J.-G. Kim

PTCR characteristics in porous (Ba,Sr)TiO3 ceramics produced by adding partially oxidized Ti powders

Abstract Porous and fine-grained (Ba,Sr)TiO 3 ceramics were fabricated in vacuum by the addition of partially oxidized Ti powders. The positive temperature coefficient of resistivity (PTCR) characteristics in the (Ba,Sr)TiO 3 ceramics appeared after paste-baking treatment at 580°C in air due to the adsorption of oxygen at grain boundaries, in the same behavior as ordinary air-sintered BaTiO 3 ceramics. It was found that the phase transition temperature from the tetragonal to cubic structure of (Ba,Sr)TiO 3 ceramics depends on the oxygen content and grain size. The electrical properties of the (Ba,Sr)TiO 3 ceramics were discussed, based on the microstructure, resistivity of grain boundaries, donor concentration of grains, and the electrical potential barrier of grain boundaries. The (Ba,Sr)TiO 3 ceramics containing the 5 vol.% partially oxidized Ti powders sintered at 1450°C showed a large PTCR effect greater than six orders of magnitude.

Effect of atmosphere on the PTCR characteristics of porous (Ba,Sr)TiO3 ceramics

Porous and fine-grained (Ba,Sr)TiO3 ceramics were fabricated by adding partially oxidized Ti powders. During heating and cooling, the electrical resistance was measured in air, O2, N2, and H2 atmospheres and in H2 followed by air atmosphere. The effect of atmosphere on the PTCR characteristics and the role of oxygen on the grain-boundaries in the PTCR characteristics were investigated. The porous (Ba,Sr)TiO3 ceramics showed a large PTCR effect, which was strongly sensitive to atmosphere. This effect was increased in oxidizing atmosphere mainly because of an increase in potential barrier height whereas decreased in reducing atmosphere mainly because of a decrease in potential barrier height.

Photocatalytic Properties of the Transition Metal Doped TiO2 Powder Prepared by Sol-Gel Process

Transition metal-doped TiO2 powders as a photocatalyst were prepared by sol-gel process and Sb, Bi and Nb were introduced into them as dopants. The photocatalytic behaviors of the doped TiO2 powder were studied as a function of dopant, doping concentration and preparation conditions. X-ray diffraction, FT-Raman, B.E.T. and scanning electron microscopy were applied for structural and microstructural studies. Optical properties of the doped TiO2 powders were studied by UV-Visible Spectrometer and photocatalytic activity of the doped TiO2 was characterized in terms of the degradation of 1,4-dichlorobenzene. X-ray difraction analysis showed that doping with a transition metal ion suppresses anatase-to-rutile phase transition compared with the pure TiO2. The Sb and Nb-doped TiO2 powders did not exhibit any other diffraction peaks except those belonging to TiO2. On the other hand, a diffraction peak of Bi4Ti3O12 appears for 5 at.% Bi-doped samples. All of the doped TiO2 powders had higher specific surface area than undoped TiO2. Surface area increased with increasing dopant concentration depending on the dopant, from 33.9 m2/g to 55.4m2/g. The UV-visible absorption spectra of doped samples were red-shifted by 20~50nm according to the doping level. Also transition metal doped TiO2 powders exhibited better photocatalytic activity than the undoped TiO2. The increase in photoactivity is probably due to the increase in the interfacial electron transfer, red shifts, and better crystallinity.

Microstructure and electrical properties of porous (Ba, Sr)TiO3 ceramics

Abstract Porous and fine-grained (Ba,Sr)TiO 3 ceramics were fabricated by the addition of partially oxidized Ti or Ti powders into the (Ba,Sr)TiO 3 powders. The crystalline structure of the porous (Ba,Sr)TiO 3 ceramics was strongly dependent on the oxygen contents. The room-temperature crystalline structure of the vacuum-sintered (Ba,Sr)TiO 3 was cubic, while that of the vacuum-sintered and then paste-baking treated (Ba,Sr)TiO 3 was tetragonal. The paste-baking treated (Ba,Sr)TiO 3 , containing 5–7 vol.% partially oxidized Ti, showed the excellent positive temperature coefficient of resistivity (PTCR) characteristics.

Plasma etching for the application to low-k dielectrics devices

We present a study of the photoresist (PR) etching and the low-k materials damage using a ferrite-core inductively coupled plasma (ICP) etcher, in order to develop an etching process for the low-k dielectric devices. We reveal that the N2/O2 flow ratio and bias power affected the PR etching rate. By Fourier transform infrared spectroscopy and HF dipping test, we investigated the effect of the gas flow ratio and bias power on the amount of etching damage to the low-k material.

Effect of atmosphere on the PTCR characteristics of porous Ba(Ti,Sb)O3 ceramics produced by adding corn-starch

Porous Ba(Ti,Sb)O3 ceramics were fabricated by adding corn-starch at 20 wt %. The effect of atmosphere on the PTCR characteristics of the porous Ba(Ti,Sb)O3 ceramics and the role of oxygen on the grain boundaries in the PTCR characteristics of the Ba(Ti,Sb)O3 ceramics were investigated. In air, O2, N2, and H2 atmospheres, the electrical resistivity of Ba(Ti,Sb)O3 ceramics below 150 °C was independent of atmosphere, while it was strongly dependent on atmosphere above 200 °C. The low electrical resistivity in reducing atmospheres was due to a decrease in potential barrier height, which originated from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In a N2 atmosphere, the electrical resistivity of Ba(Ti,Sb)O3 ceramics during the cooling cycle was lower than that during the heating cycle, and then the electrical resistivity of the porous Ba(Ti,Sb)O3 ceramics during subsequent heating and cooling cycles was increased again by exposure to an O2 atmosphere.

Catalyst-Free Growth of Tin Oxide One-Dimensional Nanostructures on Silicon Nitride Substrates

We have obtained one-dimensional (1D) nanomaterials of tin oxide (SnO2) on silicon nitride (Si3N4)-coated Si substrates by carrying out the thermal evaporation of solid Sn powders and varying the substrate temperature in an Ar/O2 ambient gas. We analyzed the samples with scanning electron microscopy, X-ray diffraction, transmission electron microscopy and photoluminescence (PL). Reactions at a lower substrate temperature gave rise to thinner 1D structures. The obtained 1D nanomaterials were single crystalline with a tetragonal rutile structure. We proposed a vapor-solid process as the growth mechanism for SnO2 nanorods. The PL spectrum exhibited visible light emission.

Nanostructural and Optical Features of nc-Si:H Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition Techniques

The nanostructural and optical features of hydrogenated nanocrystalline silicon (nc-Si:H) thin films, which were prepared by plasma enhanced chemical vapor deposition (PECVD), were investigated as a function of deposition conditions. It was found that the crystallite size varied with the relative fraction of Si-H3 bonds in the films, [ ] eger n n n H Si H Si int 3 1 3 / ] [ = = ∑ − − , which was sensitively related with the flow rate of SiH4 reaction gas. The silicon nanocrystallites in the films enlarged from ~2.0 to ~8.0 nm in their size with increasing gas flow rate, while the PL emission energy varied from 2.5 to 1.8 eV; the relative fractions of the Si-H3, Si-H2, and Si-H bonds in the amorphous matrix were also varied sensitively with the SiH4 flow rate. A model for the nanostructure of the nc-Si:H films was suggested to discribe the variations in the size and chemical bonds of the nanocrystallites as well as the amorphous matrix depending on the deposition conditions.

Effect of partially oxidized Ti powders on the microstructure and PTCR characteristics of (Ba, Sr)TiO3

Rutile TiO2 (a=4.594 å and c=2.958 å) phase was formed on the outer region of Ti powders after oxidation at 600 °C for 1–300 h. Porous (Ba,Sr)TiO3 ceramics were fabricated by adding partially oxidized Ti powders (4–8 vol %) into (Ba,Sr)TiO3 powders, and showed excellent positive temperature coefficient of resistivity (PTCR) characteristics after paste-baking treatment at 580 °C in air. The PTCR characteristics of the porous ceramics were mainly attributed to the adsorption of oxygen at the grain boundaries. The microstructure and electrical properties of the porous (Ba,Sr)TiO3 ceramics containing the partially oxidized Ti powders oxidized at 600 °C for different oxidation times (1–300 h) were investigated.