Measurement of surface recombination velocity of silicon wafers under sunlight condition by novel photoluminescence surface state spectroscopy

For a successful realization of super-high efficiency solar cells, reduction of surface or interface recombination is required. Thus, it is important to know the value of the surface recombination velocity (S) for the optimization of the passivation technology and for the design of solar cells. In this paper, a photoluminescence (PL) based novel technique for the measurement of the value of S under sunlight is presented, and applied to variously passivated Si surfaces. S was found not to be constant but to depend strongly on the excitation intensity near and above 1 sun condition. The value of S is strongly reduced under concentrated sunlight indicating that concentration of sunlight or use of a thin film is effective for efficiency increase.     

A fission yeast gene encoding a protein that preferentially associates with curved DNA

We searched for fission yeast (Schizosaccharomyces pombe) proteins that preferentially bind to a synthetic curved DNA sequence, by means of a DNA-binding gel shift assay in the presence of an excess amount of a non-curved DNA sequence as a competitor. We identified such a protein in S. pombe. The protein, thus purified, has an apparent molecular weight of 42 000, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was suggested that this protein (42 K-protein) recognizes and binds to a curved DNA structure in a given nucleotide sequence, although it also binds to a non-curved DNA sequence with lower affinity. As its putative coding sequence, a 1·9-kilobase genomic DNA from S. pombe was cloned and sequenced. Sequencing of a cDNA clone also revealed the existence of an open reading frame, with no intron, encoding a 381-amino-acid protein with a calculated molecular mass, 41 597. This protein appears to be located in the nucleus. The predicted protein sequence revealed that the 42 K-protein exhibits no significant similarity to any other known proteins, except to a hypothetical protein of Caenorhabditis elegans.     

Reliability and early failure in Cu/oxide dual-damascene interconnects

Recent results on up-direction electromigration (EM) studies on Cu dual-damascene (DD) interconnects are presented. The issue of the DD process and its potential effect on EM reliability is described with special focus on the peculiarities of the DD interconnect architecture in comparison to the previous subtractively etched Al-based interconnect technology. Experiments performed on multilink, DD interconnects that highlight EM reliability issues, such as early failure, and the Blech effect are summarized.     

Synthesis and photoelectrochemical characterization of (Ag2S)x(In2S3)1−x and AgInS2−ySey

Ternary n-type AgInS₂ and AgIn₅S₅ have been synthesized selectively by homogeneous precipitation from an aqueous solution containing the prescribed amounts of AgNO₃, In₂(SO₄)₃, Na₂S₂O₃ and CH₃COOH followed by heat treatments of the resulting precipitates at 500–800°C. Quaternary n-type AgInS_2−ySe_y semiconductors were also synthesized by sintering of a mixture of as-precipitated AgInS₂ and elemental Se. Photoelectrochemical characterization of these semiconductors was studied using the photoanodes prepared in the form of sintered pellets in a polysulfide electrolyte. Compared with the relatively poor saturated photocurrent for AgInS₂ (0.7 mA/cm²) and AgIn₅S₈ (0.01 mA/cm², AgInS_1.5Se_0.5 photoanode exhibits a higher photocurrent (20 mA/cm²) under 100 mW/cm² white-light illumination. This effect has been ascribed to the development of a highly oriented chalcopyrite crsytal during the sintering process at 800°C for 2 h. The chalcopyrite is a solid solution of AgInS₂ and AgInSe₂ and has band gaps between those of AgInS₂ and AgInSe₂. An energy conversion efficiency of 0.55%, a fill factor of 0.40, and a V_oc of 0.23 V has been obtained for the oriented quarternary photoanode.     

Ordering and organization in ionic solutions and emulsions

Recent studies on ionic distribution in solutions and in suspensions were reviewed. Suspensions of latex particles, which were large enough to be seen under an ultramicroscope, were investigated by the 2-D Fourier transformation. The micrograph showing ordered structures gave discrete scattering spots, whereas those of disordered arrangements displayed no spots or halos. The two-state structure gave a limited number of halo, confirming our previous conclusion that the very frequently observed single, broad scattering peak was reminiscent of some kind of ordering of solute species. By using an image data analyser, the crystallization process was shown to follow the Ostwald ripening mechanism. The concurrent study by the quasi elastic light scattering method and by the Fourier analysis gave consistent scattering profiles, which indicated that the ordering phenomena took place in the entire volume of suspensions. The scattering intensity (correctly the lattice factor) was calculated for cubic systems with paracrystalline distortion. The peak intensity was lowered by enhanced distortion, while the peak position itself was not affected. This justifies our previous treatment of the single, broad peak in terms of the Bragg equation. The experimentally found scattering curve was compared with this theoretical calculation; the degree of distortion was evaluated.     

Thermal decomposition of additive polymerization initiators. I. Azobisisobutyronitrile

We measured the rate of thermal decomposition of azobisisobutyronitrile (AIBN) from the rate of loss of 2,2-diphenylpicrylhydrazyl (DPPH) on reaction of the free radicals formed by thermal decomposition of azobisisobutyronitrile (AIBN) in organic solvents with DPPH. There has been some doubt about the quantitative relation between AIBN and DPPH required to get the rate constant of thermal decomposition of AIBN. In the past, AIBN has been used in excess, and the rate constants measured by using DPPH are smaller than they ought to be. In our experiments we used as little of AIBN relative to DPPH as possible and obtained a value of 3.8 × 10^?4 min.^?1 at 50°C. as the rate constant of the first-order reaction, which was shown satisfactorily by the linearity of the graph. We also obtained 32 kcal./mole as activation energy. We were also able to make clear the meaning of the result when a large quantity of AIBN was used.     

Fiber making directly from poly(tetrafluoroethylene) emulsion

Poly(tetrafluoroethylene) (PTFE) fiber with a superior mechanical property was prepared directly from its emulsion by the novel manufacturing process. The PTFE emulsion turned into a paste when a high shear flow was applied and the paste was extruded through a nozzle into a strand consisting of fine PTFE particles. The diameter of the strand was reduced stepwise by applying the die-drawing process through a conical die at a low temperature. The strand was further die-drawn down at elevated temperatures into fine PTFE fibers with a highly oriented crystalline structure. The crystalline orientation factor of the PTFE fiber reached very close to unity. Although the fibers obtained have a very high tensile modulus, the tensile strength was not as high as that expected from the crystalline orientation, suggesting that the presence of some defects in the PTFE fiber formed in the instantaneous deformation.     

Crystal structure of GeTe and Ge2Sb2Te5 meta-stable phase

Direct X-ray diffraction measurement of the erased state of the Ge–Sb–Te recording layer in a four-layered phase change optical disk, which was produced by an optical disk drive, was performed. It was identified as an fcc crystal structure. In order to carry out the detailed crystal structure analysis by the powder X-ray diffraction method with Rietveld refinements, somewhat larger amount of the fcc crystal powder was prepared from deposited 10 μm thick films. It revealed that Ge₂Sb₂Te₅ belongs to the NaCl type structure (Fm m) with the 4a site including 20% vacancies. The conclusion was supported by the results of the density measurements with Grazing Incidence of X-ray Reflectivity.     

Preparation of chiral poly(diacetylene) films from 10,12-pentacosadiynoic acid using circularly polarized light

By irradiating evaporated 10,12-pentacosadiynoic acid (p-DA) monomer film with circularly polarized light (CPL), we prepared chiral poly(diacetylene) [PDA] film. The circular dichroism (CD) was obtained reproducibly, depending on the rotational direction of the CPL. The induced chirality showed the dependence on the substrate temperature used for the preparation of evaporated p-DA monomer films, and it was stable after the transition to red-phase by annealing. Results suggest that side chain of polymer made a significant contribution to the formation of red-phase chiral PDA.