Frontier of transparent oxide semiconductors

Recent advancements of transparent oxide semiconductors (TOS) toward new frontiers of “oxide electronics” are reviewed based on our efforts, categorized as “novel functional materials”, “heteroepitaxial growth techniques”, and “device fabrications”. Topics focused in this paper are: (1) highly conductive ITO thin film with atomically flat surface, (2) p-type TOS material ZnRh₂O₄, (3) deep-ultraviolet (DUV) transparent conductive oxide β-Ga₂O₃ thin film, (4) electrochromic oxyfuolide NbO₂F, (5) single-crystalline films of InGaO₃(ZnO)_m grown by reactive solid-phase epitaxy, (6) p-type semiconductor LaCuOS/Se epitaxial films capable of emitting UV- and purple-light, (7) p–n homojunction based on bipolar CuInO₂, (8) transparent FET based on single-crystalline InGaO₃(ZnO)₅ films, and (9) UV-light emitting diode based on p–n heterojunction.     

Real-time video-based rendering from uncalibrated cameras using plane-sweep algorithm

In this paper, we present a new online video-based rendering (VBR) method that creates new views of a scene from uncalibrated cameras. Our method does not require information about the cameras intrinsic parameters. For obtaining a geometrical relation among the cameras, we use projective grid space (PGS) which is 3D space defined by epipolar geometry between two basis cameras. The other cameras are registered to the same 3D space by trifocal tensors between these basis cameras. We simultaneously reconstruct and render novel view using our proposed plane-sweep algorithm in PGS. To achieve real-time performance, we implemented the proposed algorithm in graphics processing unit (GPU). We succeed to create novel view images in real-time from uncalibrated cameras and the results show the efficiency of our proposed method.     

Microstructure and enhanced morphology of planar nonpolar m-plane GaN grown by hydride vapor phase epitaxy

Nonpolar ( ) m-plane gallium nitride has been grown heteroepitaxially on (100) γ-LiAlO₂ by several groups. Previous attempts to grow m-plane GaN by hydride vapor phase epitaxy (HVPE) yielded films unsuitable for subsequent device regrowth because of the high densities of faceted voids intersecting the films’ free surfaces. We report here on the growth of planar m-plane GaN films on (100) γ-LiAlO₂ and elimination of bulk and surface defects. The morphology achieved is smooth enough to allow for fabrication of m-plane GaN templates and free-standing substrates for nonpolar device regrowth. The GaN films were grown in a horizontal HVPE reactor at 860–890°C. Growth rates ranged from 30 μm/h to 240 μm/h, yielding free-standing films up to 250-μm thickness. The m-plane GaN films were optically specular and mirror-like, with undulations having 50–200-nm peak-to-valley heights over millimeter length scales. Atomic force microscopy revealed a striated surface morphology, similar to that observed in m-plane GaN films grown by molecular beam epitaxy (MBE). Root-mean-square (RMS) roughness was 0.636 nm over 25-μm² areas. Transmission electron microscopy (TEM) was performed on the m-plane GaN films to quantify microstructural defect densities. Basal-plane stacking faults of 1×10⁵ cm⁻¹ were observed, while 4×10⁹ cm⁻² threading dislocations were observed in the g=0002 diffraction condition.     

Preparation of Monolithic Porous Titania-Silica Ceramics

Monolithic porous ceramics composed of TiO₂ (67 mol%) and SiO₂ (33 mol%) were prepared via casting a melt in the Na₂O-CaO-TiO₂-P₂O₅-SiO₂ system and subsequent acid leaching of the resultant ceramics which are constituted of NaCaPO₄, TiO₂, and amorphous SiO₂. The median pore diameter and specific surface area of the resulting porous ceramics are approximately 1 μm and 40 m², respectively. Amorphous silica surrounds the submicrometer-sized particles of TiO₂ acting as a binder and retaining monolithic forms. No significant shrinkage in the pore size occurred upon heating up to 1000°C.     

Investigation of Lithium Diffusion in Octalithium Plumbate by Conductivity and NMR Measurements

Diffusion of lithium ion and tritium in octalithium plumbate (Li_sPbO₆) was studied. The electrical conductivity of the polycrystalline pellets measured by the two-terminal ac method in the temperature range of 300 to 973 K was one of the highest among oxide lithium ceramics. The temperature dependence of the conductivity is consistent with the nuclear magnetic resonance of lithium-7 powder samples, suggesting that the temperature dependence of the diffusion of lithium consists of three regions in this temperature range. Preliminary measurements of the diffusion coefficient of tritium in neutron-irradiated Li_sPbO₆ powder were also carried out. The results were compared with the diffusion of lithium ion, and the relationship between diffusion of lithium ion and tritium is discussed.     

Secure optical memory system with polarization encryption

A novel secure holographic memory system with polarization encoding is proposed. Two-dimensional original data are encoded as a two-dimensional polarization distribution. The polarization state at each pixel is scrambled by a mask that changes the polarization state into a random state. The mask can rotate the direction of the principal axes of the elliptically polarized light and can change the phase retardation at each pixel. The light with the random polarization state is stored as a hologram that can produce the vector phase-conjugate beam. In the decryption the vector phase-conjugation readout can recover the original polarization state by use of the same mask used in the encryption. Experimental results of encryption and decryption with a bacteriorhodopsin film are presented.     

Space development, SPS 2000, and economic growth: the need for macro-engineering diplomacy

Solar power generation in space is anticipated as one remedy toward the solution of global environmental problems, including the energy crisis. It is argued that several problems could be solved through global cooperation that makes practical use of space solar power. Such applications today require the reduction of space transportation costs to one-hundredth or less, and the satisfactory operation of a viable pilot plant. In turn, this means that macro-engineering diplomacy is indispensable. The role that the Japanese Ministry of International Trade and Industry (MITI now METI, Ministry of Economy, Trade and Industry) would be expected to play in the former, and the proposal for an SPS 2000 pilot plant project for the latter, are discussed in this paper. Like the U.S. Federal Aviation Administration (FAA), MITI should promote the reduction of space transportation costs by encouraging the private sector to create new industries and grow the economy. An Equatorial Alliance, formed by the equatorial countries that would be supplied with space solar power by SPS 2000, could take the lead in solving global warming problems.     

A Low-Noise Terahertz SIS Mixer Incorporating a Waveguide Directional Coupler for LO Injection

We have developed a low-noise heterodyne waveguide Superconductor-Insulator-Superconductor (SIS) mixer with a novel local oscillator (LO) injection scheme for the Atacama Large Millimeter/submillimeter Array (ALMA) band 10, over the frequency range 0.78–0.95 THz. The SIS mixer uses radio frequency (RF) and LO receiving horns separately and a waveguide 10 dB LO coupler integrated in the mixer block. The insertion loss of the waveguide and coupling factor of the coupler were evaluated at terahertz frequencies at both room and cryogenic temperatures. The double-sideband (DSB) receiver noise temperatures were below 330 K (7.5hf/k _B) at LO frequencies in the range 0.801–0.945 THz. The minimum temperature was 221 K at 0.873 THz over the intermediate frequency range of 4–12 GHz at an operating temperature of 4 K. This waveguide heterodyne SIS mixer exhibits great potential for practical applications, such as high-frequency receivers of the ALMA.     

Formation Mechanism of Fullerene Cation in Bulk Heterojunction Polymer Solar Cells

The charge carrier dynamics in blend films of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) and conjugated polymers with different ionization potentials are measured using transient absorption spectroscopy to study the formation mechanism of PCBM radical cation, which was previously discovered for blend films of poly[2‐methoxy‐5‐(3,7‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV) and PCBM. On a nanosecond time scale after photoexcitation, polymer hole polaron and PCBM radical anion are observed but no PCBM radical cation is found in the blends. Subsequently, the fraction of polymer hole polarons decreases and that of PCBM radical cations increases with time. Finally, the fraction of PCBM radical cations becomes constant on a microsecond time scale. The final fraction of PCBM radical cation is dependent on the ionization potential of polymers but independent of the excitation wavelength. These findings show that the formation of PCBM radical cation is due to hole injection from polymer to PCBM domains. Furthermore, the energetic conditions for such hole injection in polymer/PCBM blend films are discussed on the basis of Monte Carlo analysis for hole hopping in a disordered donor/acceptor heterojunction with varying energetic parameters.     

Application of 10-microm thin stainless foil to a new assembly of the specimen carrier in high-pressure freezing

High-pressure freezing (HPF) has been accepted generally as the most reliable method for cryoimmobilization of biological samples. However, the depth of vitreous freezing in biological samples was less than expected, probably because of the poor thermal conductivity with high water contents. In this study, we introduce a new assembly of the specimen carrier using a 10-microm thin stainless foil for the specimen chamber cover in the HPF technique and describe the fine structure of rat gastric glands processed with the assembly. A low-magnification view of the gastric surface region showed a well-preserved morphology in which the vitreous freezing reached deeper than 100-microm from the freezing face. The present results prove that the 10-microm thin stainless foil is useful in HPF, providing deep vitrification in biological samples.