Research

The world’s first multi-quantum beam HVEM (left)
In 2014, we added an optical system that allows the use of multiple lasers, and developed a multi-quantum beam HVEM that allows in-situ observation at the atomic level under irradiation by multi-quantum beams, including ion, laser and electron beams. We are currently developing an in-situ spectroscopy system.

Nanocrystal growth by UV irradiation (right)
We have succeeded in growing ZnO nanocrystals by irradiating submerged plasma-treated Zn with UV light. We are now promoting research on the growth mechanism and its application.
Scientific Report, 5, 11429(2015), AIP Advances, 7(2017) pp. 035220, Other reference: Nano Letters, 17(2017) pp. 2088-2093

Research

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.

Research

Until now, chemical reaction phenomena in thermo-fluid (CFD) analysis have been modeled simply by assuming an infinitely fast reaction or an overall reaction model consisting of a few chemical species and reaction equations due to computational load and lack of analysis techniques. On the other hand, when the interaction between chemical reactions and fluid phenomena is important, such as in the case of unsteady phenomenon prediction like the ignition timing of automobile engines or ultra-dilute combustion under extreme conditions, it is difficult to apply simple models. Our research group has solved the problem of applying detailed reaction mechanisms to CFD analysis. The proposed method consists of a time integration method (ERENA) that can significantly reduce the calculation time of chemical reaction equations, and a species bundling technique that combines similar chemical species. Depending on the conditions, the proposed method can be tens to hundreds of times faster than the conventionally used methods while maintaining equivalent accuracy.

Research

The significant drag reduction in turbulent channels due to the addition of a small amount of long-chain polymers or surfactants that form rod micelles in water, is known as Toms effect. A model that simulates polymers with small dumbbell-shaped elements was constructed, and direct numerical simulation (DNS) of turbulent flow in a two-dimensional channel was performed using this model to reproduce Toms effect. It was shown that the discrete element has two mechanisms: one is a resistance reduction mechanism due to the longitudinal vortex damping, and the other is a resistance increasing mechanism due to the additional stress near the wall. Furthermore, by adding the effect of cutting the element to which a strong force is applied, we were able to reproduce the feature that drag reduction occurs in a specific Reynolds number range.

Research

We invite, select and implement proposals for the effective use of stable isotope imaging technology, which is a special feature of the isotope microscope system, to expand it to industrial innovation.
Upon hearing the word, “isotopes,” the concept of “age measurement” immediately comes to mind. Actually, until now, isotope microscopes have been used to analyze isotope ratios, primarily in minerals and other areas of space science. This is a result obtained by observing the as-is cross-section of the obtained sample. However, by changing the concept of the measurement method, we can expand the use of isotope microscopes to industrial application. In other words, by actively doping a target sample with an isotope element, rather than observing it “as such,” it becomes possible to measure the desired imaging we were unable to see before. The use of stable rather than radioactive isotopes also allows us to work safely.

Research

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.

Research

Since the amount of data handled during image processing is generally huge, it is essential to optimize the system as a whole by combining hardware and software. In this laboratory, we are investigating the configuration of image processing systems by studying image processing algorithms and their implementations complementarily. One of the results of our research is real-time adaptive brightness correction of video images based on the Retinex theory (Fig. 1), which can adaptively correct the brightness of video images taken under conditions of large changes in illumination, such as backlighting, in real time. We are also working on high-quality image smoothing (Fig. 2) based on cost optimization, which is expected to be applied to image processing such as photo illustration, pre-processing of various image processes, brightness correction, and detail enhancement.

Research

We are proposing a system (e.g., planning, modeling and evaluation based on experiments and field studies) that can contribute to both the environment and regional development (economy) by linking energy recovered from biomass (e.g., food waste, sewage sludge, livestock manure, forest residues, and rice straw) through combustion and methane fermentation with local energy consumers (e.g., public facilities, nursing and welfare facilities, agricultural facilities such as greenhouses and food factories). Furthermore, by obtaining cooperation from private companies, we are conducting research on creation of community through biomass utilization in collaboration with the endowed laboratory of biomass community planning (Visiting Professor Toru Furuichi, Specially Appointed Assistant Professor Satoru Ochiai, https://smcs.eng.hokudai.ac.jp/bio-com-p.html).

Research

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.

Research

Plasmas generated in liquid are of great interest in the fields of nanotechnology, environmental engineering and medical engineering, but the need for high voltage to generate the plasma can be an obstacle. Meanwhile, in the field of ultrasonic engineering, it is known that the interior of a bubble becomes plasma at the same time as the collapse of acoustic cavitation. Using a very simple method of inserting a perforated metal plate into a liquid where ultrasonic waves are applied, we have succeeded in localizing and efficiently generating acoustic cavitation, which is difficult to fix in position. This has been valued as a unique method of generating plasma in liquid without using high voltage. Currently, we are working to clarify the mechanism of this method and to prepare guidelines for the design of a large-scale device. In the future, we hope to develop various new plasma application technologies.

Research

Thermoelectric conversion has been attracting attention as a technology to recycle waste heat. Metal chalcogenides are known as thermoelectric materials, but they have thermal and chemical stability and toxicity issues. Layered cobalt oxides are stable at high temperatures and in air, but have the problems that thermal conductivity is high and conversion performance is low. The research group considered the strategy shown in Fig. 1 to reduce the thermal conductivity of layered cobalt oxide AxCoO2. Figure 2 summarizes the thermoelectric properties in the direction parallel to the layers of Ax-substituted AxCoO2 thin films measured at room temperature. The thermal conductivity shows a monotonically decreasing trend with increasing Ax atomic weight. The room temperature thermoelectric figure of merit of Ba1/3CoO2 is 0.11. The figure of merit ZT increases with increasing temperature. By further enhancing the thermoelectric conversion performance, it is expected to realize stable and practical thermoelectric conversion materials.

Research

Based on our previous research results, we have discovered that when a droplet hits a solid surface in a condensable gas (not air), splashing is suppressed and a thin liquid film (lamella) spreads on the solid surface at high speed. Since the high-speed lamellae may generate a strong fluid shear force, it seemed possible to use a mixed jet of steam and water to realize an environmentally friendly cleaning method.
Based on our previous research results, we have confirmed that this cleaning method, which uses only water and steam, can achieve the specified cleaning performance for ultra-precision cleaning required in the manufacturing processes of semiconductors, LEDs, and solar cells. This cleaning method is also safe both for the human body and the environment, because it uses only water and steam instead of detergents or other chemicals that are harmful to the human body.

Research

It is expected that superomniphobic surfaces, which do not get wet with water or oil, will possess antifouling and self-cleaning properties. In this study, we have realized a superomniphobic surface that does not only repel water but also octane and other liquids with a surface tension as low as 20 mN m-1, by using a simple wet process for aluminum, which is a practical metal material. This process can also be applied to aluminum foil, which can be used as an antifouling surface in various places. It can also be used as a filter to separate oil and water by controlling its wettability using aluminum mesh.

Research

The introduction of fluorine atoms into organic compounds is very important in the fields of medicine, agrochemicals, and functional materials. There is a method of synthesizing fluorine-containing organic compounds by using fluorine-containing building blocks, but such compounds are still expensive and limited in quantity, and there is a high need for research and development. In this study, we succeeded in synthesizing fluorine-containing aromatic carboxylic acids with various functional groups from readily available fluorine-containing aromatic compounds and carbon dioxide, and achieved good yields using the organic electrolysis method. The fluorine-containing aromatic carboxylic acids synthesized in this study include a variety of new compounds that are difficult to synthesize by conventional methods, and are expected to be used as promising new fluorine-containing building blocks for the synthesis of pharmaceuticals, agrochemicals, and highly functional materials.

Research

Visualization of acoustic wave propagation is extremely useful in the evaluation of physical properties and the design, fabrication and evaluation of functional devices using acoustic waves. For this purpose, we excite surface acoustic waves by irradiating the sample with an ultrashort optical pulse of subpicosecond duration (pump light), and observe their propagation with delayed optical pulse (probe light). Time-resolved two-dimensional images of the acoustic waves are obtained by scanning the delay time and the irradiation position of the probe light. The time resolution is in picoseconds, the spatial resolution is 1μm, and the frequency range is in GHz. Since this method uses a periodic optical pulse train, it was previously only possible to excite and detect acoustic waves at integer multiples of the repetition rate. However, with the newly developed technique, we have realized the excitation and detection of acoustic waves of any frequency. By developing this technique, we have also achieved image vibrations that are completely asynchronous to the repetition frequency of the optical pulse, thereby expanding the range of applications.

Research

We have succeeded in obtaining titanium dioxide thin film on a practical metal substrate such as Cu, Al, Zn and Fe by electrolysis from an aqueous solution containing TiF62- within only a few seconds. The obtained titanium dioxide thin film is anatase crystalline and shows photocatalytic activity without heat treatment. The obtained titanium dioxide thin film is anatase crystalline and shows photocatalytic activity without heat treatment. We have confirmed that it has excellent properties such as decomposition of organic contaminants on the surface by UV irradiation and superhydrophilicity. Since the titanium dioxide film is doped with substrate elements, the development of new functions such as visible light responsiveness can be expected. It can also be deposited on a transparent conductive substrate.

Research

EDLCs are electronic devices that are attracting attention as next-generation storage batteries that can replace rechargeable batteries such as Li-ion batteries. The parts called electrodes and separators in EDLCs are made from polymeric materials, so we are conducting research on replacing these polymers with lignin, a major component of woody biomass. By forming lignin into microfibers through electrospinning and converting them into active carbon fibers, we have succeeded in producing the large surface area required for electrode materials. This has led to the production of electrodes with high energy and power densities. In addition, by converting lignin into a flexible polyester film, it became possible to prepare a material that exhibits the same performance as conventional separators. We are currently endeavoring to further improve the performance.

Research