Generation of radially polarized Ti:sapphire laser beam using a c-cut crystal

First, it is demonstrated that with a c-cut Ti:sapphire crystal the generation of a nonpolarized laser beam is possible, in contrast to the conventional a-cut Ti:sapphire crystal, which produces a linearly polarized beam. Second, the generation of a radially polarized Ti:sapphire laser beam is demonstrated in combination with a c-cut YVO(4) crystal used as a selector of radial polarization.     

Nitric acid method for fabrication of gate oxides in TFT

We have developed low temperature formation methods of SiO₂ layers which are applicable to gate oxide layers in thin film transistors (TFT) by use of nitric acid (HNO₃). Thick (>10 nm) SiO₂ layers with good thickness uniformity (i.e., ±4%) can be formed on 32 cm × 40 cm substrates by the two-step nitric acid oxidation method in which initial and subsequent oxidation is performed using 40 and 68 wt% (azeotropic mixture) HNO₃ aqueous solutions, respectively. The nitric acid oxidation of polycrystalline Si (poly-Si) thin films greatly decreases the height of ridge structure present on the poly-Si surfaces. When poly-Si thin films on 32 cm × 40 cm glass substrates are oxidized at azeotropic point (i.e., 68 wt% HNO₃ aqueous solutions at 121 °C), ultrathin (i.e., 1.1 nm) SiO₂ layers with a good thickness uniformity (±0.05 nm) are formed on the poly-Si surfaces. When SiO₂/Si structure fabricated using plasma-enhanced chemical vapor deposition is immersed in 68 wt% HNO₃, oxide fixed charge density is greatly decreased, and interface states are eliminated. The fixed charge density is further decreased by heat treatments at 200 °C, and consequently, capacitance-voltage characteristics which are as good as those of thermal SiO₂/Si structure are achieved.     

Si cleaning method without surface morphology change by cyanide solutions

Hydrogen cyanide (HCN) aqueous solutions can remove copper contaminants from Si surfaces more effectively than hydrochloric acid/hydrogen peroxide mixture (HPM) and sulfuric acid/hydrogen peroxide mixture (SPM). When pH of the HCN solutions is adjusted at 9, Si surface morphology is not changed, while when pH exceeds 10, the Si surfaces are considerably roughed. AFM measurements show that Cu contaminants are present in the form of particles on the bare Si surfaces. XPS measurements show that the particles consist of metallic Cu. The Cu particle height decreases almost linearly with the cleaning time, and the Cu surface concentration decreases exponentially with it. It is concluded that Cu particles gradually dissolve into the HCN aqueous solutions by the direct reaction with cyanide ions at the surface of the Cu particles.     

Novel ordering of an S = 1/2 quasi-1d Ising-like antiferromagnet in magnetic field

High-field specific heat measurements on BaCo(2)V(2)O(8), which is a good realization of an S=1/2 quasi-one-dimensional (1D) Ising-like antifferomagnet, have been performed in magnetic fields up to 12 T along the chain and at temperature down to 200 mK. We have found a new magnetic ordered state in the field-induced phase above H(c) approximately 3.9 T. We suggest that a novel type of the incommensurate order, which is caused by the quantum effect inherent in the S=1/2 quasi-1D Ising-like antiferromagnet, appears in the field-induced phase.     

Tritium isotope separation by CO2-laser irradiation at low temperatures

Tritium isotope separation by CO₂-laser induced multiphoton dissociation of CTF₃ is investigated. For the optimization of the performance of this working substance, trifluoromethane, the conditions to yield high-selectivity at high-operating pressure and low-critical fluence for complete dissociation are studied using our deconvolution procedure. The irradiation conditions are varied over the following ranges; wavenumber: 1052–1087 cm^–1, gas temperature: 25°C to –78°C, CHF₃ pressure: 5–205 Torr. The selectivities exceeding 10⁴ are observed for 85–205 Torr CHF₃ at –78°C by the irradiation at 1057 cm^–1.     

Measurement of thermal diffusivity of filler-polymide composites by flash radiometry

Thermal diffusivity D of filler-polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminium nitride, silicon carbide, and silicon carbide whiskers, Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape on D were studied. D increased with increasing average filler particle diameter and filler content. For the composite filled with fine Al₂O₃ whose average particle diameter is about 0.2 μm, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AIN, there was a strong increase in D above a filler content of 20 vol %. D was ten times larger than that of unfilled polyimide when the BN content was 54 vol %. D of the SiC-whisker composite increased strongly up to a filler content of 18 vol %. Above this content D significantly decreased, probably because of interconnected voids formed by mold shrinkage.     

A sphere can be characterized as a smooth ovaloid which contains one circle through each point

A sphere inE ³ can be characterized as a smooth ovaloid which contains one circle of an arbitrary but fixed radius through each point.Dedicated to Professor N. K. Stiphanidis on his 65th birthday     

Effects of excess oxygen content on the hole-carrying CuO2-layers in Tl2(Ba1−xSrx)2Ca2Cu3Oy superconducting oxides

The effects of oxygen doping on the hole-carrying CuO₂-layers in Tl₂(Ba_1−xSr_x)₂Ca₂Cu₃O_y were studied by combined chemical and valence analysis, T_c measurements and neutron diffraction. The highest T_c is characterized by an optimal excess oxygen content, Δy, dichotomizing the under- and over-doped regions for each Sr concentration. While the average Tl valence is close to 3.0 and independent of Δy, the average Cu valence shows a linear dependence with Δy. An increase of the flatness of the CuO₂ plane, characterized by the O(2)-Cu(2)-O(2) bond angle of ∼176°, was observed at the optimal Δy.     

Isotope effect in the diffusion of hydrogen and deuterium in polymers

Temperature dependences of diffusion and permeation coefficients of hydrogen and deuterium in glassy and rubbery polymer films have been measured. The size of the free volume element in rubbery polymers has been calculated according to the theory of Frisch and Rogers for the quantum isotope effect, but the free volume is too large for precise calculation below the glass-transition temperature. The cooperative movement of segments is also discussed using the ratio of preexponential factors for diffusion mechanisms above and below the glass-transition temperature.     

An adaptive correlation ratemeter: a new method for Doppler fetal heart rate measurements

For use in a cardiotocograph, ultrasound Doppler fetal signals have been thought to provide merely a limited reliability of the fetal heart rate record because of the difficulty of signal processing to obtain a consistent trigger, although the signal itself is easy to obtain with an excellent signal-to-noise ratio.However, the authors have developed a unique signal processing system using a correlation technique with an automatic adaptation algorithm, which solved almost all of the difficulties associated with the old Doppler cardiotocograph and showed that the ultrasound Doppler fetal signal can also provide heart rate records compatible to that obtained by a fetal ECG system.The authors are sure that their method is a most promising one in the coming age of microprocessor-oriented instrumentation.