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Nanotechnology / Materials: 26
Advanced Nano-optical Lithography Using Plasmons
Optical lithography technology with single-nanometer processing resolution
Using localization of the photoelectric field by plasmon resonance, the photoelectric field can be freely localized in a small area. With this technology, we have invented optical lithographic technology with a resolution of several nm by using the scattered light of the higher-order resonance mode of the plasmon.
While the resolution of conventional optical lithography is determined by the wavelength, this lithographic technology is determined by the processing resolution of the metal nanostructure of the photomask. By irradiating the metal nanostructure of the photomask with infrared light, this technology can transfer patterns with the resolution of a single nanometer. This technology is unique since the shape of the mask pattern can be transferred as such by simply irradiating it with infrared light, high aspect ratio processing is expected because light propagation is used instead of near-field light, and it is possible to not only produce line and space patterns but also triangle, nano-gap, chain, and other shapes. It is expected to apply this technology to photonic crystals, plasmonic solar cells, and the technology for moth-eye structure formation on the surface of optical elements, which requires the transfer of nano-patterns over a relatively large area.
Artificial Photosynthesis System Using Localized Plasmons
Ammonia photosynthesis system involving hydrogen produced from water by visible and near-infrared light using an optical nano-antenna
To realize highly efficient artificial photosynthesis, we have used an optical nano-antenna made of metal nanostructures to convert solar energy to a wide range of wavelengths from visible to near-infrared, succeeding in hydrogen generation based on the photolysis of water and the photosynthesis of ammonia, which has recently attracted attention as an energy carrier.
To realize highly efficient artificial photosynthesis, it is essential to convert the energy into chemical substances by constructing a system that utilizes solar energy of visible and near-infrared wavelengths, which are not used in conventional artificial photosynthesis. We have succeeded in designing and fabricating an optical nano-antenna that can effectively collect light of various wavelengths by changing the shape and arrangement of the metal nanostructures. We have also successfully photodisintegrated water to produce hydrogen and oxygen stoichiometrically using sunlight in a wide range of wavelengths from visible to near-infrared. This system has also enabled us to photosynthesize ammonia through photoreduction of nitrogen in the air. Ammonia is attracting attention as a next-generation energy carrier, but its synthesis requires high-temperature and -pressure conditions, which may cause a huge environmental burden. This system is expected to be used as a method for ammonia synthesis at normal temperature and pressure using sunlight.
Clarifying the Physical Constants of Electron Spin Control
Accelerating the research and development of next-generation electronic devices
Among various semiconductor properties, we have quantitatively clarified the previously unknown “spin-orbit interactions” of n-type quantum well structures based on InGaAs semiconductors, including gate voltage dependence. This achievement will be a seed for the development of next-generation spin devices.
Existing semiconductor devices operate through the electric charge of electrons. In addition to the electric charge, an electron also has the other property of spin, which is a magnetic property. The electron spin in a solid can be aligned in a certain direction (Fig. 1a) or rotated about a specific axis (Fig. 1bc), depending on the situation. The key to realizing next-generation electronic devices is to control such electron spin in semiconductor devices. In this study, we used indium-, gallium-, and arsenic-based field-effect transistors (Fig. 2) and performed electrical measurements in a cryogenic environment (absolute temperature of 20 mK) using a dilution refrigerator (Fig. 3). In this way, we were able to precisely determine for the first time the spin-orbit interaction coefficient, which is necessary to control electron spin (Fig. 4).
Creation of Highly Active Catalysts Using Polystyrene-bridged Bisphosphine Ligands
Design of metal complex catalysts using polymeric carriers as the reaction site and development of an efficient synthetic processes
We have developed polystyrene-crosslinked bisphosphine ligands that can be used to create polymer-supported metal catalysts. Thanks to the effect of polymer topology, it is possible to suppress disproportionation of metal complexes and deactivation of catalysts caused by metal aggregation. It is particularly useful as a ligand for first transition series metal catalysts.
Heterogeneous (insoluble) metal catalysts, which are easy to separate from the reaction mixture and have excellent reusability, can be used for organic synthesis in an environmentally-friendly manner. However, compared with the corresponding homogeneous (soluble) catalysts, they have a problem of reduced catalytic activity. We have developed a polystyrene-crosslinked bisphosphine ligand, PS-DPPBz, based on the topological control of polymer chains. Since this ligand is effective in generating highly active monochelate mononuclear transition metal complexes, it has significantly improved the efficiency of Ni-catalyzed reactions such as amination coupling of aryl chlorides and ester-azole coupling. PS-DPPBz can also be used for substrates to which it is difficult to apply existing catalysts. PS-DPPBz can be separated by filtration and reused, so it is expected to use this catalyst for industrial purposes.
Development of Innovative Anodized Aluminum and Their Functions
When the surface changes, everything changes.
We will introduce our research on the development of superior properties and new functions of aluminum by innovation of anodizing, which is an extremely well-known corrosion-resistant passive coating for aluminum.
Anodic oxide film is an artificial passive film formed on the surface of aluminum, and was developed in Japan about 100 years ago. There are many anodized aluminum products around us, but our research group is reviewing the chemical substances and formation methods (anodic oxidation) used to form anodized aluminum surfaces from the ground up, and we try to develop a new anodizing method that exhibits superior properties and innovative functions. Specifically, we are developing anodized aluminum with highly ordered nanostructures, hard anodized aluminum with a Vickers hardness of Hv = 600 or higher, anodized aluminum with high corrosion resistance in acid, base, and chloride environments, and anodized aluminum that shines beautifully by producing luminescence and structural colors.
Development of Microstructure Prediction Simulation Technology for Metallic Materials
From solidification to solid phase transformation
In the manufacturing process of structural and functional materials, various material structures are formed during solidification, heat treatment, and plastic processing, and the characteristics of these structures determine the properties of the materials. We are developing a simulation method to predict the series of material microstructure changes from solidification to solid phase transformation.
We are developing and applying methods for predicting temporal changes in the microstructure of metallic materials during the series of phase transformations that occur in the manufacturing process, such as solidification, grain growth, and diffusional solid transformation. We are specifically engaged in the development of a phase-field model, a method to simulate microstructure formation, and have succeeded in developing a model that calculates the diffusional phase transformation with the highest accuracy in the world. We are also working on microstructure control in various alloy systems by combining experimental approaches, atomistic approaches using molecular dynamics, and information science approaches such as data assimilation and machine learning. We are developing new theories of microstructure formation by using ultra-large scale calculations and obtaining results that lead to optimization of the actual processes.
Electrochemically Responsive Organic Dyes
From electrochromism to multiple responses (fluorescence, circularity)
Based on cationic organic dyes, which allow easy control of color tone, we offer a group of materials that can respond in multiple ways, including fluorescence and optical rotation (circular dichroism). This technology is designed to suppress the decomposition process of reduced species, and the bi-stability of oxidized and reduced species is such that exchange does not occur, even when they are mixed.
Electrochromism is a general term for compounds that change their color tone in response to changes in external electrical potential. As materials that can undergo reversible color changes, they are attracting attention as light control materials for smart windows and display functions for electronic paper. Materials of which not only the color tone, but also fluorescence, optical rotation (circular dichroism), etc. can be changed, enable tailor-made responses according to the application.
With this technology, we provide a group of substances with multiple responses based on cationic organic dyes of which the color tone can easily be controlled. The reduced species of cationic dyes are generally reactive, and the repeatability of the response is low, but with this technology, the decomposition process of the reduced species is suppressed by incorporating two cationic moieties. The bi-stability of the oxidized and reduced species, in which no exchanges occur, even when they are mixed, makes it possible to apply this technology to high-density recording materials.
Fabrication of High-speed Superhydrophilic Surfaces and Sliding-controlled Superhydrophobic and Superoleophobic Surfaces
Both water and oil can soak well into the surface, slide off it easily, and stick to it properly
We will show you how to create superhydrophilic surfaces that can rapidly be wetted and covered in water, and superhydrophobic and superoleophobic surfaces that repel water/oil very well although their sliding behavior can easily be controlled to allow water/oil to be adsorbed on the surface or easily slide off.
Anodizing is a technique used to form oxides with various nanostructures on the surface of metals. We have developed a method to form a large amount of nanofiber oxides with a diameter of sub-10 nm (10 nm or less) by anodizing using a novel electrolyte chemical species. The density of nanofiber formation is extremely high, in the order of 1010 nanofibers (10 billion nanofibers) per cm2. We have found that the metal surface formed with such high-density nanofibers exhibits fast superhydrophilicity of one second or less, as well as superhydrophobicity and superoleophobicity with controlled sliding behavior. It is also possible to mix surfaces with different wettability by using micropatterning techniques.
Hydrogenation with Homogeneous Palladium Nanoparticle Catalyst
Selective synthesis of cis-alkenes and amines
cis-Alkenes and amines, which are useful as raw materials for pharmaceuticals, agricultural chemicals and other chemical products, can be synthesized efficiently through hydrogenation of alkynes, organic nitro compounds and azides. The originally developed homogeneous palladium nanoparticles can be stored in solution for longer than a year and are easy to handle in air.
We have found that homogeneous palladium nanoparticles can be obtained by treating palladium acetate with potassium tert-butoxide or sodium borohydride in the presence of alkynes (Fig.1). The nanoparticles can be stored in solution for longer than a year and are easy to handle in air. They exhibit excellent performance as hydrogenation catalysts and can efficiently synthesize cis-alkenes (2) and amines (4 and 6) from alkynes (1), organic azide compounds (3) and aromatic nitro compounds (5), respectively. They have excellent cis-alkene selectivity and functional group tolerance (no loss of the ketone, aldehyde, or benzylic hydroxy group, etc.). The catalytic activity is extremely high; the reaction proceeds quickly using only 1/1000 to 1/5000 equivalent of palladium of the substrate (raw material). It also has excellent economic efficiency and convenience, and we are examining the possibility of commercializing it in cooperation with companies.
Infrared Metamaterials Produced by Microfabrication of High Temperature Resistant Materials
Development of materials and devices that manipulate mid- to far-infrared radiation
It is expected that it will be possible to make devices to control corresponding electromagnetic waves by creating heaters and diffraction gratings with patterns smaller than the mid- to far-infrared wavelengths. We are developing methods to fabricate thin films, stacks, and microstructures of metal carbides and oxides, and are studying their elemental characteristics.
Materials that are finely processed on a scale of less than the wavelength of electromagnetic waves can control the reflection and transmission of electromagnetic waves (such materials are known as metamaterials). Mid- to far-infrared radiation, with wavelengths ranging from 3 μm to 1000 μm, can be used for the detection of molecules as it is an electromagnetic wave that is related to heat radiation and can excite molecular vibrations. Since it is a heat-related material, being heat-resistant would render it usable for applications that cannot be realized elsewhere. We are studying process technology for heat-resistant materials with various properties such as metal carbides and oxides, and are measuring the fundamental properties of these materials in the infrared region for application to metamaterial design. By fabricating metamaterials for mid- to far-infrared radiation, we aim to create narrow linewidth mid-infrared light emitting devices for molecular detection and materials for controlling radiation heat.
Low Power Consumption Tunnel Transistors
Realizing next-generation energy-saving devices with new semiconductor interfaces
With this research we proposed and realized an unprecedented low-power FET/tunnel FET by applying a new semiconductor solid-phase interface, which is formed by very small nanowires a few thousandths of a hair’s width, to a switch element.
High performance of microprocessors and semiconductor integrated circuits, which are the brains of smartphones and PCs, have been achieved by reducing the size of field-effect transistors (FETs), which are the basic elements, and installing approximately 2 to 3 billion of them. While higher performance is being achieved, the rapid increase in power consumption of these FETs is becoming a serious problem. This is because there is a physical limit (60 mV/digit) on the switching performance (sub-threshold factor) of FETs. To realize drastic energy saving in the future, it is necessary to develop a new switch element that can break through the physical limit on FETs and their practical application. With this research, we have proposed and realized an unprecedented low-power-consumption tunnel FET.
Low-temperature Nitridation Method Using Sodium Amide
Nitride and oxynitride synthesis without using ammonia gas cylinder
This is a method used to convert oxides and other materials into nitrides and oxynitrides at low temperatures (300°C or less) by using a sodium amide melt to trigger a reaction with a highly concentrated and active nitrogen source. Nitrides and oxynitrides can be synthesized without having to prepare toxic ammonia gas cylinders.
This is a new method for nitridation of oxides at low temperatures (300℃ or less). Conventional nitridation methods require the installation of toxic ammonia gas cylinders and toxic ammonia gas recovery facilities, and also use a large amount of ammonia due to the low ammonia gas usage rate. With the present method, the use of sodium amide as a flux minimizes the use of toxic ammonia and makes it possible to obtain oxynitride and nitride nanocrystals at low temperatures. Since sodium amide is a solid nitrogen source, it eliminates the need to install ammonia liquid cylinders. We have also discovered a method to synthesize oxynitrides by mixing chloride and sodium amide through an instantaneous temperature-programmed reaction.
Mass Production of Nanofibrillated Bacterial Cellulose
Bottom-up production of nanofibrillated cellulose from low molecular weight biomass using bacteria
We have acquired a novel cellulose-synthesizing acetic acid bacterium and succeeded in the mass production of nanofibrillated bacterial cellulose (NFBC: Fibnano?) with excellent flowability, miscibility, and formability and that can be used in a wide range of fields, from molasses.
Cellulose synthesized by bacteria and called bacterial cellulose (BC) has unique properties such as high water retention, high strength, biodegradability, and biocompatibility. In recent years, nano-sized cellulose materials (nanofibrillated cellulose (NFC)) has also been attracting attention. In general, NFC is prepared top-down from pulp by physical and chemical treatments, and the resulting NFC is highly dispersed in water. In contrast, by optimizing the culture conditions of cellulose-synthesizing bacteria, it is possible to prepare nanofibrillated BC (NFBC: Fibnano?) from low-molecular biomass in a bottom-up manner. In collaboration with a company in Hokkaido, we have succeeded in the mass production of NFBC (Fibnano?) from molasses, a byproduct of sugar production.
Measurement Techniques for Diagnosis and Control of EUV Plasmas
Technology intended to measure and control the electron density and temperature of EUV plasma in detail using lasers.
EUV plasmas and soft X-ray plasmas can easily achieve high light intensity and are used for semiconductor lithography and material diagnostics. On the other hand, for optimization (wavelength selectivity and high efficiency), control of the electronic state (electron density and electron temperature) of the plasma is necessary, but measurement of the electronic state has not been achieved yet with conventional techniques, and the electronic state had been unknown. The feature of this technology is that it enables detailed measurement of electron density and temperature in EUV plasmas by laser scattering measurement (Thomson scattering method) using a unique spectroscopic system. This makes it possible to develop light sources based on an understanding of the electronic state, which is the root of the mechanism by which plasma emits light.
Visualization of hardness/deformation in small areas
We have enabled the in-situ observation of changes in indentation shapes and surrounding surfaces during indentation hardness tests. This will contribute to material development and the clarification of causes of accidents through the high-throughput collection of accurate data enabled by the combination of high temporal resolution of information from video recording and hardness tests.
The hardness test, a method to clarify the strength of materials from the deformation caused by local loading, is widely used based on its high simplicity and reproducibility. To obtain highly accurate stress response information while taking advantage of the simplicity of this method, we have developed in-situ hardness tests (micro-indentation) method.
To observe the surface of the specimen both inside and around the indentation through a transparent indenter during the indentation test, it is necessary to optimize the optical conditions. However, by introducing a liquid with a refractive index close to that of the transparent indenter around the indenter, we have enabled a wide range of surface observations.
Molecular-level In-situ Optical Observation of Ice Crystal Surfaces
Development of an optical microscope with atomic height resolution and in-situ observation of ice crystal surfaces
In collaboration with Olympus Engineering Corporation, we have developed an optical microscope that has atomic resolution in the height direction. We are now studying mechanisms of the growth, sublimation, and melting of ice crystals at the molecular level.
Crystals bounded by flat surfaces grow layer by layer, irrespective of materials. Therefore, to clarify the mechanisms and kinetics of crystal growth, we need to directly observe the behavior of growing ends of molecular layers (commonly called “elementary step”). However, atomic force microscopes and electron microscopes, both of which are generally used to observe solid surfaces at the molecular level, cannot be used to observe ice crystals. To overcome this difficulty, we have developed an optical microscope that can directly visualize elementary steps with the atomic/molecular height on a flat crystal surface in a non-contact, non-destructive manner. Using this microscope, we are now working on clarifying the growth mechanisms of ice crystals and the melting of ice crystal surfaces at sub-zero temperatures (called “surface melting”) at the molecular level. In addition to ice crystals, we are also conducting a wide range of research to investigate crystal surfaces at the atomic/molecular height levels.
New Crystal Material Converts Sunlight into Laser Light
New Cr, Nd co-doped crystals for high efficiency solar-pumped lasers
The Nd:CaYAlO4 crystal exhibits a wide absorption band in the visible region and a large absorption cross section. Since the energy absorbed by chromium is transferred to neodymium, it is expected to convert solar energy to laser light with high efficiency.
We have fabricated CaYAlO4 single crystals doped with chromium (Cr) and neodymium (Nd) using a technique called the floating zone melting method. By appropriately controlling the fabrication conditions, high-quality red transparent crystals were obtained (Fig. 1). The crystal has a very wide absorption range from the ultraviolet region to the visible region, and shows sufficient absorption even at the wavelength where the energy of sunlight is at its maximum (Fig. 2). We have also found that the absorption is 70 times or more that of conventional materials such as Cr and Nd:YAG. These properties are unique to the newly developed crystal and not found in existing materials. We have also demonstrated that neodymium can emit light upon excitation in the absorption band of chromium due to its fluorescence properties (Fig. 3). Based on this result, it is expected to convert solar energy into laser light with high efficiency.
Production of High-purity Sodium
Recycling of sodium resources by electrorefining
There is a sodium-sulfur rechargeable battery that is mainly used for industrial applications. In this research, I am developing a recovery process of metallic sodium from inside of used batteries, and produce high-purity sodium by electrorefining.
This research is for the development of a process of the purification of metallic sodium containing impurities by electrorefining. Metallic sodium from used sodium-sulfur batteries is used as a source material. By placing the metallic sodium in the upper left (anode) of an electrolysis cell model (Fig. 1) and applying current, the sodium ions dissolve in the electrolyte and only the sodium is deposited on the high-purity sodium (cathode) layer on the upper right. This process can be operated at 200°C or less. The high-purity sodium obtained by this electrolysis is pure enough to be used as a raw material for batteries and growth medium of semiconductor crystal. Since Japan is dependent on foreign countries for sodium resources, we believe that this technology will be widely applied in the future.
Search for Novel Spintronic Devices and Theoretical Study of the Energy Spectrum of Low-dimensional Electron Gas
Toward power-saving devices
We use condensed matter theory to study materials and structures called topological insulators and skyrmions of which the topology dominates the phenomena. At the same time, we are studying to propose and realize novel spin devices using these topological insulators and skyrmions in the process.
We are proposing spin devices that exceed the current mainstream CMOS devices in terms of performance and power, and are analyzing their performance using condensed matter theory. The main objective of this research is to create power-saving devices that provide superior performance to CMOS devices. To calculate the performance of novel spin devices, quantum field theory and relativity are used to calculate the spin conductivity and other properties. Currently, we are studying topological insulators and skyrmions. Topological insulators are bulk insulators, but spontaneous spin currents flow only on their surfaces. If successfully applied to devices, topological insulators make it possible to fabricate ultra-low power devices because the topological insulator itself is non-dissipative. Skyrmions are also a peculiar vortex generated in magnetic materials, and are expected to play the role of a switch by driving a current.Kenji Kondo Associate Professor
Semiconductor Devices That Display and Store Information Through Changes in Color and Conductivity
Can windowpanes and mirrors serve as memory devices?
We have developed new information display and storage devices by incorporating electrochromic materials, which are attracting attention as “electronic curtains,” into thin-film transistors and using the color change of colorless transparent ? black and the conductivity changes of insulator ? metal. Information can be displayed and stored on window glass and mirrors.
With the spread of IoT, the amount of information that needs to be collected and stored continues to increase as not only personal computers but also various devices are connected to the internet. Current information storage devices use only electrical resistance changes in semiconductors, but with this research, we have developed a device that can use color changes in addition to electrical resistance changes for information display and storage. A three-terminal all-solid-state thin-film transistor structure was produced on a glass or plastic substrate with source, drain, and gate electrodes consisting of a laminate of an amorphous WO3 thin film (100 nm thick)/nanoporous glass thin film (300 nm)/polycrystalline NiO thin film (50 nm) and a transparent ITO thin film (20 nm). When a positive voltage of a few volts is applied between the gate and the source, the WO3 thin film changes to a dark blue color and simultaneously becomes metal, and when a negative voltage is applied, it returns to a colorless transparent insulator.