Successful Growth of a Nano-Crystal Thin Film Systematically Oriented with a 3D-Porous Material (Press Release)
- Release Date
- 19 Jul, 2012
- BL13XU (Surface and Interface Structures)
Japan Synchrotron Radiation Research Institute
Kyoto University
National Institute for Materials Science
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A joint research group of the Japan Synchrotron Radiation Research Institute (JASRI), the National Institute for Materials Science, and Kyoto University has succeeded in creating a crystal thin film with a thickness in the order of nanometers in which 3-dimensionally rigid porous coordination polymers (hereafter PCPs)*1 are systematically oriented in a specific direction. The research group confirmed that this thin film is capable of a reversible gas adsorption/desorption reaction. PCPs with high gas-adsorption characteristics and high regularity (highly crystalline) are expected to have diverse functions, such as highly efficient separation and concentration of gas molecules, and reactions in the porous interior; therefore, by integrating various PCPs with different functions, we would be able to produce a variety of energy-related element devices, such as highly efficient fuel cells. For the architecture of such element devices, it is necessary to integrate different types of PCPs closely together, so multiple PCP film crystals must be produced in such a way that the crystals are systematically oriented in the same direction (oriented growth). However, at present, oriented growth has not been successful except for 2-dimensionally (plane) rigid PCPs. Thus, in order to obtain diverse functions, durable devices, and adhesion between different types of PCPs for integration, researchers had been eagerly seeking a technology that would enable oriented growth of crystals of 3-dimensionally rigid PCPs. This research group has successfully produced a nano-thin film of 3-dimensional PCPs with oriented growth by choosing a substrate appropriate for oriented growth, a surface fabrication method, and skeleton-forming materials that can control the growth orientation while being rigid in 3-dimensional directions. Furthermore, the group has confirmed that this nano-thin film shows a reversible gas adsorption/desorption reaction and that this adsorption/desorption reaction does not accompany any change in the skeletal structure, verifying its rigidity. This confirmation of both the oriented growth and the structural change in adsorption/desorption of the nano-thin film was made possible only through high-precision diffraction experiments using a high-luminance X-ray at SPring-8*2, a large synchrotron radiation facility. This research result is basically foundational technology to produce new function devices in which PCPs with various functions are integrated; it thus significantly speeds up research and development of function devices made with nano-thin film, and one can expect diverse applications of this technology, such as enhancing the performance of fuel cells. This project was carried out as part of the research topic “Creation of the Metal-Organic Hybrid Protonics and Functional Nano-Layer Integrated System” (Hiroshi Kitagawa, research director) under the research domain “Development of the Foundation for Nano-Interface Technology,” a team research project of the Core Research for Evolutional Science and Technology (CREST) under the auspices of the Japan Science and Technology Agency (JST), and also as an application research topic for SPring-8, a large synchrotron radiation facility. The original article on the results of this research was published on the June 13 issue of an American science journal, The Journal of the American Chemical Society. Publication: |
<<Figures>>
PCPs form their regular, systematic skeleton (bottom of the figure) as the metal ions and ligands assemble themselves. Pores thus created within PCPs are expected to have functions such as the separation, storage, and condensation of gas, as well as a catalytic reaction and polymer synthesis. They are also expected to have different conditions and functions when there is an external stimulus, such as light.
Thin-film component elements are alternatingly placed on top of a self-assembled monolayer (SAM) formed by 4-mercaptopyridine on a monocrystal silicon substrate with a thin metal film (silicon, chrome, or gold substrate). 2-dimensional layers formed with iron ions and tetracyanoplatinum complexes (square lattice surfaces in red, gray, and blue) and column-like pyrazines of ligands (six-membered rings in the figure) are built up in an alternating fashion. After thirty (30) cycles of this process, a 3D oriented polymer nano-thin film is formed on the substrate. Oriented crystal growth with a skeleton rigid in 3-dimensional directions was successfully achieved because of the coordinate bond within each layer and in the column structure.
(a) in-plane placement, including information in the direction parallel to the substrate surface
(b) XRD profile with out-of-plane placement, including information in the direction perpendicular to the substrate surface (the blue dots indicate the test results; the red line is the fitting curve of the test results; the green line is the simulation result; the “plus” signs show the peak positions of diffraction lines in the test results; the inserted figure on the left shows the measuring arrangement; and the inserted figure on the right shows the periodic structure of the polymer obtained by each profile). In each profile, we observed an independent diffraction line, underscoring the fact that the thin film obtained has crystalline both in the in-plane and the out-of-plane directions. Further, the simulation (green line) obtained from the bulk structure matches the profile (blue dots) obtained in this experiment almost perfectly. The peaks observed in-plane (a) represent only the periodicity within each 2-dimensional layer, while the peaks observed out-of-plane (b) represent only the periodicity between 2-dimensional layers through the column-forming pyrazines, clearly suggesting the perfect crystal orientation of the structure.
<<Glossary>>
*1 Porous Coordination Polymer (PCP)
A metal complex attracting much attention as a third porous material after activated carbon and zeolite; it is also referred to as a metal-organic framework (MOF). Adsorbents, such as activated carbon and zeolite, are substances that take in molecules for adsorption; they contain many small holes, and are therefore termed “porous materials.” Advantages of PCPs include their porosity, which is higher than that of zeolite, and their regularity (crystalline), which is higher than that of activated carbon. PCPs are also rich in designability and diversity as an agent group. Currently PCPs are being studied extensively as their pore size and shape can easily be controlled by replacing the structure elements and as the hydrophilic/hydrophobic nature of their pore walls can also be controlled.
*2 SPring-8
A RIKEN facility located in Harima Science Garden City (Hyogo prefecture) is capable of producing the world's highest intensity synchronous radiation. The management and promotion of utilization of this facility are undertaken by JASRI. The name “SPring-8” comes from “Super Photon ring-8GeV.” An electron flying at nearly the speed of light, if deflected from its original trajectory through the effect exerted by a magnet, emits an electromagnetic wave in a direction tangential to its trajectory, which is called radiation light (or synchrotron radiation). At present, there are three “3rd Generation” large scale synchronous radiation facilities in the world: SPring-8 (Japan), APS (USA) and ESRF (France). The acceleration energy available at SPring-8 (8 billion electron volts) enables the provision of an extremely wide spectrum of radiation light: from far infrared to visible, vacuum ultraviolet, and soft X-ray up to hard X-ray. SPring-8 provides a theater for collaborative works involving researchers inside and outside Japan, and the research conducted at this facility cover such diverse areas as material science, geoscience, life science, environmental science, and various applications in industrial sectors.
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For more information, please contact:
Ph.D Akihiko Fujiwara (JASRI)
Assistant Prof. Kazuya Otsubo (Kyoto University)
Prof. Hiroshi Kitagawa (Kyoto University) |
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