Table of contents

It is shown that UV-excited porous Si (PS) exhibits an efficient visible photoluminescence (PL) at room temperature. The PS layers were formed by anodization of p-type and n-type single-crystal Si wafers in aqueous HF solutions. The peak wavelength of PL spectra depends on the anodization parameters including the resistivity and the conduction type of Si substrates. The PL spectra can be tuned to a higher energy side by either adjustment of the anodizing conditions or chemical etching after anodization. These remarkable results can be interpreted as a result of quantum size effects in PS.

High-concentration modulation doping of beryllium (Be) for GaInAs/InP quantum wells (QWs) was achieved by chemical beam epitaxy (CBE) up to 1×10¹⁹ cm^-3. The modulation-doped quantum well (MD-QW) structure showed strong photoluminescence intensity. Broad-contact separate-confinement-heterostructure (SCH) QW lasers were also fabricated to evaluate the quality of MD-QWs. The measured threshold current density was 1.5-2.0 kA/cm² for devices with 200 µm width and 200-1000 µm cavity length. High concentration and modulation doping for GaInAs/InP lasers was demonstrated.

High-electric-field electron transport in a-Si:H films has been investigated by means of time-of-flight (TOF) measurements. The drift mobility increased with increasing applied field at lower temperature (≤300 K), accompanied by a simultaneous increase in the dispersion parameter resulting in nondispersive transport. The mobility was much less field-dependent at higher temperature where the nondispersive transport was attained. The experimental results are consistently explained by taking account of the increase in electron temperature (hot electron) at higher field into the theory of dispersive transport.

Metallic tin diffusion into p-type hydrogenated amorphous silicon (a-Si:H) deposited on a flat or textured SnO₂/glass substrate has been dramatically reduced by introducing a photo-nitrided a-Si:H (5-Å-thick) diffusion barrier between photochemical vapor deposition (photo-CVD) a-Si:H and SnO₂, and the diffusion depth is about 30 Å from the a-Si:H/SnO₂ interface. It is also shown that the optical transmittance is significantly improved by employing a 5-Å-thick photo-nitrided barrier layer.

The ESR signal in a-Si_1-xGe_x:H alloy films after fast cooling from an elevated temperature was compared with that after slow cooling. The reversible thermally induced increase in the neutral dangling bond density of about 20% was observed at 250°C. The reversible thermally induced change in the dark conductivity (σ_d) was also observed by the same heat treatment as for the ESR measurement.

Epitaxial CuAlSe₂ film has been grown on the GaP(100) substrate by molecular beam epitaxy, and its optical and electrical properties have been characterized. The spectrum of optical reflectance suggests that the band gap of the film is about 2.7 eV, which agrees with that of the bulk material. The photoluminescence spectrum at 77 K showed no band edge emission, but only deep level-related emissions ranging from 520 nm to 870 nm. The CuAlSe₂ sample exhibits n-type conductivity with the resistivity of 0.02 Ω·cm, the carrier concentration of 4×10¹⁸ cm^-3 and the mobility of 60 cm²·V^-1·s^-1.

High-quality ZnSe films were successfully grown on GaAs (100) at low temperatures, 200°C or lower, by hydrogen radical-enhanced chemical vapor deposition (HRCVD). Defects were markedly eliminated by the following factors: selection of source materials, avoidance of ion bombardment, and suppression of formation of adducts by alternate gas supply.

Short-period superlattices of (GaP)_n(AlP)_n have been grown by metalorganic vapor phase epitaxy. X-ray diffraction measurements have confirmed the formation of the structures, where n ranges from 4 to 10. Low-temperature photoluminescence has shown characteristic emission peaks, which shift toward higher energies and tend to increase in intensity with decreasing n. These results, together with the band discontinuity between GaP and AlP which was estimated from that between GaP and Al_0.6Ga_0.4P, strongly indicate that the (GaP)_n(AlP)_n system forms the superlattices of a type-II band alignment.

The gas sensitivity of Schottky gated poly(3-alkylthiophene) field effect transistors has been reported. The source-drain currents have been strongly influenced by air, water and chloroform gases. A large increase in transconductance of the (field effect transistor) FET is observed in chloroform gas. This is explained by the increase of the mobility with diffusion of chloroform molecules into the poly(3-alkylthiophene) films.

Oriented sintered (Bi_0.75Pb_0.25)₂Sr₂Ca₂Cu₃O₁₀ pellets have been irradiated up to 2×10¹⁸/cm² with 3 MeV electrons at 370 K. By X-ray line broadening analyses, the amount of disordered portion in the c-axis direction increased by about 20% on irradiation of 2×10¹⁸/cm². The intensity of Ca LMM Auger electrons decreased with increasing irradiation. The transition temperature onset remained unchanged at 110.1 K by irradiation, while the transition temperature offset decreased from 101.2 K to 94.7 K at the maximum irradiation dose. The above observations have been explained by the formation of the disordered portion in the grain surface by electron irradiation, which results in the reduction of the superconducting grain connection.

Using fine powders prepared by a freeze-drying process of a nitrate solution, a YBa₂Cu₃O_7-x superconductor has been successfully formed in a ceramic plate. The other processes employed are two heat treatments, a flash decomposition of the freeze-dried nitrates and a subsequent calcination. It has been found that the formation of high-quality ceramics requires ∼10% of the Cu nitrate to be added to the stoichiometric nitrate solution as a starting material of the freeze-drying process. The ceramics thus obtained have the characteristics of a very dense structure with large grains and exhibit magnetic properties as a high T_c superconductor as good as those of a monocrystalline YBa₂Cu₃O_7-x.

We have measured the resistivity of the Ag-Bi₂Sr_1.8Ca_1.2Cu₂O_y composite system with Ag volume fraction p_Ag ranging from 0.00 to 1.00. We find, for the samples with p_Ag<0.6, that the addition of Ag slightly decreases the superconducting transition temperature of Bi₂Sr_1.8Ca_1.2Cu₂O_y. For the samples with p_Ag>0.6, no zero-resistivity state is observed. The variation of the room-temperature resistivity with p_Ag indicates a three-dimensional percolating Ag matrix occurring at p_Ag≈0.17.

A Bi_1.5Pb_0.5Sr₂Ca₂Cu₃O_10-y ceramic was sequentially irradiated with ⁶⁰Co γ-rays of 1.5 MR·h^-1 in dose rate up to a dose of about 50 MR at ambient temperature, and the electrical resistivity was measured as a function of temperature. The critical superconducting transition temperature of 103.4 K increased to 104.1 K at 20.25 MR, and then decreased at a rate of 2.0×10^-2 K/MR on further irradiation. Concurrently, the electrical resistivity at 300 K increased almost linearly with a rate of 0.1 µQ·m/MR in the dose range of about 2 to 20 MR, and the resistivity was little changed by the irradiation to about 37 MR.

The high-T_c YBa₂Cu₃O_7-x (123) superconductor has been synthesized through a decomposition of organic acid salts. T_c's of 92 K have been obtained after a relatively short sintering in the 123 specimen. Effects of silver addition and zirconium substitution on superconducting properties and structures were studied. The Ag addition and the Zr substitution appreciably enhances the J_c of sintered 123 specimen. The Ag addition decreases the optimum sintering temperature by about 50°C. The Zr substitution is found to significantly change the morphology of 123 grains.

Superconducting Ba₂YCu₃O_7-y/Ag composite films were prepared on yttria-stabilized zirconia substrates by the dipping-pyrolysis process. Metal naphthenates were used as starting materials. Homogeneous Ba-Y-Cu-Ag solutions with (Ag/BYCO) molar ratios of 0-1.0 were spin-coated onto the substrates and pyrolyzed at 500°C. Subsequently, these prefired films were heat-treated at 750°C under a low-oxygen partial pressure (=2×10^-4 atm) followed by higher-p(O₂) annealing. High superconducting transition temperatures, T_c,onset(s)'s and T_{c,zero$(r)'s, of 88 K-90 Kwereobtainedforthecompositefilmswith (Ag/BYCO) molarratiosof 0.1-0.5.}

Temperature-dependent irreversibility magnetic fields, H_irr(T) were measured for four samples of silver-sheathed Bi_1.8Pb_0.4Sr₂Ca_2.2Cu₃O_x tapes having 3 levels of zero-field, 77 K critical current density, J_co, in magnetic flux densities up to 30 T and in the temperature range from 33 to 90 K. The measurements were performed for two orientations of the tape plane, the plane parallel to the applied magnetic field direction and that perpendicular to the applied field. The measurements show that H_irr increases with J_co, implying that H_irr is strongly dependent on the morphology of the superconductors. H_irr was obtained at 27.9 T and 54.7 K for the sample with J_co=298 A/mm² at 77.3 K.

Superconductor-semiconductor-superconductor weak links with a normal layer of InSb thin film were fabricated. A large normal resistance of 16 Ω and a critical supercurrent of 50 µA were obtained at 4.2 K for a channel length of 0.19 µm between Nb electrodes. The normal resistance of 16 Ω is about 40 times as large as that of a junction with the normal layer of a Si bulk crystal.

A series of non-acicular particulate media with coercivity of up to 2150 Oe, residual magnetization of up to 50 emu/g and squareness ratio of up to 0.72 has been developed based on γ-Fe₂O₃, modified with Mn, Co and Zn. They were prepared by coprecipitation of Fe, Mn, Co, and Zn ions from an aqueous solution, using an organic alkali, such as triethylamine, to adjust the pH, followed by suitable annealings. The fine particle size of around 50 nm, strong magnetocrystalline anisotropy and annealed directional ordering are possible causes of high coercivity. These media are potential candidates for high density recording.

Inclination of recorded magnetization in an obliquely metal-evaporated (ME) tape is estimated by the Bitter pattern technique. Although the contrast of the Bitter pattern evolved in a magnetic field of various directions to the film plane is generally asymmetric with respect to recording transitions, it becomes symmetric only when that magnetic field is applied in a direction determined by the recorded magnetization. For the Co-Ni-O film recorded at 1.5 kFCl, the inclination of magnetization is estimated to be about 40°. It is also shown that this value of the inclination agrees well with the theory.

A Pr³⁺-doped superfluorescent fluoride fiber laser operating in the 1.3 µm band is reported. An output power of 0.166 mW is obtained. The peak wavelength of superfluorescence is 1.306 µm which corresponds well to the central wavelength of optical telecommunication trunk line systems.

We have performed experiments on thin (6 µm) spray-deposited CdS films. All-optical and optoelectronic (hybrid) bistabilities were observed at 210 K. We have been successful for the first time in demonstrating that it is possible to reach, in thin CdS films, the same contrasted bistable loops in both transmission and photocurrent. The origin of the bistability is explained by the measured dependence of transmission on temperature. A generalized model based mainly on Urbach's rule is presented for calculating the temperature dependence of transmission. A good agreement between theory and measurement is obtained.

A new discovery is the illusion of 3-D transparent surface perception in the binocular fusion. When adequate visual stimuli are suitably arranged partially along the surface boundary or are given beyond the occluding illusory surface, a transparent or translucent illusory surface can be seen. These phenomena are unique to binocular fusion and have been classified into three categories: glassy (crystal) transparency, semi-transparency and translucent. Optogeometrical arrangements for the perception of these transparent illusory surfaces were clarified. The transparency of these surface has been investigated by using illusory probe stimuli. These newly found illusory phenomena have a close relationship to the visual perception of the 3-D structure of space in binocular viewing and can offer a clue by which to reveal the mechanism underlying the 3-D space perceiving ability of the human visual system.

An enhancement of interface states of Si MOS diode by gold diffusion is observed by the isothermal capacitance transient spectroscopy (ICTS) measurement. The observed ICTS spectra are identified as the interface states with the help of numerical simulation. Although the gold diffusion is accompanied by thermal annealing, the effect of the thermal annealing on the interface states is eliminated with the use of an extra annealing at a low temperature in a nitrogen ambient. It is also ascertained that the interface states enhanced by the gold diffusion increase as the density of diffused gold increases.

Electrically controlled birefringence (ECB) mode displays using liquid crystal with negative dielectric anisotropy are promising for highly multiplexed dot-matrix liquid-crystal displays. This mode, however, has the problem of a narrow viewing angle because it is based on the birefringence of the liquid-crystal molecule. To solve this problem, a double-layer electrically controlled birefringence (D-ECB) liquid-crystal display is proposed. In this device, each layer compensates the variation of retardation as a function of viewing angle. As a result, the liquid-crystal display with a wide-viewing-angle cone under the application of voltage was realized.

The trans and cis isomers derived from chiral 1-trifluoromethyl-3-phenyl-2-propen-1-ol were prepared as chiral dopants of ferroelectric liquid crystals. They were doped to an achiral compound possessing a smectic C phase, and the induced spontaneous polarization of the mixtures was investigated. The observed spontaneous polarization for the trans isomer is larger than that for the cis isomer. The signs and values of spontaneous polarization were explained by a model which examined the fitness of two typical conformers possessing positive and negative spontaneous polarization to the zigzag conformation of molecules in the smectic C phase.

Crystal structure analyses of new compounds, Cu₆O₈Cu₂X (X=Cl, NO₃), have been carried out using the X-ray powder pattern fitting method (Rietveld method) together with thermal analyses. Although these compounds have a face-centered cubic structure analogous to that of Cu₆O₈InCl previously reported with a space group of Fmm, the Cu₂ (24e site) ions have a quite different configuration from that of the corresponding In ion. From the results of the above-mentioned analyses together with chemical analyses, the compositions of these samples were obtained as Cu_5.7O₈Cu_1.9Cl_0.69(NO₃)_0.31 and Cu_5.7O₈Cu_1.9NO₃, respectively. The unit cell parameters are a=9.376(1) Å for the former and 9.481(1) Å for the latter. These compounds decompose to CuO at 400°C and 350°C, respectively.

We have confirmed that photorefractive Bi₁₂TiO₂₀(BTO) crystal has incongruent melting properties and the upper limit for growing BTO single crystals is found to be 11 mol% TiO₂. BTO single crystals 20 mm in diameter and 30 mm in length are successfully grown from a Bi₂O₃-rich melt by the Czochralski method. These crystals are light brown in color and transparent in the range over the absorption edge, near 450 nm. Growth rates of less than 0.5 mm/h prevent the grown crystal from excess Bi₂O₃ as inclusions. Facet and core characteristics are found to be dependent on the growth directions.

Here we show a new method of digital image analysis for determining the time sequence of nucleation directly from a final pattern divided by spherulites. Since the growth rate of spherulite with dense-branching morphology is generally constant, the space-time relation is extremely simplified. The information on the time event is completely contained in the spatial characteristics of the pattern (the centers and boundaries of spherulites). We describe a simple algorithm for calculating the nucleation time sequence and its application to polymer spherulites. The method can be widely applied to the pattern divided by spherulites of any material.

Aluminum nitride films were grown on the surface of the fluorozirconate glass by an ion-assisted deposition (IAD) method. The films did not affect the infrared transmission of the glass. The Al-N bonding in the films was confirmed by the IR absorption band centered around 650 cm^-1. The absorption decreased with assist ion beam current, which is attributed to the reduction of film thickness by the sputtering effect and agrees well in trend with the changes in visible transmission and thickness. The glass surface with the films exhibits good resistance to himidity.

The influence of water vapour on the SiO₂ growth rate in plasma oxidation is investigated. The oxygen plasma was generated by the rf power of 130 W in a parallel resonant condition, and the water concentration in the plasma was controlled by mixing a small amount of water vapour with dry oxygen gas through a bubbler device. It is found that the water vapour in oxygen plasma considerably enhances the SiO₂ growth rate. The refractive index of the SiO₂ film is not affected by the hydrogen partial pressure in the plasma.

The optical reflectivity of a GaAs wafer is found to decrease from about 45% down to about 5% for both the g-line and i-line by oxidation in low-power oxygen plasma at 300°C for 4 hours. The oxide layer on the GaAs top surface used as an in situ antireflection layer for optical microlithography is demonstrated to be effective.

A new thin-film cold cathode (TFCC), which is composed of a Sn-doped In₂O₃/Ta₂O₅/ZnS/Au, has been investigated. The TFCC, which is different from the cold cathodes reported so far, causes electron emissions by electrons flowing across the ZnS layer by a high ac-field. An average emission current of 28 nA/cm² has been obtained. To demonstrate the electron emission from the TFCC, cathodeluminescence from phosphor coated on an anode has been observed. The mechanism of the TFCC is also discussed.

Neutral ⁷Li and ⁶Li atoms are laser cooled and trapped using the 2²P_3/2(F=3)↔2²S_1/2(F=2) and 2²P_3/2(F=5/2)↔2²S_1/2(F=3/2) transitions, respectively. The Zeeman tuning is employed in the deceleration stage. Using a magneto-optical trap with a tetrahedral laser-beam configuration the atomic density of 3×10⁹ atoms/cm³ is obtained for ⁷Li and a half of that for ⁶Li. The measured temperature of the trapped ⁷Li atoms is 350±40 µK when the detuning is 8 MHz to the red.

The effects of a water treatment of the LaF₃ single crystal on an LaF₃-based oxygen sensor were investigated. It was found that the oxygen-sensing properties were significantly affected by the water treatment depending on the perovskite-type oxides (LaCrO₃, LaCoO₃, La_0.8Ca_0.2MnO₃) used as the sensing electrode material and the duration of the treatment. As revealed by XPS, the treatment induced the incorporation of oxygen in the surface region of the LaF₃ crystal, leading to an increase in the number of electrons of the electrochemical reduction of oxygen from 1 or 2 to 4.

Ion energy distribution is influenced by the magnetic field profiles in electron cyclotron resonance (ECR) plasma. When a 875 G equi-magnetic field is nonuniform, the microwave absorption concentrates at the ECR position which is located near the microwave window. Then, the mean ion energy distribution on the substrate holder becomes much broader due to the ion acceleration by the plasma potential difference. In addition, the ion energy distribution depends on the uniformity of the magnetic field gradient at the ECR position. The microwave is absorbed efficiently around the small gradient ECR position. Therefore, a uniform magnetic field gradient at the ECR position causes a uniform and sharp ion energy distribution.

X-ray diffraction study shows that an etching solution of 3% HF and 5% HNO₃ is the most suitable solution for preparing a bioactive surface layer of HA-glass-titanium composite, since the glass is removed, a great number of HA particles are exposed, and little CaF₂ is produced by the etching. Anodic polarization measurement demonstrates that the 3-min etching gives an electrochemically active surface of the composites. These results and SEM observations suggest that this solution provides an adequate surface of the composite for the dental and medical implants.