Effect of Vacancy Distribution on the Thermal Conductivity of Ga<Subscript>2</Subscript>Te<Subscript>3</Subscript> and Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Our group has focused attention on Ga₂Te₃ as a natural nanostructured thermoelectric material. Ga₂Te₃ has basically a zincblende structure, but one-third of the Ga sites are structural vacancies due to the valence mismatch between Ga and Te. It has been confirmed that (1) vacancies in Ga₂Te₃ exist as two-dimensional (2D) vacancy planes, and (2) Ga₂Te₃ exhibits an unexpectedly low thermal conductivity (κ), most likely due to highly effective phonon scattering by the 2D vacancy planes. However, the effect of the size and periodicity of the 2D vacancy planes on κ has been unclear. In addition, it has also been unclear whether only the 2D vacancy planes reduce κ or if point-type vacancies can also reduce κ. In the present study, we tried to prepare Ga₂Te₃ and Ga₂Se₃ with various vacancy distributions by controlling annealing conditions. The atomic structures of the samples were characterized by means of transmission electron microscopy, and κ was evaluated from the thermal diffusivity measured by the laser flash method. The effects of vacancy distributions on κ of Ga₂Te₃ and Ga₂Se₃ are discussed.     

Electrical Properties of Isotropic Conductive Adhesives Composed of Silicone-Based Elastomer Binders Containing Ag Particles

The electrical properties of isotropic conductive adhesives (ICAs) with two different types of silicone-based binder containing Ag particles were examined. The ICAs were printed on glass substrates in order to prepare specimens for evaluating the electrical properties. In the case of adhesives containing a denatured silicone binder, both the curing and cooling steps in the isothermal curing process generated electrical conductivity. Adhesives that were cured at 120°C to 200°C exhibited similar values of electrical resistivity regardless of the different curing temperatures. By contrast, electrical conductivity was generated only during the cooling step when adhesives containing a dimethyl methylvinyl siloxane were isothermally cured. In this case, adhesives cured above 160°C exhibited high electrical resistivity. In evaluating the temperature dependence of the electrical resistivity, we found physical annealing to have significantly different effects on these specimens. In addition, we were able to make small sensitive variations in the properties of silicone-based ICAs by controlling the isothermal annealing and thermal cycling processes.     

Thermoelectric Properties of Ca3Co4-x Ga x O9+δ Prepared by Thermal Hydro-decomposition

The polycrystalline samples of Ca₃Co_4-x Ga _x O_9+δ (0 ≤ x ≤ 0.15) were prepared by a simple thermal hydro-decomposition method. The high density ceramics were fabricated using a spark plasma sintering technique. The crystal structure of calcined powders was characterized by x-ray diffraction. The single phase of Ca₃Co_4-x Ga _x O_9+δ was obtained. The scanning electron micrograph illustrated the grain alignment perpendicular to the direction of the pressure in the sintering process. The evidence from x-ray absorption near edge spectra were used to confirm the oxidation state of the Ga dopant. The thermoelectric properties of the misfit-layered of Ca₃Co_4-x Ga _x O_9+δ were investigated. Seebeck coefficient tended to decrease with increasing Ga content due to the hole-doping effect. The electrical resistivity and thermal conductivity were monotonically decreased with increasing Ga content. The Ga doping of x = 0.15 showed the highest power factor of 3.99 × 10^-4 W/mK² at 1,023 K and the lowest thermal conductivity of 1.45 W/mK at 1,073 K. This resulted in the highest ZT of 0.29 at 1,073 K. From the optical absorption spectra, the electronic structure near the Fermi level show no significant change with Ga doping.     

Direct Growth of Germanene at Interfaces between Van der Waals Materials and Ag(111)

Germanene, a 2D honeycomb germanium crystal, is grown at graphene/Ag(111) and hexagonal boron nitride (h-BN)/Ag(111) interfaces by segregating germanium atoms. A simple annealing process in N₂ or H₂/Ar at ambient pressure leads to the formation of germanene, indicating that an ultrahigh-vacuum condition is not necessary. The grown germanene is stable in air and uniform over the entire area covered with a van der Waals (vdW) material. As an important finding, it is necessary to use a vdW material as a cap layer for the present germanene growth method since the use of an Al₂O₃ cap layer results in no germanene formation. The present study also proves that Raman spectroscopy in air is a powerful tool for characterizing germanene at the interfaces, which is concluded by multiple analyses including first-principles density functional theory calculations. The direct growth of h-BN-capped germanene on Ag(111), which is demonstrated in the present study, is considered to be a promising technique for the fabrication of future germanene-based electronic devices.     

Failure-analysis-based test chip design for quick yield improvement

A new design approach for a test chip developed to shorten the debugging cycle time in fabrication is described. This approach meets the requirements for failure analysis as well as parametric and statistical analyses. Particular attention is devoted to accurate defect density estimation and to locating individual defects. This is done by designing test structures suitable for both electrical measurements and failure analysis. A specially designed test chip, named YTEG, is used to evaluate 0.5-μm CMOS process technologies, and confirms the effectiveness of the chip.     

图像的情感特征分析及其和谐感评价

情感信息处理是日本、美国等科学技术发达国家正着手研究的前沿课题,本文以图像的情感信息为研究对象,首先建立了二维波动的数学模型,然后提出了一种图像波动分析的方法,并用SD尺度法对三类典型波动规律的图像进行了心理测试,同时使用方差分析法验证了心理测试结果差异的显著性.证明了符合“1/f波动”规律的图像能够给人以和谐与美的感觉.     

Extending transmission bandwidth of air-core photonic bandgap fibers

Air-core photonic bandgap fibers offer many unique properties and are critical to many emerging applications. A notable property is the high nonlinear threshold which provides a foundation for applications at high peak powers. The strong interaction of light and air is also essential for a number of emerging applications, especially those based on nonlinear interactions and spectroscopy. For many of those applications, much wider transmission bandwidths are desired to accommodate a wider tuning range or the large number of optical wavelengths involved. Presently, air-core photonic bandgap fibers have a cladding of hexagonal lattice. The densely packed geometry of hexagonal stacking does not allow large nodes in the cladding, which would provide a further increase of photonic bandgaps. On the other hand, a photonic cladding with a square lattice can potentially provide much larger nodes and consequently wider bandgap. In this work, the potentials of much wider bandgap with square lattice cladding is theoretically studied and experimentally demonstrated.     

s-Shaped Software Reliability Growth Models and Their Applications

The s-shaped growth curves of detected software errors can be observed in software testing. The delayed s-shaped and inflection s-shaped software reliability growth models based on a nonhomogeneous Poisson process are discussed. The software reliability growth types of the models are investigated in terms of the error detection rate per error. In addition, a viable method for the software quality assessment, which integrates the capture-recapture method and the models above, is discussed, and its application to actual test data is illustrated.     

Development of a new heterojunction structure (ACJ -HIT) and its application to polycrystalline silicon solar cells

A new solar cell structure named HIT (Heterojunction with Intrinsic Thin layer) has been developed based on new artificially constructed junction (ACJ) technology. In this structure a non-doped a-Si thin layer was inserted between the p(a-Si)/n(c-Si) heterojunction, improving the output characteristics and achieving a conversion efficiency of 18.1%. This structure was applied to cast polycrystalline silicon solar cells of a practical size. A high conversion efficeincy of 13.6% was obtained with a cell size of 10 cm × 10 cm using various technologies, including hydrogen plasma passivation.