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2008 | Buch

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Frontiers in Materials Research

herausgegeben von: Professor Yasunori Fujikawa, Professor Kazuo Nakajima, Professor Toshio Sakurai

Verlag: Springer Berlin Heidelberg

Buchreihe : Advances in Materials Research

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

New advanced materials are being rapidly developed, thanks to the progress of science. These are making our daily life more convenient. The Institute for Materials Research (IMR) at Tohoku University has greatly contributed for to the creation and development of various advanced materials and the progress in the ?eld of material science for almost a century. For example, our early research achievements on the physical metallurgy of iron carbon alloys led to the innovation of technology for making high-quality steels, which has greatly contributed to the advancement of the steel and related industry in Japan and rest of the world. IMR has focused on basic research that can be translated into applications in the future, for the bene?t of mankind. With this tradition, we have established the ?rst high-magnetic ?eld as well as low-temperature technologies in Japan, which were essential to the - vancement of magnetism and superconductivity. Recently, IMR has expanded its research in the ?eld of advanced materials including metallic glasses, - ramics, nano-structural metals, semiconductors, solar cell crystals, new op- andspin-electronicsmaterials,organicmaterials,hydrogenstoragealloys,and shaped crystals. Inthefaceofthecrisisofthedestructionoftheglobalenvironment,the- pletion of world-wide natural resources, and the exhaustion of energy sources in the twenty-?rst century, we all have an acute/serious desire for a b- ter/safer world in the future. IMR has been and will continue the pursuit of research aimed at solving global problems and furthering eco-friendly dev- opment.

Inhaltsverzeichnis

Frontmatter

Novel Materials for Electronics

1. Science, for the Benefit of Mankind

The crucial role of a comprehensive education for science at all levels for the general progress of mankind, for economic development, for political maturity, and for worldwide stability is widely recognized — no education, no progress, no development, no maturity, no stability. Yet, reality is lagging far behind and we are still far away from a world wide education for all, even what an education on the most rudimentary level is concerned. Looking at the development aide efforts, it appears to me more like “Development, for the benefit of the developed ones” or “Education, for the benefit of the educated ones.” And here we get readily lost in the thicket of conflicting economic and political interests. Finding acceptable and practical ways out lies, I believe, beyond this workshop.

Education comes to bear on mankind in many ways. On the top level, education provides the foundation of science; thus the benefit of education is mediated to mankind by science: Science, for the benefit of mankind. In the following, Science refers mainly to University research and education and to research at dedicated and mostly publicly funded research institutions.

Alfred Nobel was one of the first convinced believers in “Science, for the Benefit of Mankind” by bequeathing his tremendous fortune to honor scientific achievements for their benefit on mankind. In his legacy, we read “…Shall be annually distributed in the form of prizes to those who shall have conferred the greatest benefit on mankind.” And he continues: “…one part to the person who shall have made the most important discovery or invention within the field of physics….”

H. H. Rohrer

2. Trends of Condensed Matter Science: A Personal View

Summary

A personal view on the development of the research activities in condensed matter sciences is presented, with special emphasis on the carrier doping into insulators, which have been classified into four categories: band insulators, Mott insulators, charge ordering, and Anderson localization. Depending on these parent insulators, doped carriers behave essentially differently as typically seen in semiconductors (doped band insulators) in contrast to high T _c cuprates (doped Mott insulators) as bulk materials. Thanks to the establishment of experimental capabilities to probe local properties initiated by the success of scanning tunneling microscope (STM), more attentions are naturally being paid to local structures and associated electronic properties, spectroscopy in particular, which eventually govern material properties in macroscopic scales. Typical research targets from this viewpoint may include (1) strongly correlated electron systems, (2) surfaces, interfaces, and contacts, and (3) molecular assemblies. With more detailed explanation of the recent remarkable progress of the understanding of molecular solids belonging to above three, a hope is expressed that time is ripe to develop studies on bio-related materials, such as proteins and DNA, based on the well established technique in condensed matter science just as natural extensions of those on molecular solids. A tentative list of concrete research targets along this line of bio-material science has been proposed.

H. Fukuyama

3. Measurements and Mechanisms of Single-Molecule Conductance Switching

Summary

We have engineered and analyzed oligo(phenylene-ethynylene) (OPE) derivatives to understand and to control the bistable conductance switching exhibited by these molecules when inserted into saturated alkanethiolate and amidecontaining alkanethiolate self-assembled monolayers (SAMs) on Au{111}. By engineering the structures of the OPE derivatives, we have shown conductance switching to depend on hybridization changes at the molecule–substrate interface. In addition, we have demonstrated bias-dependent switching controlled by interactions between the dipole of the OPEs and the electric field applied between the scanning tunneling microscope tip and the substrate. These interactions are stabilized via intermolecular hydrogen bonding between the OPEs and host amide-containing SAMs.

A. M. Moore, B. A. Mantooth, A. A. Dameron, Z. J. Donhauser, P. A. Lewis, R. K. Smith, D. J. Fuchs, P. S. Weiss

4. Exploration of Oxide Semiconductor Electronics Through Parallel Synthesis of Epitaxial Thin Films

Summary

A review is given for advanced thin film technology based on pulsed laser deposition of oxide thin films. Atomically regulated epitaxy has been extended to various kinds of oxides to construct artificially made heterostructures. Computer controlled masking and target switching in pulsed laser deposition have made it possible to integrate number of thin films with different layered structures and/or various compositions. This technique has been applied to search for new materials and functionalities in such oxide semiconductors as ZnO and TiO₂. The highlights of magnetic, photonic, and electronic devices are introduced with examples of TiO₂ ferromagnetic junctions, ZnO light emitting diodes, and (Mg, Zn) O/ZnO quantum Hall devices, respectively.

M. Kawasaki

5. Epitaxial Growth and Transport Properties of High-Mobility ZnO-Based Heterostructures

Summary

Optimization of growth conditions is most important for extracting desired material properties, but it always requires time-consuming experiments. The temperature gradient method was applied for high-throughput optimization of the growth temperature by pulsed laser deposition to ZnO-based heterostructures. Surface morphology, photoluminescence, and electrical transport properties depend systematically on the growth temperature. Consequently, enhancement of two-dimensional growth, as detected from atomic force microscope images, can elucidate good physical properties, e.g., the observation of higher-order exciton emissions and highest electron mobility. By further optimizing the structure of heterojunction, we found growth conditions enabling the quantum Hall effect at the ZnO / Mg_xZn_1−xO heterointerface.

A. Tsukazaki, A. Ohtomo, M. Kawasaki

6. A Scaling Behavior of Anomalous Hall Effect in Cobalt Doped TiO2

Summary

Anomalous Hall effect (AHE) is a generally observed phenomenon in ferromagnetic metals representing spin polarized nature of itinerant carriers. However, the microscopic mechanism has not been clarified for long debates. Recent advances in the theory are to unveil the mechanism. Here, we present an AHE in a room temperature ferromagnetic semiconductor cobalt doped TiO₂. This compound shows a scaling behavior of the AHE: the anomalous Hall conductivity σ_AH approximately follows the relation σ_AH ∞ σ_xx ^1.6 (σ_xx, conductivity) over five decades of σ_xx, irrespective of the electronic state, i.e., metallic or insulating conduction.

T. Fukumura, H. Toyosaki, K. Ueno, M. Nakano, T. Yamasaki, M. Kawasaki

7. Synthesis, Phase Diagram, and Evolution of Electronic Properties in LixZrNCl Superconductors

Summary

We succeed in synthesizing a series of single phase Li_xZrNCl samples with controlled doping levels (0 ≤ x ≤ 0.31) by adopting an appropriate annealing procedure for lightly doped samples. An insulator-to-superconductor transition was found to occur at approximately x = 0.05, and the superconducting transition temperature (T _c) anomalously increases rapidly below x = 0.12 as the insulating phase is approached from the superconducting side. Doping and temperature-dependent Raman scattering measurements indicated that electron–phonon interaction strength rather decreases upon reducing carrier concentration, suggesting that charge fluctuation plays an important role in the enhancement of T _c in the reduced carrier density regime.

Y. Taguchi, A. Kitora, T. Takano, T. Kawabata, M. Hisakabe, Y. Iwasa

8. Ambipolar Tetraphenylpyrene (TPPy) Single-Crystal Field-Effect Transistor with Symmetric and Asymmetric Electrodes

Summary

An ambipolar field-effect transistor (FET) based on a 1,3,6, 8-tetraphenylpyrene (TPPy) single-crystal, a high photoluminescent material, has been successfully fabricated using symmetric and asymmetric electrodes. Several kinds of metal electrodes have been employed to investigate the charge injection characteristics in the single-crystal FET. Hole and electron mobilities of 0.34 and 7.7 × 10⁻²cm² V⁻¹ s⁻¹ were achieved by using Au and Ca electrodes, respectively. The ambipolar characteristic of this device gives a prospect for further development in light-emitting FET operation.

S. Z. Bisri, T. Takahashi, T. Takenobu, M. Yahiro, C. Adachi, Y. Iwasa

9. Bulk Zinc Oxide and Gallium Nitride Crystals by Solvothermal Techniques

Summary

We report on recent achievements from the growth of hydrothermal zinc oxide (ZnO) and ammonothermal gallium nitride (GaN). A thin-film deposition technique under conditions near the thermodynamic equilibrium, liquid phase epitaxy (LPE) is applied for fast screening of dopants and their effects on physical properties of ZnO. In particular, super fast luminescent decay will be reported from some donor-acceptor co-doped ZnO films prepared by LPE.

D. Ehrentraut, T. Fukuda

Materials for Ecological and Biological Systems

10. High-Quality Si Multicrystals with Same Grain Orientation and Large Grain Size by the Newly Developed Dendritic Casting Method for High-Efficiency Solar Cell Applications

Summary

Si multicrystals have many grains with different orientations and sizes, resulting in many grain boundaries with different characteristics. To obtain the high conversion efficiency of the solar cells prepared by Si multicrystals that is very close to that of Si single crystals, Si multicrystals that have grains with a same orientation and proper sizes and have electrically inactive grain boundaries are required. This concept was tried and the dendritic casting method was newly developed to obtain extremely high-quality Si multicrystal ingots and to largely increase the yield of high-quality Si multicrystal ingots. To develop such a new growth technology by understanding the crystal growth mechanism to control the grain orientation and the grain size, the in-situ observation system was newly developed to directly observe the growing interface of Si crystals at temperatures higher than l,400°C. Using the in-situ observation system, it was found that the new growth mode of Si dendrite crystals appeared along the bottom of the crucible at the initial stage of the growth. Such dendrite crystals were very effective to control the grain orientation and the grain size of Si multicrystals. Using the developed dendritic casting method, extremely high-quality Si multicrystal ingots with the same grain orientation and very large grain size were obtained. The conversion efficiency of the solar cells prepared by such Si multicrystals was much higher than that of the solar cells with different grain orientations, especially for the upper parts of the Si ingots.

K. Nakajima, K. Fujiwara, N. Usami

11. Growth of High-Quality Polycrystalline Si Ingot with Same Grain Orientation by Using Dendritic Casting Method

Summary

We succeeded in the development of a new technique to grow a high-quality polycrystalline Si ingot for solar cells named as “Dendritic casting method,” which utilizes the dendrite growth along the bottom of the crucible wall at the initial stage of directional growth. This method permits to obtain a textured polycrystalline Si ingot with large-size grains. Furthermore, its crystal quality was revealed to be highly maintained from the bottom to the top in the ingot, which is a great advantage from a view of the material yield. Solar cells based on this polycrystalline Si show high energy conversion efficiencies close to that of Si single crystal solar cells.

K. Fujiwara, W. Pan, N. Usami, M. Tokairin, Y. Nose, A. Nomura, T. Shishido, K. Nakajima

12. Floating Cast Method as a New Growth Method of Silicon Bulk Multicrystals for Solar Cells

Summary

We propose a new growth method named as floating cast method to realize high-quality Si bulk multicrystals for solar cells. The fundamental concept of floating cast method is to perform crystal growth from the top center of Si melt in a crucible without contacting the inner wall until the melt is entirely solidified. By using a small scale furnace, crystals were grown under the concept of floating cast method and by the conventional casting method. As a result, resistivity in the crystal grown by floating cast method was found to be higher, which implies less contamination from the coating material at the crucible wall. In addition, fewer defects such as grain boundaries and dislocations were observed. The conversion efficiency of solar cells based on the crystals grown by floating cast method was revealed to be higher than that by the conventional casting method. Therefore, floating cast method, we propose in this paper, is much promising, which could potentially solve problems in the conventional casting methods and realize high-quality Si bulk multicrystals with fewer impurities and defects.

I. Takahashi, Y. Nose, N. Usami, K. Fujiwara, K. Nakajima

13. Dehydriding Reaction of Hydrides Enhanced by Microwave Irradiation

Summary

Effects of microwave irradiation on the dehydriding reaction of metal hydrides MH_n (LiH, MgH₂, CaH₂, TiH₂, VH_0.81, ZrH₂ and LaH_2.48) and complex hydrides MBH₄ (LiBH₄, NaBH₄ and KBH₄) were systematically investigated. Among the metal hydrides, TiH₂, VH_0.81, ZrH₂, and LaH_2.48 exhibited a rapid heating by microwave irradiation, where a small amount of hydrogen (less than 0.5 mass%) were released. On the other hand, LiBH₄ was heated above 380 K by microwave irradiation, where 13.7 mass% hydrogen was released. The rapid heating of metal hydrides such as TiH₂, VH_0.81, ZrH₂, and LaH_2.48 are mainly due to the conductive loss. Meanwhile the microwave heating in LiBH₄ is attributed to the conductive loss, which is caused by a structural transition. Furthermore, microwave was irradiated to the composites of LiBH₄ and TiH₂. The composites exhibited faster temperature increases than pure LiBH₄, which resulted in faster dehydriding reaction of LiBH₄. Microwave heating might be applied to hydrogen storage system, though further development of hydrides themselves and engineering techniques are required.

M. Matsuo, Y. Nakamori, K. Yamada, T. Tsutaoka, S. Orimo

14. Mechanically Multifunctional Properties and Microstructure of New Beta-Type Titanium Alloy, Ti-29Nb-13Ta-4.6Zr, for Biomedical Applications

Summary

A new biomedical titanium alloy, Ti-29Nb-13Ta-4.6Zr, composed of nontoxic elements like Nb, Ta, and Zr, has recently been developed in order to achieve a lower Young’s modulus similar to that of human hard tissues in addition to excellent mechanical properties for use as structural biomaterials. The characteristics of this material depend on the microstructures obtained by heat treatments or thermomechanical treatments. Therefore, the relationship between microstructures and basic mechanical properties, the Young’s modulus, tensile and fatigue properties, etc., has been investigated with respect to Ti-29Nb-13Ta-4.6Zr. Further, the practical performance of this alloy as a metallic biomaterial has been evaluated via animal experiments. Moreover, the mechanical functionalities of this alloy, such as superelasticity, were reported recently. In the present paper, the accumulated reports on Ti-29Nb-13Ta-4.6Zr were summarized and the mechanical properties of this alloy were mainly reviewed in order to evaluate its potential for biomedical applications.

M. Nakai, M. Niinomi, T. Akahori

Precise Control of Microscopic and Complex Systems

15. Atom Probe Tomography at The University of Sydney

Summary

The Australian Microscopy & Microanalysis Research Facility (AMMRF) operates a national atom probe laboratory at The University of Sydney. This paper provides a brief review and update of the technique of atom probe tomography (APT), together with a summary of recent research applications at Sydney in the science and technology of materials. We describe recent instrumentation advances such as the use of laser pulsing to effect time-controlled field evaporation, the introduction of wide field of view detectors, where the solid angle for observation is increased by up to a factor of ~20 as well as innovations in specimen preparation. We conclude that these developments have opened APT to a range of new materials that were previously either difficult or impossible to study using this technique because of their poor conductivity or brittleness.

B. Gault, M. P. Moody, D. W. Saxey, J. M. Cairney, Z. Liu, R. Zheng, R. K. W. Marceau, P. V. Liddicoat, L. T. Stephenson, S. P. Ringer

16. A Study on Age Hardening in Cu-Ag Alloys by Transmission Electron Microscopy

Summary

We have prepared Cu-1, 2, 4 at % Ag alloys by arc-melting and investigated their age-hardening and precipitation behaviors by using hardness tests, conductivity measurements, and TEM. The evolution of hardness during annealing exhibited strong composition dependence: the 4 at % Ag alloy aged for 20 min at 450°C already showed the maximum hardness, while the 2 at % Ag alloy began to harden after 9 h ageing. The maximum hardness was followed by gradual decrease, while electrical conductivity steadily increased to nearly 90% IACS. The observed precipitates in the 4 at % Ag alloy aged for 20 min consist of rod-shaped fee Ag precipitates, which grow in the [110]_Cu direction, and whose cross-sections are elliptic with an ellipticity greater than two. Widely interspaced precipitates then appear abruptly in the 4 at % Ag alloy aged for 27 h. These observations have been discussed from the view points of the morphology and crystallography.

E. Shizuya, T. J. Konno

17. Rubber-Like Entropy Elasticity of a Glassy Alloy [1]

Summary

The thermoelastic effect is monopolistically characteristic of rubbers in solids. Here we report observations of thermal-induced entropy elasticity for a glassy alloy, Pd₄₀Cu₃₀Ni₁₀P₂₀ in terms of acoustoelasticity and the Gough–Joule effect. Seven kinds of elastic parameters of the glassy alloy have been simultaneously measured as a function of temperature ranging from 298 to 673 K. The decreases in elastic moduli, Poisson’s ratio, and the increase in tension below the second-order like-phase transition temperature suggest rubber-like thermal dynamic micro-Brownian stretching, described as F (Pa) = 0.282 T + 562, which may be associated with the rotational and vibrational motions of polyhedron clusters. The glassy alloy also showed the Gough–Joule effect at room temperature. In short, the glassy alloy has some rubbery characteristics that we have never before observed for ordinary crystalline alloys and inorganic materials.

M. Fukuhara, A. Inoue, N. Nishiyama

18. Formation and Mechanical Properties of Bulk Glassy and Quasicrystalline Alloys in Zr-Al-Cu-Ti System

Summary

The glass-forming ability (GFA) of Zr₆₅Al_7.5Cu_27.5 alloy can be improved effectively by a certain amount of Ti addition. Bulk glassy samples of 3 mm in diameter were obtained in the compositions containing 3–7 at% Ti by copper mold casting, while further Ti additions will deteriorate GFA and lead to the formation of quasicrystals at (Zr₆₅Al_7.5Cu_27.5)₉₀Ti₁₀. Meanwhile, the addition of Ti in the Zr₆₅Al_7.5Cu_27.5 alloy was found to alter the crystallization behavior of the metallic glasses; thus bulk quasicrystalline alloy can also be achieved by glass devitrification of Ti-containing BMGs. Room-temperature compression testing showed that bulk quasicrystalline alloy, fabricated either by mold casting or by glass devitrification method, exhibited higher fracture strength and Young’s modulus than that of the relative monolithic BMGs.

J. B. Qiang, W. Zhang, G. Q. Xie, A. Inoue

19. Fabrication and Characterization of Metallic Glassy Matrix Composite Reinforced with ZrO2 Particulate by Spark Plasma Sintering Process

Summary

We have fabricated Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glassy matrix composite by a spark plasma sintering process using a mixed powder of gas-atomized Zr₅₅Cu₃₀Al₁₀Ni₅ glassy alloy powders blended with 10 vol. % ZrO₂ powders. The structure, thermal stability, and mechanical properties of the sintered bulk glassy matrix composite were investigated. The ZrO₂ particles were homogeneously dispersed in the Zr₅₅Cu₃₀Al₁₀Ni₅ glassy matrix. No crystallization of the glassy matrix occurred during the spark plasma sintering process. The crystallization behavior of the sintered glassy matrix composite was similar to that of the glassy alloy powder. The plastic ductility of the sintered Zr₅₅Cu₃₀Al₁₀Ni₅ glassy matrix composite was enhanced by adding the ZrO₂ particulates into the metallic glassy alloy. The improvement was originated from the structural inhomogeneity caused by the micro-particles inclusion.

G. Q. Xie, D. V. Louzguine-Luzgin, W. Zhang, H. Kimura, A. Inoue

20. Nucleation and Growth of Thin Pentacene Films Studied by LEEM and STM

Summary

The application of the low-energy electron microscopy (LEEM) to the in-situ, real-time investigations of the nucleation and growth of organic pentacene (Pn) thin films is discussed. The relation between the substrate surface reactivity and the Pn film growth mechanisms is evidenced. We also discuss the anisotropy in the Pn film growth under kinetically limited growth conditions, which results in preferential growth of Pn in the direction of the b-axis, of the in-plane unit cell. We show how this kinetic preference can dramatically affect the crystallinity of the organic film, on the example of self-polycrystallization in epitaxial Pn films on H-Si(111) surface.

J. T. Sadowski, A. Al-Mahboob, Y. Fujikawa, T. Sakurai

21. Mechanism of Chiral Growth of 6, 13-Pentacenequinone Films on Si (111)

Summary

Thin film growth of 6, 13-pentacenequinone, (C₂₄H₁₂O₂, PnQ), on Si (111)-7 × 7 at room temperature (RT) was studied by low-energy electron microscopy (LEEM) and ab initio density functional theory (DFT) calculations. Our experiments yielded direct microscopic observation of enantiomorphic evolution mechanism in the initial stage of the chiral-like growth of PnQ islands under kinetic growth conditions. We observed that the faster growth direction aligns with the direction of easier molecule incorporation, or lowest kink formation energy, rather than along the lowest energy step. Real time observation of the growth and subsequent relaxation of island shape revealed that kinetically stiff direction differs from the thermodynamic one. This feature together with anisotropic mass incorporation determines the enantiomorphic evolution and rotational arrangement of crystallites during the growth of elongated organic molecules, like PnQ.

A. Al-Mahboob, J. T. Sadowski, T. Nishihara, Y. Fujikawa, T. Sakurai

22. GaN Integration on Si via Symmetry-Converted Silicon-on-Insulator

Summary

Integration of metals and semiconductors having three- or sixfold symmetry on device-oriented (i.e., (001)) silicon wafers, which have fourfold symmetry, has been a longstanding challenge. We demonstrate that, by using symmetry-converted (111) silicon-on-insulator, we can integrate wurtzite-structure gallium nitride, which has threefold symmetry, with Si (001). The stability of the symmetry-converted Si (111) layer makes this technique appealing to the commercial integration of wide-ranging important materials onto Si (001) base wafers.

Y. Fujikawa, Y. Yamada-Takamura, Z. T. Wang, G. Yoshikawa, T. Sakurai

23. Functional Probes for Scanning Probe Microscopy

Summary

Functional probes for scanning probe microscopy (SPM) were fabricated with focused ion beam (FIB) method. Metal-tip cantilevers were fabricated for Kelvin probe force microscopy (KFM) and glass-coated tungsten tips were fabricated for scanning tunneling microscopy under irradiation of synchrotron-radiation light (SR-STM). Here we report the fabrication process and the characterization of those functional probes.

K. Akiyama, T. Eguchi, M. Hamada, T. An, Y. Fujikawa, Y. Hasegawa, T. Sakurai

Titel: Frontiers in Materials Research
herausgegeben von: Professor Yasunori Fujikawa
Professor Kazuo Nakajima
Professor Toshio Sakurai
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-540-77968-1
Print ISBN: 978-3-540-77967-4
DOI: https://doi.org/10.1007/978-3-540-77968-1

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