Development and Application of Multiple‐Probe Scanning Probe Microscopes

In the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple‐probe scanning probe microscopes (MP‐SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP‐SPM is used not only for observing high‐resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double‐probe STM (DP‐STM) developed by the authors, which was subsequently modified to a triple‐probe STM (TP‐STM), has been used to measure the conductivities of one‐dimensional metal nanowires and carbon nanotubes and also two‐dimensional molecular films. A quadruple‐probe STM (QP‐STM) has also been developed and used to measure the conductivity of two‐dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple‐probe AFM (QP‐AFM) with four conductive tuning‐fork‐type self‐detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general‐purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP‐AFM. These developments and applications of MP‐SPMs are reviewed in this paper.     

Identification of a Molecular Target of a Novel Fungal Metabolite,Pyrrolizilactone, by Phenotypic Profiling Systems

In the course of screening our microbial metabolite fraction library, we identified a novel pyrrolizidinone compound, pyrrolizilactone. In this study, we report the identification and characterization of a molecular target for pyrrolizilactone by using two phenotypic profiling systems. Cell morphology‐based profiling analysis using an imaging cytometer (MorphoBase) classified pyrrolizilactone as a proteasome inhibitor. Consistently, proteome‐based profiling analysis using 2D difference gel electrophoresis (DIGE; ChemProteoBase) also demonstrated that pyrrolizilactone is associated with proteasome inhibition. On the basis of these predictions, we determined that pyrrolizilactone is a novel type of proteasome inhibitor inhibiting the trypsin‐like activity of the proteasome.     

Switching kinetics of a Cu2S-based gap-type atomic switch

The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu(2)S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu(2)S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.     

Recent Developments in Solid Oxide Fuel Cell Materials

Recent developments in solid oxide fuel cell (SOFC) materials and stacks have been reviewed mainly from the viewpoint of the materials chemistry associated with stack development. Firstly the general features of SOFCs are described to clarify the materials problems which need to be solved and the technology that needs to be developed. The main, characteristic features of conventional SOFC materials are described with the emphasis put on the materials problems associated with the respective materials. Then the materials problems associated with stack development are described for tubular stacks and for planar stacks with oxide interconnect and with metal interconnect. Finally, new materials, design and processing are discussed in relation to new applications of SOFCs. The emphasis is placed on the fact that these are new challenges and therefore a more fundamental strategy for materials and stack development should be constructed on the basis of the materials science and technology developed mainly for conventional materials.     

Destabilization of cubic-stabilized zirconia electrolyte induced by boron oxide under reducing atmosphere

The stability of yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) electrolytes against boron oxide was examined. Boron oxide was painted on the polished surface of YSZ and ScSZ and annealed at 1273 K for 100 h under wet hydrogen flowing condition. The X-ray diffractometry, scanning electron microscopy/energy dispersive X-ray analysis, and Raman studies revealed that formation of Y₂O₃ and Sc₂O₃ occurred on YSZ and ScSZ surfaces contacting the boron oxide, but rare earth borates were not observed. The surface of electrolytes around precipitated particles became rough and phase transformation was confirmed from the cubic to the tetragonal or the monoclinic phases due to stabilizer removal from cubic zirconia. It has been also verified that small amounts of zirconium and yttrium were transported from the electrolyte to the gas phase via boron component. This destabilization effect induced by boron oxide was more serious for ScSZ than for YSZ. A destabilization mechanism under wet hydrogen atmosphere is proposed based on pseudo ternary phase diagrams for the YO_1.5–BO_1.5–ZrO₂ system and the ScO_1.5–BO_1.5–ZrO₂ system and thermodynamic considerations.     

A solid electrolyte nanometer switch

We have investigated solid electrolyte switches that utilize electrochemical reactions (deposition and dissolution) of metallic ions. The switch turns off or on when a metallic bridge electrochemically forms or dissolves in the solid electrolyte. Each state is nonvolatile and the switching is repeatable up to 10⁵ cycles. The promising application is a programmable switch in a field programmable logic because of its small size (<30 nm) and low ON resistance (<100Ω). This paper discusses the electrical characteristics, operation principle, and applications of the solid electrolyte switch. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 68–73, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20542     

Synthetic speech in foreign language learning: an evaluation by learners

Can synthetic speech be utilized in foreign language learning as natural speech? In this paper, we evaluated synthetic speech from the viewpoint of learners in order to find out an answer. The results pointed out that learners do not recognize remarkable differences between synthetic voices and natural voices for the words with short vowels and long vowels when they try to understand the meanings of the sounds. The data explicates that synthetic voice utterances of sentences are easier to understand and more acceptable by learners compared to synthetic voice utterances of words. In addition, the ratings on both synthetic voices and natural voices strongly depend upon the learners’ listening comprehension abilities. We conclude that some synthetic speech with specific pronunciations of vowels may be suitable for listening materials and suggest that evaluating TTS systems by comparing synthetic speech with natural speech and building a lexical database of synthetic speech that closely approximates natural speech will be helpful for teachers to readily use many existing CALL tools.