Won n Seo

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.

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.

Huge thermopower of porous Y2O3

Porous Y2O3 ceramic was found to show huge thermopower values up to −50 mV/K at 900–1000 K in vacuum, but not in air. Such huge thermopowers may be generated by the electron gas emitted from the internal surfaces of the pores and are associated with some unknown effects. The nondimensional thermoelectric figure of merit, ZT, of this porous ceramic was as large as ∼0.95 at ∼950 K, and hence, it can be used as a thermoelectric material.

Two-dimensional arrangement of fine silica spheres on self-assembled monolayers

Abstract Novel processes to arrange fine silica spheres two-dimensionally on self-assembled monolayers (SAMs) were developed. SiO2 sphere surfaces were modified to have CN groups by the use of trichlorocyanoethylsilane, and CN groups were oxidized to COOH groups with t-BuOK. A SAM of PTCS (phenyltrichlorosilane) was modified to have a phenyl/silanol-group pattern by UV irradiation using a photomask and was used as a template to arrange fine SiO2 spheres. SiO2 spheres were selectively attached to silanol surfaces, possibly forming ester bonds, which enabled the fabrication of micropatterned arrangements of SiO2 spheres.

Condenson state and its effects on thermoelectric properties in In4Se3

The thermoelectric properties of In4Se3 compounds were investigated, and their unique charge and thermal transport behaviours were interpreted in terms of condenson state for the first time. The effects of Sn-doping both on the carrier localization and lattice thermal conductivity were consistent with the proposed condenson model. Some important physical properties, such as the band gap energy of In4Se3 and the binding energy of the condenson state, are also presented.

Wear of UHMWPE against Zirconia/Alumina Composite

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and on the conventional ceramics (alumina and zirconia) used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more in the linear reciprocal sliding test than in the repeat pass rotational sliding test for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as the alternative materials for femoral head in total hip joint replacement.

Neural Cells on Iridium Oxide

Iridium oxide was investigated as a material for the stimula ting neural electrode. Iridium oxide was formed by potential sweep of iridium film that was deposi ted on either Si wafer or silicone rubber with electron-beam evaporation. The rate of iridium oxide format ion was dependent on the upper and lower limits of potential sweep. The higher thickness of iri dium oxide produced the higher charge injection due to the reversible valence transition of iridium within oxide. Embryonic cortical neural cells formed neurofilament after 4-day culture on iridium oxi de, which indicated neural cells could adhere and survive on iridium oxide. Introduction Interaction between neurons and electrodes is very important for stim ulation or signal collection. The restoration of a variety of physiological functions by electricall y ctivating nerves serving paralyzed muscles has been of particular interest. The first application of functional electrical stimulation (FES) was by Liberson [1] who stimulated the peroneal nerve in adult hemipleg ia to correct drop foot during the swing phase of locomotion. For the rehabilitation of locomotion in parapl egics and hemiplegics, thirty-two electrodes are required and even more stimulations are demanded for the refined control [2]. A major problem limiting the widespread application FES has been the lack of stimulating electrodes that can be used for long-term precise multipoint stimulation of nerve s. Practical application requires miniaturized electrode geometry, which still demands high charge i njection capability over the suitable range in potential. Recently, iridium oxide was investigat ed s a candidate electrode material [3-6]. Iridium oxide shows electrochromic behavior, where a change of col r takes place between oxidative and reductive state of iridum. The color of iridium oxide st art changing from metallic to blue around 0.4 V (SHE) in 0.1 M H 2SO4, become darker and remains dark blue above near 0.9 V (SHE). The bleaching process occurrs during the cathodic sweep. The dar k blue became lightened around 1.0 V (SHE) and no blue color could be observed below 0.4 V (SHE). The double proton-electron injection mechanism has been proposed to explain the elect rochromism of the anodic iridium oxide film by Gottesfeld et al. [7]. They postulated the fol lowing reaction to describe the film conversion processes: Ir(OH)n Irx(OH)n-x + xH + + xe In this mechanism, during the coloration process, electrons are removed fr m the oxide across the metal-oxide interface by application of a suitable anodic potential to the metal substrate. Charge repulsion causes an equivalent amount of mobile positive charge carrier s (protons) to be ejected Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 805-808 doi:10.4028/www.scientific.net/KEM.254-256.805

Wear Behaviors of UHMWPE against LTD-Free Zirconia/Alumina Composites

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on four different compositions of novel low temperature degradation-free zirconia/alumina (Z/A) composite material used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these Z/A composite disks were evaluated by performing the linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The novel low temperature degradation (LTD)-free tetragonal zirconia polycrystal (TZP)/alumina composite (90(5.3Y, 4.6Nb)-TZP/10Al2O3) induced the less wear amount of UHMWPE than the other Z/A composites. Linear reciprocal motion wore more the UHMWPE pin than did repeat pass rotational motion for all disk materials. It was observed that few transfer film on the sliding track of Z/A composite disks and the matching contact surfaces of pins had relatively less scratch. Getting rid of transfer film, there is no change of surface roughness on the sliding track of Z/A composite disks. This novel Z/A composite (90(5.3Y, 4.6Nb)-TZP/10 Al2O3) demonstrates the potential as an alternative material for the femoral head in total hip replacement.

Enhancement in the rate of the top seeded solution growth of SiC crystals via a roughening of the graphite surface

With the top seeded solution growth (TSSG) method, SiC crystals are grown in a Si–C solution where the dissolved C is supplied from graphite crucibles. In this study, the reactivity of the graphite was enhanced by roughening the surface to form a SiC interlayer, the intermediate compound in the dissolution of C to a Si melt. As a result, we clearly observed an enhancement in the growth rate by roughening the graphite surface in the crystal growth of SiC using TSSG method.