Yusuke Sakamoto

Fermi-Level Tuning of Topological Insulator Thin Films

Topological insulators are insulating materials but have metallic edge states with peculiar properties. They are considered to be promising for the development of future low energy consumption nano-electronic devices. However, there is a major problem: Naturally grown materials are not truly insulating owing to defects in their crystal structure. In the present study, we have examined the electronic structure and transport properties of topological insulator ultrathin Bi2Te3 films by angle-resolved photoemission spectroscopy and in situ transport measurements. To realize a truly bulk insulating film, we tried to tune the Fermi-level position using two methods. The first of these, i.e., changing the Si substrate temperature during film growth (350?450 K) to reduce the defects in the grown films, had some effect in reducing the bulk residual carriers, but we could not fabricate a film that showed only the surface states crossing the Fermi level. The second method we employed was to incorporate Pb atoms during film growth since Pb has one less electron than Bi. When the films were grown at around 350 K, we observed a systematic shift in the Fermi level and obtained a bulk insulating film, although it was not possible to move the Dirac point just at the Fermi level. The change in the measured film conductivity was consistent with the shift in the Fermi level and suggested the detection of the surface-state conductivity. For films grown at a higher substrate temperature (450 K), the Fermi level could be tuned only slightly and a bulk n-type film was obtained. Pb incorporation changes the shape of the Dirac cone, suggesting the formation of a stoichiometric ternary alloy of Bi, Pb, and Te, which is another topological insulator.

2110 Effects of SOFC Electrode Microstructure on Polarization Characteristics

Anode microstructure parameters were quantified by SEM-EDX measurements and the dependence of polarization characteristics on the anode microstructure parameters is investigated experimentally. Anode microstructure was successfully imaged and quantified by ultra low voltage SEM and by means of stereology. Cell voltage measurements and impedance spectroscopy were performed at 650 and 750 ̊C with hydrogen diluted by nitrogen as a fuel. A quantitative relationship between measured polarization and microstructure parameters, e.g., three phase boundary length, contiguity, etc., was discussed. Finally, a cell with an anode functional layer (AFL) was fabricated to investigate the possibility of improving both activation and concentration polarization characteristics.

Application of Content-Based Network for Sensor Data Distribution System

This paper proposes and evaluates a new sensor data distribution system, based on the content based network technology. This system is an overlay XML-based content-based routing system over the plain unicast IP network. As the application of the prototype system, we have selected Live E! project, whose object is collecting the weather information from various weather stations and distributing these digital data to the appropriate receiver nodes using the XML-based content-based multicast service. We have designed (1) the representation format of sensor information with XML, (2) content-based multicast routing algorithm using XPath. We have implemented the proposed system for its technical and functional validation

Remote Sensing of Neutral Particles in Upper Atmosphere Using Artificial Ion Beam

[Abstract] This paper describe that the instrumental improvement for application of the ECR Ion thruster to upper atmosphere observation system. It is developed the study of remote sensing method of neutral particles in the upper atmosphere using artificial energetic neutral atoms (ENAs) in the laboratory. It is generally known that atomic oxygen is dominant neutral gas in the upper atmosphere 200km and 700km altitude. And we need to estimate the atomic oxygen density by krypton ion beam in the laboratory. We studied the atomic oxygen source for ground experimental demonstration.