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Research Results
2010 | 2009 | 2008 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 | 1999 |
Nov. 2007
 Electrical conductivity of lithium borohydride (LiBH4) jumped by three orders of magnitude due to structural transition from orthorhombic to hexagonal at 388 K. The electrical conductivity in the hexagonal phase (in the order of 10-3 Scm-1) is due to Li super-ionic conduction. This study, collaborated with Assoc. Profs. H. Takamura and H. Maekawa (Graduate School of Engineering, Tohoku University), will lead to the developments of advanced solid-state electrolytes for high-safety lithium ion battery. The result was published in Applied Physics Letters (91, 224103, 2007), and reported in Nikkei BP (online), Nikkan-Kougyo Shimbun, Kahoku Shimpo (November 30, 2007) and Nikkei-Sangyo Shimbun (December 7, 2007).  
Sept. 2007
  Theory of Solid State Physics group (Prof. Maekawa's group) has found, in collaboration with RIEC and JST, the drive mechanisms of magnetic domain wall motion induced by electrical currents and magnetic fields are fundamentally different, using the ferromagnetic semiconductor (Ga,Mn)As within the thermally activated subthreshold, or ``creep," regime. This finding conduces a new development of magnetism and accelerates the realization of nonvolatile magnetic random access memory (MRAM) using domain walls. This result was published in Science on September 21st (US eastern time), and also introduced in Nikkei Sangyo, Kikkan Kogyo, and Kagaku Kogyo on September 21st and in Kahoku Shimpo on October 1st.
Prof. Maekawa’s group (Theory of Solid State Physics)
Sept. 2007
  We clarified the formation mechanism of dendrite crystals from Si melt based on fundamental experiments using a newly developed in-situ observation system. The knowledge was successfully implemented to “dendritic casting method” for realization of Si multicrystals and wafers with controlled grain orientations, grain sizes, and grain boundary characters which have never been achieved before. The dendrite casting method permits to realize Si multicrystals with high-quality and high-uniformity, which is required for development of high-efficiency solar cells to accelerate long-term and global scale installation of solar cells.  It has been well known that more than two parallel twins exist at the center of a facetted dendrite. However, the underlying mechanisms have not been fully understood. We proposed a model to involve the formation of a twin boundary at the {111} facet plane, and confirmed its validity. Furthermore, we clarified relationship between the parallel twins and the nucleation of dendrite crystals, and quantified the critical amount of supercooling for the appearance of the dendrite crystals using in-situ observations.  Thanks to the fundamental understanding of the growth mechanisms, Si multicrystals with high-quality and high-uniformity have been successfully obtained by the dendritic casting method. Although the growth was performed in a small crucible compared with the industrial scale, the solar cell based on the Si multicrystal-wafers grown by the dendritic casting method exhibited conversion efficiency similar with those based on commercially available high-quality Si multicrystal-wafers, which have been independently confirmed by our industrial partner. This indicates the possibility that further up-scaling of the crucible size results in very high-quality Si multicrystals, which could be comparable with or surpass the quality of Si single crystal.  The results were presented at the European Photovoltaic Solar Energy Conference in Milano on 4 September, and were reported in the on-line news of Nikkei Microdevices on 6 September.
Prof. Nakajima’s group (Crystal Physics)
July. 2007
  Synthesis technique of aluminum hydride, as a high-density hydrogen storage material, was developed, under the collaboration with The Japan Steel Works, LTD.. Our group, together with Prof. C.M. Jensen group at Hawaii Univ., has succeeded in the synthesis and clarified fundamental hydrogen properties of typical three type aluminum hydrides . Based on the international collaboration, The Japan Steel Works has industrially developed the synthesis process of aluminum hydride (material-supply for users is planned). Compared hydrogen desorption tests of aluminum hydride and commercialized hydrogen storage materials on a portable fuel cell device, aluminum hydride could achieve approximately two times higher performance with a half weight than the commercialized ones. The results were reported in Kagaku-Kougyo Nippou, Tekkou Simbun (July 23, 2007), Nikkei-Sangyo Shimbun (July 24, 2007), and Nikkan-Kougyo Shimbun (July 30, 2007).
July. 2007
 Low Temperature Condensed State Physics group (Prof. Iwasa’s group) has fabricated single-walled carbon nanotube transistors on flexible plastic substrates in collaboration with Prof. M. Shiraishi (Osaka University) and Brother Industries, Ltd.. We succeeded in applying ink-jet process to nanotube transistors, which is suitable for large-area electronics, and in fabrication of transistors on any type of substrate, including flexible plastic substrates. This technique accelerates the realization of carbon nanotube flexible electronics. This result was introduced with Nikkei-Sangyo Shimbun on July 4 and July 17. 
Prof. Iwasa’s group (Low Temperature Condensed State Physics)
July. 2007
 The fabrication processes for vertical type-typ light-emitting diodes (LEDs) using metal buffer layers and chemical lift-off process were developed. These processes were applied to the fabrication of high-brightness blue LEDs. We succeeded in realizing high-brightness vertical-type blue LEDs. This is the first achievement in realizing vertical LEDs using the CLO process based on metal buffer. It is possible to make the n-contact area on the back side of vertical LEDs, so that the whole front side can emit light, which should give considerable advantage in fabricating high-brightness LEDs. This is not possible in the case of conventional LEDs, in which the n-contact are is fabricated on the front side. Besides, high power LEDs can be easily realized by wafer bonding technique of metal substrate with good thermal conductivity. This technique is suitable for mass production of vertical type high brightness and power blue LEDs. This result was introduced with Kahoku Shimpo (July 6). 
Prof. Yao’s group (Physics of Electronic Materials)
May. 2007
  We grew a novel compound of NpPd5Al2 single crystal and discovered the world’s first superconductivity of the neptunium compound. The superconducting transition temperature is 5 K, which is relatively high among the heavy fermion superconductors. The upper critical field where the superconductivity state is killed is a very large value of 15T, which is 500,000 times larger than the earth magnetism. Although the neptunium ion possesses the magnetism, the superconductivity emerges. Furthermore it is found that the unconventional superconductivity with anisotropic energy gap is realized. The results were reported in the top page of “Kahoku Shimpo” on May 26, “Nikkan Kogyo Shimbun” on May 28 and "Joyo Shimbun" on May 28. The paper, which was selected as a “Papers of Editor’s Choice”, was published in J. Phys. Soc. Jpn. This work has been done in collaboration with Japan Atomic Energy Agency and Osaka University.
Prof. Shiokawa’s group (Radiochemistry of Metals),
International Research Center for Nuclear Materials Science
Apr. 2007
  Professor Y. Furuya (Hirosaki University), Distinguished IMR Fellow/Project Leader A. Inoue (President of Tohoku University) and Associate Professor H. M. Kimura (IMR of Tohoku University) succeeded in development of an innovative “Rapid-Rotation Centrifugal Casting Process” which enables the reduction in costs of the components and commercial production of the amorphous bulk metallic glassy alloys (BMGs). Metallic glass pipes, small gears, screws and biomedical artificial dental root model were able to be produced successfully from Zr or Fe metallic glassy alloy systems within only a few seconds at one process by using this method, that is, the molten raw BMG alloys were poured into copper mold with rotation speed of 3,000 rpm which causes 80 times as much centrifugal pressurization force as gravity. Because of synergistic effect of rapid solidification and high pressurization casting in the innovative manufacturing process of metallic glass components, this process has many technical advantages such as expansion of element ingredient composition, uniformity of the quality, reduction of internal defects and prevention of degradation at the secondary fabrication process of BMGs, etc. It will be easy to apply this process to automation. As a result, mass production and great reduction in costs of metallic glass components will be possible in the very near future. The “Rapid-Rotation Centrifugal Casting” technology will attract great attention as a breakthrough for bulk metallic glass technology since the costs has been the biggest problem for metallic glasses to commercial utilization in comparison with the conventional materials. These results were presented at the Spring Meeting of Japan Institute of Metals 2007 on March 28, Chiba Institute of Technology, and were introduced with Kahoku Shimpo (March 24 morning newspaper), and Nikkan Kogyo Shimbun (March 27).
Mar. 2007
  Recently, Nojiri Group (IMR, Tohoku Univ.), Japan Atomic Energy Agency Group and other collaborators have developed techniques for high magnetic field synchrotron X-ray experiments beyond 50 T using very small pulsed-magnets. We have succeeded in observing valence states directly in a valence transition compound, YbInCu4 at very high magnetic fields for the first time. It should be noted that we could determine the valence without thermal excitation effects by performing the experiments at very low temperatures. This high-field X-ray absorption spectroscopy can be applied to other intriguing substances such as spintronics materials. Further development to more advanced spectroscopy, e.g., X-ray Magnetic Circular Dichroism (XMCD) is also expected.   This work was published in J. Phys. Soc. Jpn. 76 (2007) 034702 and also reported in a newspaper (Kagaku Shinbun, 2007.3.30).
Mar. 2007
  Magnetic Materials group (Prof. Takanashi’s group) has found, in collaboration with Prof. S. Imada, Osaka University, the thinnest limit for the perpendicular magnetization in FePt thin films at room temperature, using soft x-ray magnetic circular dichroism measurements in SPring-8/JASRI. FePt films keep perpendicular magnetization at room temperature even for the thickness down to 1 nm, but only at low temperature for the thicknesses smaller than 1 nm. FePt ordered alloy with large magnetic anisotropy, guaranteeing the thermal stability of magnetization on a nanometer scale, has attracted much attention for the application to ultra-high density magnetic storage devices. The understanding of the thinnest limit is important from a practical point of view. This result was published in Applied Physics Letters, and also introduced in Nikkan-Kogyo Shimbun (March 16) and Nikkei-Sangyo Shimbun (March 19).
Jan. 2007
  ZnO, a transparent oxide semiconductor, is of growing importance in advanced electronics. Epitaxial growth of ZnO has been the subject of intense focus leading to our recent demonstration of ultraviolet light-emitting diodes and transparent field-effect transistors. Here we have observed the quantum Hall-effect (QHE) in a high-mobility two-dimensional electron gas in ZnO based heterostructures. Demonstration of the QHE in an oxide heterostructure presents broad possibilities not only to realize transparent electronics but also to combine QHE with the versatile functionality of oxides in complex heterostructures. The work was done in collaboration with RIEC and JST, and was published in Science (online express) on January 25th (US eastern time). The highlights on our work was reported in newspapers (Kahoku Shimpo, Nikkei Sangyo, and Nikkan Kogyo) and broadcasted by NHK, Sendai TV, and Miyagi TV (January 26th, Japan time).
Jan. 2007
  In Kawazoe laboratory, Professor emeritus Hiroshi Yasuhara predicted that the most important contribution in the formation of materials is the electron-nucleus attractive interaction. According to this prediction, Dr. Kenta Hongo worked out a very accurate numerical calculation for hydrogen molecule by diffusion quantum Monte Carlo method, and proved it. In most of the standard textbooks, famous Heitler-London model or minimum basis molecular orbitals method are introduced, where the stability of materials is explained by a complete misunderstanding of reducing kinetic energy T and increasing potential energy V. Many similar mistakes have also been conducted by the ab initio calculations or theoretical model calculations, where only the total energy E is considered as the parameter for the stability. For isolated many-body Coulombic system, virial theorem (2T+V=0) holds and T and V are not independent. Accordingly E=T+V=-T=V/2, and when materials are formed from atoms, electrons come closer to the nucleus positions to earn potential energy, and T increases. Although this conclusion has already been stated from 60s, this is the first time to compute very accurately each part of energy with complete inclusion of electron exchange-correlations. This result was reported in Nikkei Nanobuisness journal in November and attracted a lot of interests, and will be published in International Journal of Quantum Chemistry.