Naoto Otake

Growth of YBa2Cu3O7-x Superconducting Thin Films on [111] Oriented Ag Films

YBa2Cu3O7-x (YBCO) superconducting thin film was prepared on a [111] oriented Ag film using off-axis rf magnetron-sputtering. The [111] oriented Ag film was prepared on the (001) single-crystal natural mica substrate at a substrate temperature of 200° C under argon atmosphere. The YBCO film grew with, not only a strong orientation for the c-axis, but also with the three-symmetrical orientation for a and b axes on the mica/Ag substrate without post-annealing. The full-width at half maximum (FWHM) intensity of the 003 ω-rocking curve of the YBCO film was 1.52°. The optimal substrate temperature was 620° C, when the partial pressure of oxygen was 1.0×10-2 Torr. T c (onset) and T c (zero) of the films were 84 K and 77 K, respectively, according to the AC magnetic susceptibility measurements. The J c of the film was measured by the conventional four-probe method, and the J c (J//ab) value was 1.4×104 A/cm2 at 77 K in a liquid nitrogen bath. The YBCO film showed the thickness dependence of T c to be due to the large lattice mismatch of Ag(111) to YBCO (001).

Micro Free-Form Fabrication of Aluminum Nitride and Zinc Oxide

Selective growth of aluminum nitride (AlN) and zinc oxide (ZnO) has been performed by an Ar-laser-enhanced reactive vapor deposition method on Si (100) substrates. The substrate was selectively heated by laser irradiation. Al and Zn were evaporated from Ta crucibles by an electron gun in NH3 and O2 atmospheres, respectively. The metal vapor reacted with atmospheric gas on the substrate surface due to laser heating, when the temperature of the laser-irradiated part was higher than 450°C for AlN and 230°C for ZnO. Not only the substrate temperature, but also the thickness of the Al and Zn layers, which are deposited during the time interval between the first laser irradiation and subsequent laser irradiation, was an important factor for realizing the selective growth. The critical thickness was found to be 0.2 nm and 6 nm for AlN and ZnO, respectively. Two-dimensional selective growth and three-dimensional micro free-form fabrication of AlN were performed under these conditions using a two-dimensional laser scanning setup. The AlN layer was successfully deposited in accordance with a laser drawing pattern, even when the drawing pattern changed during synthesis.

Segment-structured diamond-like carbon films for friction surface of surface acoustic wave linear motor

A surface acoustic wave (SAW) linear motor is a kind of ultrasonic motor, which has many merits such as thin structure, easy installation and so on. The motor, however, has a problem with wear of contact surface due to its driving principle. Diamond-like carbon (DLC) film has been recognized as a wear resistance material. In our research, segment-structured DLC (S-DLC) films were applied to the stator transducer surface. However, exfoliations of the S-DLC films and insufficient driving performance were observed. This paper proposes a new preparing method for the segment structure on the stator transducer and describes the prepared surface. Driving surface abrasion test result and increased driving characteristics are also reported. The reason why the driving performance was improved but not same as that of a conventional SAW linear motor is discussed. Friction coefficients are focused for the discussion.

Melt front surface asperity and welding-defect generation in ceramic injection molding

Abstract Melt front roughness was examined firstly, and it was found that an injected part is separated into two regions: a rough surface region and a fine surface region. The rough surface region results from melt front asperities generated by the blowout of voids at the front surface which are mixed into the material by jetting flow in the sprue. It was also found that voids in the sprue can be eliminated by applying counter-pressure. Secondly, the generation property of welding defects, weld line and voids, has been examined by counter-flow joining and their elimination criteria are obtained. It was shown that both criteria approximately coincide with each other. The welding-defect elimination criterion obtained is applied to the evaluation of welding-defect generation under various injection conditions and it was found that the criterion does not depend greatly on the asperities of the flow front. Furthermore, the criterion is also effective for estimating welding defects in injection molding using a mold cavity with inserts. Finally, it was confirmed that the above criterion approximately coincides with that in a previous paper which was obtained by the use of simple void-reducing conditions in the joining of green ceramic blocks with artificially grooved surfaces.

Analysis of Fiber Orientation and Velocity Distribution in Flow of Short Fiber-Polymer Melt Mixture through Cooled-Mold Slit Channel in Consideration with Fiber-Mold Wall Interaction.

In injection molding of short fiber-polymer melt mixture, influence of the interaction between a fiber and a mold wall on fiber distribution and flow property cannot be neglected, when fiber length is not very short comparatively to the thickness of a mold cavity. In the flow through a cooled mold cavity, solidifying layer grows and it affects that relation further. In this paper, effiects of these causes on fiber orientation and velocity distribution have been made clear by using numerical analysis, in which each fiber motion is analyzed from equilibrium conditions and fiber orientation distribution is obtained by integrating frequency of orientation angles of each fiber over the whole angles, and the following results have been obtained. (i) Near a mold wall, mixture is cooled and no flow layer is generated. On the other hand, apparent viscosity increases in the region, apart from a mold wall by more than half of fiber length, because of high fiber concentration, and plug flow-like velocity distribution is generated. (ii) Pressure gradient increases toward downstream in low injection rate, because of cooling of mixture, whereas it decreases in high injection rate, because of viscosity decrease due to shear heating. (iii) As fiber length decreases, pressure gradient decreases. (iv) Fiber orientation distribution changes considerably with injection rate change.

Numerical Analysis of Flow and Fiber Orientation in Slit Channel Flow of Short Fiber-Polymer Melt Mixture.

In injection molding of short fiber-polymer melt mixture, fiber-fiber interaction becomes large when fiber volume fraction increases. It leads to significant effect on the velocity field of the mixture and fiber orientation distribution. Fiber-mold wall interaction also has an effect on the mixture flow property, especially when fiber length is of the same order as the mold cavity thickness. In this paper, an isothermal flow of mixture through a slit channel and fiber orientation distribution in that flow are analyzed numerically in consideration with fiber-fiber interaction and fiber-mold wall interaction, and the following results are obtained: (1) In rather short distance from entrance of slit channel, fibers are rearranged rapidly and the flow becomes approximately steady after that. (2) When fiber volume fraction increases, the mixture flow tends to become plug-like one and pressure loss increases. (3) A layer of low fibers volume fraction is generated along mold wall due to fiber-mold wall interaction and, consequently, the pressure loss decreases. (4) Fluid velocity profile across cavity section in this paper is found to be approximately coincident with that obtained by using Shaqfehs viscosity model.