In materials research, attention is attracted by so-called materials informatics, which conducts research and development typically using machine learning of experimental databases or large data obtained by computer simulations. In Japan, research is proceeding with projects such as JST PRESTO and NIMS MI^2I. In this lecture, we focus on the results at PRESTO and outline the current situation in this research field.

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Theoretical prediction of defect properties, as well as fundamental bulk properties, is a key ingredient for the computational discovery of novel materials. In this talk, I will report systematic prediction of the fundamental and defect properties of semiconductors using first-principles calculations and the exploration of novel materials based on the computational data, with an emphasis on nitride semiconductors.

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Investigation of the atomic and electronic structure of interface or surface accompanies great difficulties due to their structural complexity. In this study, we combined theoretical calculation, atomic resolution analysis with machine learning. In particular, we will talk about 1) acceleration of interface structure searching by machine learning and 2) spectrum interpretation by machine learning in the presentation.

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Surface X-ray diffraction technique is a non-destructive, non-contact method to study surface/interface structure in 10pm resolution. Its application to wide variety of surfaces/interfaces is, however, hampered by the difficulty of the analysis. We have developed a Bayesian inference method to obtain the structural models that are physically reasonable as well as reproduce the diffraction data. The performance of the new method is demonstrated on epitaxial interface of transition metal oxides.

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Various methods are used for the measurements in surface science. However, many parameters (measurement time and measurement points, etc.) used in these measurements are often determined based on the experience and intuition of experts. We performed the research on the optimization of surface science measurement method using machine learning. In the talk, we discuss the optimization of X-ray absorption spectrum measurement using a technique called the adaptive design of experiments.

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Material Informatics is one of the central subject in materials science today. Coercivity of magnetic material is an important property determining power generation efficiency of motors; however, the analytical methodology has not been perfectly developed.

Here, we applied “Persistent Homology” to the magnetic domain structure to describe macroscopic magnetic properties. Persistent Homology is a powerful methodology for quantitative evaluation of topological feature in structural data. Moreover, it provides us the inverse analysis from macroscopic property to structural data in the combination with machine learning. We demonstrate Persistent Homology analysis on magnetic domain structure, and examine the validity as a descriptor.

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Information of material surface (topography, conductivity, composition) has been extracted by controlling secondary-electron detection using low-voltage SEM equipped with in-lens and out-lens type electron detectors. We will discuss the relationship between experimental conditions including detector selection and contrasts appeared in SEM images in terms of kinetic energy and take-off angle of detected electrons.

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Standard operating procedures of surface analysis techniques were developed several decades ago, and are unfit for nanomaterial samples. In this talk, we will introduce a virtual substrate method to extract pure nanomaterial information from overwhelmingly strong underlying substrate signals. The virtual substrate method uses a secondary electron spectrum as a probe instead of a conventional monochromatic electron beam, meaning core-level signals are no longer the only choice to characterize materials. The developed virtual substrate method will generate broad interest from numerous fields that use surface analysis techniques for research, manufacture and quality control.

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We have developed low energy secondary electron (SE) detector for outlens-type scanning electron microscope and named it as fountain detector (FD). Using this FD, we observed pn-junctions in SiC. p-region is darker than n-region in SE images lower than 2 eV, while brighter in those images higher than 2 eV. The comparison of SE spectra indicates the SE spectrum of p-region shifts about 2 eV higher than that of n-region. This FD may open up the new surface potential imaging using low energy SEs.

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The electron spectra for the single crystalline Al and Cu are measured using the CMA analyzer in order to explain the fine structure of the energy distribution of the secondary electron from the solids. The fine structure of the secondary electron of Al as the NFE metal does not depend on the crystal orientation, because the plasmon contributes to the fine structure. The fine structure for Cu depends on the crystal orientation. It strongly suggests that the emission of the secondary electron for Cu results from the electron excited the unoccupied state after the inter band transition.

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We have calculated inelastic mean free paths (IMFPs) for 42 inorganic compounds for electron energies from 50 eV to 200 keV. These calculations were made with energy-loss functions (ELFs) obtained from measured optical constants for 15 compounds while calculated ELFs were utilized for the remaining 27 compounds.Our calculated IMFPs could be fitted to a modified form of the relativistic Bethe equation for inelastic scattering of electrons in matter for energies from 50 eV to 200 keV. The IMFPs were also compared with a relativistic version of our predictive Tanuma-Powell-Penn (TPP-2M) equation. The average RMS deviation in these comparisons was 10.7 % for energies between 50 eV and 200 keV.

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[in Japanese]

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In Materials Data Platform Center, NIMS, we have been beginning to convert and collect analysis data for constructing the material data bank. By the "Scheme on Read" method, which makes no request on the data format on the raw data generation side, we structure the conversion data as a group of information excluding the constraint condition as much as possible so that it can be used for expressing a wide range of analysis data. In the presentation, we will introduce examples of application to actual analysis data.

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The application of a tunnel junction is studied for spin injection from ferromagnetic metal into semiconductor, and the spin injection into Si is achieved at room temperature by an MgO tunnel barrier. The author has studied the surface potential of MgO/Si and found the decrease in the strength of the interface dipole by annealing so far. In this study, relations with the spin injection properties have been studied and a design of the tunnel barriers has been discussed.

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The quantum dot (QD) films with blue LED show better luminescence properties than the white LED alone, and improve the color reproducibility of LCDs. Our early development QD films had the problem that luminescence properties deteriorated after reliability test under high temperature and high humidity. In this report, we will discuss the factors of optical properties deterioration from viewpoints of the chemical composition, the crystal structure, a dispersion of the QD particles.

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In the fabrication of organic semiconductor thin films by the vacuum evaporation, thin film structures are greatly influenced by elementary processes in the initial stage of the thin film growth, such as adsorption, desorption and diffusion. In this work, we performed an in-situ measurement during pentacene thin film growth using a quartz crystal microbalance, which is non-destructive and highly accurate measurement of adsorption amount of molecules. By analyzing results, the mean stay time of pentacene molecules on a substrate, which is an important physical parameter in thin film growth, was successfully estimated quantitatively.

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We have investigated the fundamental properties of graphene-assisted chemical etching, which is preferential etching of a Ge surface in contact with single sheets of reduced graphene oxide (rGO) in water. In this study, in order to realize a higher etching rate, we unveiled the dependence of the etching rate on solution temperatures. The Arrhenius plot from the obtained results revealed that the activation energy of etching becomes lower on a Ge surface in contact with rGO sheets than on a Ge surface just immersed in water.

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Photochromic diarylethene amorphous films exhibit selective metal-vapor deposition, in which metal-vapor deposition property is different depending on its isomerization state. This is originated in a large change in the glass transition temperature Tg due to photo isomerization, and metal species such as Mg, Pb do not deposit on the low Tg surface. This function can be applied to prepare electronics and photonics devices having fine metal patterns using laser scanning and maskless evaporation.

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Plasma-wall interactions in fusion devices is briefly introduced. In a fusion reactor, a high temperature and high density plasma is confined in so-called closed magnetic surfaces. A relatively low temperature plasma exists outside the closed magnetic surfaces, and that interacts with surfaces of vacuum vessel wall and in-vessel components. By the interactions, erosion of materials of the surfaces, and retention and recycling of plasma particles in and from the surfaces take place, and they affect the fusion plasma. An interesting topic of plasma-wall interaction is dust properties in fusion devices. That is also introduced in this talk.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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In the recent years, 2D materials have drawing increasing attention due to its favorable electrical properties and intriguing physical properties. Among the various fabrication technique, we employ sputtering deposition. It has been revealed that the film quality heavily depends on the substrate surface condition, deposition environment, and the form of the film itself. We have been reporting on the film quality dependence on each of those parameters for transition metal dichalcogenides in particular. We will report and discuss on those progresses we have made.

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[in Japanese]

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We report CVD growth of MoS₂ and the analysis of the structure and defects of grown materials. MoS₂ nanowires can be grown by using chemically synthesized FeO nanoparticles as catalysts. The chirality from TEM observation was armchair. It was found that the protrusion of FeO nanoparticles plays an important role for the nanotube growth. We also report that the defects in the monolayers can be controlled by annealing in various environment.

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We have investigated the growth mechanism of 2D layered materials like graphene and their heterostructures mainly using low-energy electron microscopy (LEEM). In this presentation, we review our research with an emphasis on in-situ LEEM observations of graphene segregation on metal surfaces.

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Chemical vapor deposition (CVD) of graphene is the most promising method for fabricating high quality and large area specimens. Since the optimization of growth is usually based on post growth observation, an enormous number of experiments would be necessary. We have developed a thermal emission microscope (Radiation-mode optical microscopy) which can observe the growth of graphene in real time. This method allows us to instantaneously know the influence of various parameters on growth. On the basis of real-time observation of graphene growth, I will discuss the growth mechanism and introduce the examples to control the growth.

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Diversity has not yet been considered an important factor in science and technology. Recently, it has been clarified that gender difference is a key factor in economic value of the patents and success of the entrepreneurs in Japan, leading that diversity is an essential determinant for research and development of science and technology, and societal sustainability. Furthermore, redefinition of gender equality, which can create societal benefits for all the people, will be shown.

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Surface Science stands together with vacuum technology. Creating a clean surface and applying TPD for characterizing surface species are not only the necessity but without utilizing deferential pumping techniques, electronic state of surface at solid-liquid or liquid-liquid interfaces is not possible. For studying single-molecule spectroscopy, UHV and low temperature condition are necessary and further for the study of spin state of surface species, applying magnetic field become crucial. I will present some results only obtainable under such extreme conditions.

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We investigated adsorption configurations of organic molecules using atomic force microscopy (AFM) imaging and force spectroscopy. A conventional cantilever-based AFM revealed structures of fullerene and pentacene adsorbed on anatase titanium dioxide. An AFM with a sensor based on a quatz resonator was successfully used to track structural transformation of porphycene molecules adsorbed on silver and NaCl thin films. We also discuss advantages and disadvantages of above two methods.

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Extremely dense, random single-walled carbon nanotube (SWNT) and polyoxometalate (POM) network molecular neuromorphic devices generats spontaneous spikes similar to nerve impulses of neurons. A simulation calculations of the random molecular network model complexed with POM molecules, which are able to store electric charges, replicated spikes generated from the random molecular network. Recentely, we observed that single POM molecule exhibits a conductance swiching due to the multi electric strage. The SWNT/POM network would very likely become a component of reservoir computing that is anticipated as next-generation artificial intelligence devices.

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[in Japanese]

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In fusion devices, retained hydrogen by plasma material interactions was observed. Released of hydrogen, which was called wall recycling, and permeations occur. For analyses of hydrogen for these specimens, total amounts and depth profiles are required. In this talk, hydrogen analyses on specimens after plasma exposures, and these issues are presented.

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When X-rays are irradiated, photoelectrons are emitted. In the process of photoelectron emission and propagation, the potential change yields plasmon, then photoelectrons lose energy. The multiple scattering method have been used for handling the behavior of photoelectrons without approximation. Based on this method, we report the analysis of plasmon peaks by X ray irradiation.

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A strongly correlated electron material NdNiO₃ exhibits the drastic changes in conductivity owing to metal-insulator transition (MIT). Since the discovery of phase separation during the IMT, nanostructuring is effective to confine and understand a nanoscale electric domain MIT property. We produced the NdNiO₃ nanowires with 50-100 nm width and investigated their electric transport properties.

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[in Japanese]

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The phase-2 commissioning of the SuperKEKB accelerator, a large electron-positron circular collider in KEK, has started since February, 2018. The vacuum system of the new positron damping ring (DR) and the main ring (MR) with a new particle detector has been working well for the most part. We will report the present status of the SuperKEKB vacuum system, especially focusing on the operational status during the Phase-2 commissioning, will be presented in detail.

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When the pump-down time by the dry vacuum pump is predicted, the performance curve (inlet pressure vs. pumping performance), which is measured prior to the pump-down time calculation, is used for calculation. However, the potential performance fluctuation might not be figured out from the performance curve, because the gas flow rate flown into the pump dynamically changes during the chamber pump-down from atmospheric pressure. This activity is for the accuracy improvement of chamber pump-down time prediction with the assumed dynamic performance fluctuation.

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The pressure p is proportional to the refractive index (n_gas-1). The refractive index can be measured from the resonance frequency of the laser using a Fabry-Perot resonator. Because it is based on frequency measurement, wide range pressure measurement is possible with small uncertainty. In this research, we developed a measurement system for the pressure range from 1 Pa to 100 kPa. In this presentation we report the principle of measurement, the outline of the experimental system, and the measured linearity between the refractive index (n_gas-1) and the pressure p.

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In 2014, ISO 3529-3 “Vacuum technology -- Vocabulary -- Part 3: Total and partial pressure vacuum gauges” was revised after about 30 years from the publication of its 1^st edition. A committee of JVSS on the standard and a committee of JVIA on the standard made a committee to revise JIS Z 8126-3, which is Japanese localized version of ISO 3529-3. In this paper, the revised JIS 8126-3 is briefly introduced with several issues related to the Japanese localization.

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[in Japanese]

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We developed a non-evaporable getter (NEG) pump in which oxygen free Pd/Ti was deposited on the inner surface of a vacuum vessel consisting of ICF 203 flange, pipe, bottom plate, nine partition plates and support plate. The present NEG pump can be activated by baking at 150 °C for 12 h. The initial pumping speed was about 670 L/s for H₂ and about 880 L/s for CO. In addition, it was confirmed that the pumping speed did not decrease even if air vent and activation were repeated nine times.

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Non-evaporable getter (NEG) coating is widely used in accelerators for maintaining ultrahigh vacuum. We developed a new oxygen-free Pd/Ti NEG coating, whose pumping speed does not decline even after repeated vent-activation cycles with an activation temperature of about 150°C. However, it is known that the pumping speed is suppressed when carbon contaminants cover the Pd film surface. Here, we report that carbon contamination can be removed by baking under O₂ pressure 1.3×10^-4 Pa, and the pumping speed can be improved several times.

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Pd or Pd/Ti thin films was deposited on the inner surface of a stainless steel vacuum vessel by UHV sublimation method, and the total and partial pressure curves were measured for non-coated and Pd-coated vessels. As a result, it was found that the pressure of Pd-coated vessel was one digit lower than that of non-coated vessel, the same result is obtained even when nitrogen vent is repeated, and in the case of Pd-coated vessel water can be pumped more quickly. The Pd/Ti-coated vessel reached the pressure range of 10^-8 Pa after 3 hours baking at 150 °C .

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[in Japanese]

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