A study of deposition of ITO films on organic layer using facing target sputtering in Ar and Kr gases

In this study, the effects of sputtering gases on the damage to an organic layer (aluminum (III) bis(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq)) were investigated in the deposition of indium-tin oxide (ITO) films by using a facing target sputtering (FTS) system. Only a small improvement in the PL intensity of the BAlq layer was observed when the sputtering gas was changed from Ar to Kr gas. It was also found that suppression of the high-energy γ-electron bombardment to the substrate is very important to reduce the damages in the BAlq layers. In addition, a remarkable improvement in the PL intensity was observed by the increase in the sputtering gas pressure from 0.3 to 1.3 Pa. These results suggest that bombardment of reflected neutral gas atoms is not the main source of the damage that BAlq layer has, but the bombardment of high-energy sputtered atoms plays an important role for the remnant damages caused by the sputter-deposition of the ITO film at a low gas pressure, since the decrease in the PL intensity was almost totally suppressed by increasing the sputtering gas pressure above 1.1 Pa. Finally, low-damage sputter-deposition of ITO film with low resistivity on BAlq layer was achieved by completely suppressing the bombardment of high-energy particles, including γ-electrons, negative oxygen ions and high-energy sputter-emitted particles.     

Distribution of tensile property and microstructure in friction stir weld of 6063 aluminum

Dominant microstructural factors governing the global tensile properties of a friction-stir-welded joint of 6063 aluminum were examined by estimating distribution of local tensile properties corresponding to local microstructure and hardness. Yield and ultimate tensile strengths of the as-welded weld were significantly lower than those of the base material. Postweld aging and postweld solution heat-treatment and aging (SHTA) restored the strengths of the weld to the levels of the base material. Elongation was found to increase with increasing strength. Hardness tests showed that the as-welded weld was soft around the weld center and that the aged weld and the SHTA weld had relatively homogeneous distributions of high hardness. Hardness profiles of the welds were explained by precipitate distributions and precipitation sequences during the postweld heat treatments. The strengths of the welds were related to each minimum hardness value. In a weld having a heterogeneous hardness profile, the fracture occurred in the region with minimum hardness. When a weld had a homogeneous hardness profile, its fracture site depended on both crystallographic-orientation distribution of the matrix grains and strain tensor of the imposed deformation, i.e., it fractured in the region with a minimum average Taylor factor.     

Chemical and photoluminescence analyses of new carbon-based boron oxynitride phosphors

Analyses of newly developed carbon-based boron oxynitride phosphors using an electron energy-loss spectrometer and a spectroflurophotometer were carried out. The results showed that the prepared phosphor powder has covalently bonded boron, nitrogen, and oxygen atoms with a soft carbon framework. Photoluminescence characterization revealed that the resultant phosphor has a direct bandgap transition with defect broadened band edges, resulting in a high quantum efficiency, because the atomic distances of the phosphor are smaller than those of conventional carbon-based boron nitride compounds, which have an indirect bandgap transition and a low quantum efficiency. The atomic distances of the phosphor are smaller owing to the presence of oxygen atoms, which have a higher electron affinity and a smaller covalent bond radius compared with boron, carbon and nitrogen.     

Convergence and refinement of the Wang-Landau algorithm

Recently, Wang and Landau proposed a new random walk algorithm that can be very efficiently applied to many problems. Subsequently, there has been numerous studies on the algorithm itself and many proposals for improvements were put forward. However, fundamental questions such as what determines the rate of convergence has not been answered. To understand the mechanism behind the Wang-Landau method, we did an error analysis and found that a steady state is reached where the fluctuations in the accumulated energy histogram saturate at values proportional to [log(f)]^−1/2. This value is closely related to the error corrections to the Wang-Landau method. We also study the rate of convergence using different “tuning” parameters in the algorithm.     

Stacked-lamellar structure of electrospun poly(heptamethylene terephthalate) nanofibers

Poly(heptamethylene terephthalate) (poly(7GT)), which is an aromatic polyesters was synthesized, and nanofibers of poly(7GT) were prepared via electrospinning from its solution in 1,1,1,3,3,3-hexafluoro-2-propanol. Uniaxially oriented thin films were also prepared by applying shear strain to molten poly(7GT). Morphology of as-spun and annealed nanofibers and that of uniaxially oriented thin films were investigated by transmission electron microscopy. Selected-area electron diffraction (SAED) of bundles of the annealed nanofibers gave a highly oriented fiber pattern. In addition, dark-field images of the poly(7GT) nanofibers, which had been annealed at 85 °C for 48 h, were taken by using some of the reflections on/near the equator. The images showed a stacked-lamellar structure, in which crystalline lamellae appearing as bright striations oriented perpendicularly to the fiber axis were stacked in the direction of the fiber axis, and the corresponding average long period was estimated at about 19 nm. As for the uniaxially oriented thin films, SAED also gave an oriented fiber pattern. When the annealing of the films was performed similar to nanofibers, crystallization occurred and a stacked-lamellar structure was constructed parallel to the shearing direction. The corresponding average long period was estimated at about 27 nm. By comparing the fiber patterns between annealed nanofibers and thin films, it seems that electrospinning is more effective than uniaxial stretching in enhancing the molecular orientation in the case of poly(7GT).     

Ab initio molecular dynamics simulation for the insertion process of Si and Ca atoms into C74

A large-scale ab initio molecular dynamics simulation for the insertion process of silicon and calcium atoms into C₇₄ is carried out for the first time by using the all-electron mixed-basis approach, where a one-electron wave function is expressed by superposing plane waves and numerical atomic orbitals. The present numerical results show that a silicon atom with more than a 40 eV kinetic energy can be inserted into C₇₄ through the center of a six-membered ring with a very short relaxation time of about 40 fs, and a calcium atom can be inserted with a 120 eV kinetic energy with a rather long relaxation time (>540 fs).     

Microtexture in the friction-stir weld of an aluminum alloy

In order to characterize plastic flow during friction-stir welding, the microtextures in a friction-stir weld of the precipitation-hardened aluminum alloy 6063 have been analyzed by orientation imaging microscopy (OIM). The base-material plate has a Goss orientation. The weld center region, except for the upper surface, takes a typical shear texture component with two types of orientations. The orientations have a pair of common {111} and 〈110〉 parallel to the cylindrical pin surface and transverse direction of the plate, respectively. The typical texture component is also observed around the weld center on the midsection, although it rotates about the plate normal direction. A microtexture analysis after postweld heat treatment has suggested that dynamic recrystallization during friction-stir welding generates the recrystallized grains at the weld center.     

SEC-MALS characterization of cyclization reaction products: Formation of knotted ring polymer

Cyclization reaction products by the end-to-end ring closure of telechelic polystyrenes (PSs) with molecular weight of 47 k and 380 k in THF (good solvent) and also in cyclohexane (poor solvent) were characterized by SEC connected with multi-angle light scattering (MALS). By comparison of the SEC peaks of the monomeric rings from 47 k-PSs in THF and cyclohexane, there is no essential difference both in molecular weight and in molecular weight distribution between the two monomeric rings formed. On the other hand, comparing the data for monomeric rings from 380 k-PSs in THF and cyclohexane by SEC-MALS, it has been found that the ring formed in cyclohexane has the same molecular weight as that of the ring formed in THF, while the former reveals the lower radius of gyration than that of the ring formed in THF. These results clearly indicate the evidence of the formation of knotted ring polymers by experiment for the first time.     

Dose-dependent hypocholesterolemic actions of dietary apple polyphenol in rats fed cholesterol

The dose-dependent hypocholesterolemic and antiatherogenic effects of dietary apple polyphenol (AP) from unripe apple, which contains approximately 85% catechin oligomers (procyanidins), were examined in male Sprague-Dawley rats (4 wk of age) given a purified diet containing 0.5% cholesterol. Dietary AP at 0.5 and 1.0% levels significantly decreased the liver cholesterol level compared with that in the control (AP-free dietfed) group. Dietary AP also significantly lowered the serum cholesterol level compared with that in the control group. However, the HDL cholesterol level was significantly higher in the 1.0% AP fed group than in the control group. Accordingly, the ratio of HDL-cholesterol/total cholesterol was significantly higher in the 0.5% AP-fed group and 1.0% AP-fed group than in the control group. Moreover, the atherogenic indices in the 0.5 and 1.0% AP-fed groups were significantly lower than those in the control group. The activity of hepatic cholesterol 7α-hydroxylase tended to be increased by dietary AP in a dose-dependent manner. In accord with this observation, dietary AP increased the excretion of acidic steroids in feces. Dietary AP also significantly promoted the fecal excretion of neutral steroids in a dose-dependent manner. These observations suggest that dietary AP at 0.5 or 1.0% level exerts hypocholesterolemic and antiatherogenic effects through the promotion of cholesterol catabolism and inhibition of intestinal absorption of cholesterol.