunability is the highest at microwave frequencies, as far as authors know
Microwave Conference, 2006. 36th European; 10/2006
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ABSTRACT: Thin films of Bi2O3-ZnO-Nb2O5 system with cubic pyrochlore structure can be deposited using both cubic and monoclinic (zirconolite) targets. When monoclinic target was used, the as-deposited phase was nonequilibrium cubic monophase. After post-annealing in the 600–800^C range, phase decomposition occurred, resulting in more thermodynamically stable cubic pyrochlore and monoclinic zirconolite phases. The dielectric properties, such as dielectric constant and electric field dependent tunability, showed a steep increase along with phase separation. However, dielectric loss had a reverse tendency. The maximum tunability was about 38%, which exceeds that of cubic pyrochlore monophase films deposited from cubic target.
Journal of Electroceramics 06/2005; 14(3):171-175. · 1.19 Impact Factor
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ABSTRACT: Doped TiO(2) semiconductor powders were synthesized using Al and W as photovoltaic property-enhancing impurities. Al-doped TiO(2) electrodes increased open-circuit voltage (V(oc)), but reduced short-circuit current (I(sc)). In contrast, W-doped TiO(2) had an opposite effect. However, dye-sensitized solar cell efficiency fabricated with doped TiO(2) was remarkably better than that of undoped TiO(2). It seems that these phenomena were related to electrical surface-state modifications induced by metal-ion dopants. These modifications led to significant changes in powder aggregation, charge transfer kinetics, and dye adsorption characteristics. The highest efficiency was found by using (Al+W)-doped TiO(2) nanopowders.
Journal of Colloid and Interface Science 04/2005; 283(2):482-7. · 3.07 Impact Factor
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ABSTRACT: TiO2 film for use as dye-sensitized solar cell was prepared using the TiO2 colloidal sols (unpeptized sol and peptized sol). The optical properties and photocurrent-voltage characteristics of the resultant films were investigated. The optical transmittance of TiO2 thin film prepared from the peptized colloidal sol was over 90%, while that of TiO2 film from the unpeptized sol was under 80%. The TiO2 photoelectrode prepared from the peptized colloidal sol showed low photoelectric conversion efficiency (eta), 1.30%, whereas the efficiency of photoelectrode from the unpeptized sol was 2.21%. The high optical transmittance and low conversion efficiency of TiO2 film from the peptized sol are discussed in terms of dense microstructure due to the drying nature of well-dispersed colloidal sol.
Journal of Colloid and Interface Science 12/2004; 279(2):479-83. · 3.07 Impact Factor
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ABSTRACT: TiO(2) thin films were prepared using the dip-coating method with a polymeric sol including additives such as Al, W, and Al+W to examine two major properties: photocatalysis and hydrophilicity. W-doped films showed the best photocatalytic efficiency, while Al-doped film was poorer than undoped samples. However, good hydrophilicity in terms of saturation contact angle and surface conversion rate was found in Al- and (Al+W)-mixed-doped films. It was found that deep electron-hole traps and high surface acidity of W-doped TiO(2) thin film were the major factors in high photocatalytic efficiency. In addition, low surface acidities of Al- and (Al+W)-doped films provided better hydrophilicity than W-doped ones. However, the amount of [Ti(3+)] point defects on the surface was another major factor, probably the most important, in getting the best hydrophilicity. Conclusively, it seemed that many parts of the photocatalysis mechanism depend more on bulk-related properties than do those of hydrophilicity, which can be defined as an interfacial (surface) or near-surface-restricted process.
Journal of Colloid and Interface Science 12/2003; 267(1):127-31. · 3.07 Impact Factor
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ABSTRACT: (Bi3xZn2−3x)(ZnxNb2−x)O7 thin films (x=1/2 and 2/3) have potential great for tunable RF and microwave devices due to medium dielectric constant and low dielectric loss. The tunable dielectric properties of Bi-rich, (Bi1.5 Zn0.5)(Zn0.5 Nb1.5)O7 thin films were investigated. To make Bi-rich cubic pyrochlore thin films, Bi2O3–ZnO–Nb2O5 monoclinic pyrochlore ceramic targets were used in reactive RF magnetron sputtering process. Substrate heating was employed to improve surface morphology and tunability. As-deposited films were crystallized or amorphous state depending on substrate temperature. All films were annealed at 600°C ∼ 800°C for 3 hours in the air. There were no zinc niobate secondary phases in the films before and after post-annealing, while quite significant amount BZN thin films were found in sputtered using cubic pyrochlore ceramic targets, especially after post-annealing. It was found that Bi-rich BZN films have much larger tunability when as-deposited phase are amorphous. The maximum tunability 38% was obtained when substrate is heated to 350°C and composition of films is close to exact stoichiometric cubic BZN.
MRS Proceedings. 12/2002; 783.
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ABSTRACT: The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba0.7Sr0.3)TiO3 (BST) with the addition of AST (4Al2O3· 9SiO2· 3TiO2) is investigated in this paper. The AST–BST samples were characterized with optical microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well-known oxidation effects. With the aid of a brick-layer model and high-resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO3. Finally, the effect of precipitated (Ba,Sr)TiO3 on the PTCR characteristics is discussed in terms of the acceptor-state density and the polarization state at grain boundaries.
Journal of the American Ceramic Society 04/2002; 85(5):1173 - 1179. · 2.27 Impact Factor
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ABSTRACT: (1−x)ZnNb2O6·xTiO2 ceramics were prepared using both anatase and rutile forms of TiO2. At a composition of x= 0.58, a mixture region of ixiolite (ZnTiNb2O8) and rutile was observed and the temperature coefficient of resonant frequency (τf) was ∼0 ppm/°C. We found that although ɛr and τf were comparable, the quality factor (Q×f, Q≈ 1/ tan δ, f= resonant frequency) of 0.42ZnNb2O6·0.58TiO2 prepared from anatase and rutile was 6000 and 29 000, respectively. The origin of the difference in Q×f of both samples was investigated by measuring electrical conductivity and by analysis of the anatase–rutile phase transition. The anatase-derived sample had higher conductivity, which was related to the reduction of Ti4+. It is suggested that the increase of dielectric loss originates from an increase in Ti3+ and oxygen vacancies due to an anatase–rutile phase transition.
Journal of the American Ceramic Society 04/2002; 85(5):1169 - 1172. · 2.27 Impact Factor
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ABSTRACT: The BZN pyrochlore thin films were prepared on platinized Si substrates using a reactive RF magnetron sputtering. The structures, surface morphologies, dielectric properties and voltage tunable properties of films with deposition parameters were investigated. The BZN thin films have a cubic pyrochlore phase and secondary phases of zinc niobate, bismuth niobate when crystallized at 600° 800°. The dielectric constant and tunability of thin films are O2/Ar ratio and post-annealing temperature dependent. The BZN thin films sputtered in 15% O2 and annealed at 700° had a dielectric constant of 153, tan δof~0.003 and maximum tunability of 14% at 1,000kV/cm.
MRS Proceedings. 12/2001; 720.
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ABSTRACT: The effects of Nb2O5 and ZnO addition on the dielectric properties, especially the quality factor, of (Zr0.8Sn0.2)TiO4 (ZST) ceramics were investigated in terms of the sintered density acquired by the zinc. For ZST ceramics with 2 mol% added ZnO, the relative density of the samples decreased with >0.5 mol% addition of Nb2O5. On the other hand, for samples with 6 mol% added ZnO, the relative density remained >97%, even when the amount of Nb2O5 was increased to 2.0 mol%. When >0.5 mol% Nb2O5 was added, both the quality factor and the dielectric constant exhibited similar trends with sintered density. The ZST ceramics with 6 mol% added ZnO, especially, still manifested a quality factor >40 000 and a dielectric constant of 37, even when the amount of Nb2O5 was increased, values that are not explainable by the previously suggested electronic defect model.
Journal of the American Ceramic Society 10/2001; 84(11):2542 - 2546. · 2.27 Impact Factor
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ABSTRACT: The effect of CuO additions on the firing temperature of ZnNb2O6 ceramics was investigated using dilatometry, transmission electron microscopy, and X-ray diffractometry. A 5 wt% CuO addition to ZnNb2O6 ceramics significantly lowered the firing temperature from 1150° to ∼900°C. The presence of a CuO-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu2)Nb2O8. In particular, the low-fired ZnNb2O6 ceramics had good microwave dielectric characteristics—Q×f= 59 500, ɛr= 22.1, τf=–66 ppm/oC. These properties were correlated with the formation of a second phase, (ZnCu2)Nb2O8.
Journal of the American Ceramic Society 05/2001; 84(6):1286 - 1290. · 2.27 Impact Factor
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ABSTRACT: The relationship between hydrophilicity and surface morphology of TiO2 film was investigated. TiO2 films were deposited by MOCVD, and anatase films were crystallized. The rougher the surface of anatase film, the slower the conversion from hydrophilic to hydrophobic state. Also in some films, even the sonication could not accelerate the kinetics. However, the recovery rate to hydrophilicity under UV illumination had a reverse dependency on the surface roughness. It was assumed that the rougher TiO2 films could have a large concentration of Ti3+ generated by UV illumination on the surface, which plays a major role as adsorption sites of −OH in the water as well as in the air. Therefore, the healing kinetics of Ti3+ by oxygen in the air of a dark room could have been different among films with various surface roughnesses. Conclusively, the sustaining tendency of hydrophilic or hydrophobic properties could mainly depend on the concentration of Ti3+ by UV light, and in turn on the processing conditions of film deposition.
08/2000;
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ABSTRACT: Al–Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.
Applied Surface Science.
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ABSTRACT: The Bi2O3-ZnO-Nb2O5 (BZN) pyrochlore thin films were prepared on platinized Si substrates using a reactive rf magnetron sputtering. The structures, surface morphologies, dielectric properties and voltage tunable dielectric properties of films with deposition parameters were investigated. The sputter deposited BZN pyrochlore thin films have a cubic pyrochlore phase and secondary phases of zinc niobate and bismuth niobate when crystallized at 600∼800 °C. The dielectric constant and tunability of thin films changed with an O2/Ar ratio and post-annealing temperature. The BZN pyrochlore thin films sputtered in 15% O2 and annealed at 700 °C had a dielectric constant of 153, tan δ of ∼0.003 and maximum tunability of 14% at 1000 kV/cm of dc bias field under 1 MHz.
Thin Solid Films.
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ABSTRACT: In our present study, the effects of alcohol washing on the crystallization behavior of precipitated titanium oxide were investigated using Fourier-transformed infrared spectroscopy (FT-IR), thermogravimetry, differential scanning calorimetry, X-ray powder diffraction, and Raman spectroscopy. Alcohol rinsing of the precipitated titania powder having an amorphous hydrated form retarded its crystallization to the anatase phase. The crystallization temperature for 390°C of nonrinsed (water-washed only) powder was increased to 467°C with the alcohol rinse. The retardation was attributed to the formation of oxo-alkoxides on the particle surfaces. FT-IR analysis demonstrated that the alcohol-rinsed powder had a dehydration rate much lower than that of the nonrinsed powder as temperatures were increased. Therefore, it was suggested that the presence of oxo-alkoxides in the alcohol-rinsed powder decreased the dehydration rate, which, in turn, retarded crystallization to the anatase structure.
Journal of Colloid and Interface Science 211(2):321-325. · 3.07 Impact Factor
