Preparation of lightweight hollow glass microsphere ceramics by gel casting

Owing to low density, hollow glass microspheres (HGMs) float on common media such as water, ethanol, and tertiary butanol. As a result, HGMs are not suitable to prepare slurries and ceramics by gel, slip, and freeze castings. In this paper, polyacrylamide (PAM) was used as dispersant and thickener agent to prepare homogeneous HGM aqueous slurries with controlled solid loadings and subsequent lightweight HGM porous ceramics were prepared by gel casting. Effects of PAM content on the stability of aqueous slurries as well as effects of solid (i.e., HGM) loading on density, porosity, pore size distribution, and compressive strength of porous ceramics were investigated. Increasing the viscosity of the slurry resulted in HGMs with significantly lower floating rates and more stable HGM aqueous slurries. HGM porous ceramics with densities and compressive strengths of 0.127–0.219?g/cm³ and 0.74–1.71?MPa, respectively, were prepared by gel casting.     

The improvement of mechanical and dielectric properties of ordered mesoporous silica film using TEOS–MTES mixed silica precursor

Due to the rapid decrease in physical dimension of today's devices, lower resistive metal and/or lower dielectric constant material have to be applied. Recently, ordered mesoporous silica film has been drawn an attention for low-k application due to its ordered pore structure. However, it has been more required that low-k dielectrics should have low leakage current, high breakdown strength and high mechanical stabilities. In this study, ordered mesoporous silica films were prepared by sol–gel process using tetraethylorthosilane and methyltriethoxysilane as a mixed silica precursor in order to increase the mechanical and dielectric properties. It was found that the properties of the films were improved when the pore ordering and the amount of the incorporated methyl ligand were maximized.     

Porous YSZ ceramics with unidirectionally aligned pore channel structure: Lowering thermal conductivity by silica aerogels impregnation

The previous report of this work has demonstrated the fabrication and properties of porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels. As a follow-up study, the present work aims at lowering the thermal conductivity of the porous YSZ ceramics by silica aerogels impregnation. The porous YSZ ceramics were immersed in an about-to-gel silica sol. Both the unidirectionally aligned pore channels and the inter-grain pores by grain stacking in the channel-pore wall of the porous YSZ ceramics were impregnated with the silica sol. After aging and supercritical drying, silica aerogels formed in the macroporous network of the porous YSZ ceramics with unidirectionally aligned pore channels. The influences of silica aerogel impregnation on the microstructure and properties of porous YSZ ceramics with unidirectional aligned pore channels were investigated. The porosity decreased after impregnation with silica aerogels. Both microstructure observation and pore size distribution indicated that both channel-pore size and inter-grain pore-size decreased significantly after impregnation with silica aerogels. Impregnating porous YSZ ceramics with silica aerogels remarkably lowered the room-temperature thermal conductivity and enhanced the compressive strength. The as-fabricated materials are thus suitable for applications in bulk thermal isolators.     

Electrical resistivity of porcelain bodies with natural zeolite addition

In this study, the effect of natural zeolite addition on the electrical properties of porcelain bodies was investigated. Clinoptilolite, which is a type of natural zeolite, was added partially or fully in replacement of quartz in selected electro-porcelain compositions. Samples were fired in an electric furnace with a heating rate of 10 °C/min at 1200 and 1250 °C with a period of 60 min. The electrical resistance measurements of samples were performed at 50, 200, 400 and 600 °C. It was shown that the resistivity of samples increased at 50 °C temperature after zeolite addition, while it was decreasing after zeolite addition at higher temperatures. At the same time, it was recognized that the resistivity of samples depends on sintering temperature. The activation energy of electrical resistivity of samples was found to be in the range of 0.79–0.87 eV.     

Single crystal and transparent ceramic Nd-doped oxide laser materials: a comparative spectroscopic investigation

The high resolution spectroscopy indicates that the spectroscopic and emission dynamics properties of cubic oxide transparent ceramics (Nd:YAG and Nd:Y₂O₃) produced by the method of solid-state mixing of oxides are similar to those of the single crystals. The ability of these ceramics to incorporate very high concentrations of Nd (10 at.%) enables a considerable extension of the knowledge of these systems. These studies reveal that for the whole range of Nd concentrations the distribution of the Nd ions at the available substitution sites in these ceramics is random over the whole body of the crystalline ceramic grains and no regions of enhanced concentration are evident. Coupled with the structural, mechanical and thermal properties and with the lower fabrication cost and the enhanced versatility in the control of composition and size, these ceramics are a viable alternative for the crystalline materials in construction of solid-state lasers.     

What makes the luminescence of Prdifferent in CaTiO3 and CaZrO3 ?

Although orthorhombic CaZrO₃ and CaTiO₃ perovskites are characterised by very similar structural features, they show different luminescence properties when doped with Pr³⁺ ions: the former exhibits the typical greenish-blue ³P₀→³H₄ emission, while the latter shows a single red ¹D₂→³H₄ luminescence. The explanation of this difference requires to understand the mechanism responsible for total quenching of ³P₀ emission in CaTiO₃ host. Among the different possible relaxation pathways from ³P₀ to ¹D₂, intersystem crossing through low lying 4f¹5d¹ levels has been proposed in a previous study. Owing to new spectroscopic results on CaZrO₃:Pr³⁺ and CaTiO₃:Pr³⁺, the role of the 4f5d band is reconsidered and an alternative relaxation channel is proposed via low lying intervalence charge transfer state.     

Dielectric relaxation in calcium titanate-containing ceramics prepared by plasma spraying

The relative permittivity and loss factor frequency dependence in a weak electric field of plasma sprayed perovskite and ilminite polycrystalline ceramic materials—pure synthetic calcium titanate, as well as magnesium titanate—calcium titanate mixture, were studied. It was observed that plasma-sprayed titanates exhibit a strong relaxation of permittivity and loss factor decrease when they are measured in an as-sprayed state. The frequency dependence of the earlier properties is influenced by chemical composition and spraying parameters, but the relaxation character in general is preserved in all cases. The volume resistivity of the samples in an as-sprayed as well as subsequently annealed state was studied also. Several aspects of the structural features of plasma deposits and their possible influence on dielectric properties are discussed.     

Ion-beam-induced insulator deposition for chip circuit modification

As semiconductor manufacturing technologies become more complex and the number of metallization levels increases, the complexity of chip circuit modification using focused ion beam technology has also increased. The fabrication of an insulating film in a localized region to protect exposed metal greatly enhances the modification capability. It is often necessary to remove a portion of an overlying metal line to gain access to an underlying area of interest. To maintain functionality, this overlying metal line must be reconnected without shorting to underlying metallurgy.

We have developed an ion-beam-induced process for circuit modification which uses an oxygen and siloxane precursor. Test structures were fabricated to evaluate the electrical integrity of these films. Results indicating sufficient dielectric strength for both memory and logic applications and the material analysis of this insulator film, are presented.     

Photo patternable porous siloxane thin films using cyclodextrins as template materials

Photo patternable cyclic silsesquioxane (mCSSQ) compositions containing heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (tCD) as a porogen and photo acid generator (PAG) have been prepared, with the goal of achieving a photo resist free porous low dielectric constant precursor. The composition containing triphenylsulfonium based PAG could effectively create a patterned mCSSQ thin film with a resolution approaching ∼2 μm. The pore size of the mCSSQ film with PAG was smaller than that without PAG. Furthermore, the pore size distribution of the mCSSQ film with PAG was much narrower than that without PAG. This might be attributed to the disturbance effect of the agglomeration of tCD molecules through pre-vitrification of the matrix at the relatively low curing temperature. The mechanical property and dielectric constant of the photo-definable mCSSQ/tCD/PAG film were comparable to those of the mCSSQ/tCD counterpart.     

Photoconductors based on ZnxCd1−xS and CdSe1−ySy thin films, fabricated with multilayer structure

Photoconductors based on evaporated Zn_xCd_1−xS and CdSe_1−yS_y thin films, with a novel multilayer structure, were fabricated and characterized through spectral response measurements. The device structure is constituted by several layers of different energy gaps, sequentially deposited side by side and interconnected in series or in parallel. The influence of the preparation conditions, number of layers and electrode configuration, on the performance of the photoconductors was determined. Photoresistors with a detection range between 400 and 750 nm were developed, using four layers with energy gaps varying between 1.8 eV and 2.8 eV and interconnected in parallel.