Interface plays crucial roles for mechanical and functional properties. Despite its importance, the structure-property relationships of the interface have not been fully understood because a determination of the interface structure accompanies huge computations which is caused by the degrees of geometrical freedom of the interface. The acceleration of the interface structure searching is important for the comprehensive understanding of the structure-property relationships of the interface. Here, we applied machine learning techniques for the interface structure searching. Two methods, virtual screening and kriging, are mainly introduced. Our methods achieved considerably high efficiency and can be applied to any materials.
Kyoto Collection of Human Embryo and Fetus is a valuable collection for human developmental research during pregnancy. Although serial sections contain huge morphological information, specimens are sliced and destroyed. Three-dimensional imaging in non-destructive way are developed and now applied to the human specimens. Now, morphological changes of embryo and fetus are analyzed by geometric morphometrics as well as conservative morphometric technique using obtained images.
Development of efficient fuel cell and electrochemical cell devices to retrieve energy in a renewable manner lies in the molecular level understanding of the catalytic chemical transformation processes at surfaces and interfaces. This article demonstrates the use of operando soft x-ray photoelectron spectroscopy to correlate the chemical state of electrode and the electrochemical performance of electrochemical devices. Examples are shown for oxygen reduction reaction on the Pt cathode catalyst in proton exchange membrane fuel cells, and oxygen evolution on the IrO2 anode in water electrolyzer.
Semiconductor devices with complicated structures have been developed, and it is becoming increasingly important to understand three-dimensional (3D) structures of devices with nanometer resolution. The key to successful nanometer-scale 3D analysis is sample preparation technology and it has been highly developed. By combining or correlating multiple physical analyses, limitations of single analysis method are well covered and new information of 3D devices is obtained. Simultaneously acquired multi-signal STEM images are effective for internal structure analysis of 3D devices.
We present an overview of recent studies on the moiré superlattices in Van der Waals atomic layer materials. We first introduce typical moiré superlattices such as twisted bilayer graphene and graphene h-BN superlattice. We also argue about the Hofstadter fractal energy spectrum in magnetic fields, the strain effect and domain formation, and the graphene quasicrystals.
Frequency modulation atomic force microscopy (FM-AFM) can simultaneously detect the conservative and non-conservative force interactions between a tip and a sample, based on the resonance frequency shift (Δf) and the mechanical energy dissipation of an oscillating cantilever, respectively. Here, we outline the energy dissipation measured by FM-AFM and introduce our recent results obtained through measurement of the energy dissipation. First, surface resistances can be evaluated in non-contact using the proportional relationship between the energy dissipation due to Joule heat and Δf due to the electrostatic attractive force. Second, Si adatoms on a Si(111)-(7×7) surface, which are observed to be static by FM-AFM, can move back and force between their stable sites and their neighboring quasi-stable sites, detected by measuring of the energy dissipation.
This article provides an overview of the authors' activity on organic secondary ion mass spectrometry (organic SIMS) using ionic liquids. Ionic liquids, i.e., molten salts with a melting point less than 100℃, have negligible vapor pressures, so that they are compatible with ultra-high vacuum. They are divided into two groups : aprotic ionic liquids and protic ionic liquids. Both ionic liquids were tested as liquid matrices and as primary ion beams in organic SIMS. Protic ionic liquids proved to be effective to enhance molecular secondary ion intensities, whereas aprotic ionic liquids were not useful. Among ionic liquids, alkylammonium titrates such as propylammonium nitrate will be most promising for organic SIMS.
There have been a lot of artificial superhydrophobic surfaces, however, those are difficult to use in daily purposes because of their brittle, stiff and breakable properties. We have been reported fabrication of superhydrophobic microstructured vulcanized rubber surfaces by using silicon microstructures as mold during their vulcanization process. Furthermore, the arrangement of microstructures could be repeatedly transformed from a hexagonal to linear patterns by elongations and superhydrophobicity was kept during elongation process. In this report, we prepared other type of superhydrophobic microstructured vulcanized rubber surfaces, which can be changed surface wettability by stretching. The superhydrophobic microstructured vulcanized rubber surfaces were prepared by using a silicon microstructures as mold. After observation of surface structures and wettability by laser microscopy and water contact angle analyzer, we took high-speed photography of water droplets felled to the rubber surfaces with different elongation rates, and theoretically discussed the differences of water behaviors.
Si films including hierarchical nanodot structures were developed using ultrathin SiO2 films. Scattering bodies with various size scales are expected to scatter phonons with various wavelengths. This idea is important for reduction of thermal conductivity because phonon, that is boson, with various wavelengths, can contribute to the heat transport. Here, in Si films including Si nanodot structures, the nanodots with various sizes reduced the thermal conductivity effectively in addition to increase of dopant activation rates. Furthermore, highly-doped Si films including Ge nanodots that have atomic scale and nanoscale phonon scattering bodies exhibited drastically-reduced thermal conductivity. This drastic reduction of thermal conductivity came from hierarchical structures that include nanodot structures working as strong phonon scattering bodies. This gives the guideline of control of phonon and carrier transport using nanostructures for high performance thermoelectric materials.
Semiconductor cleaning is a very important process in integrated circuit manufacturing, and the removal of high dose ion implanted photoresist is a big challenge in semiconductor cleaning owing to their carbonized crust layer generated on and near the surface of the photoresist layer. Microbubbles are a promising candidate in single wafer spin cleaning process for the removal of the crust generated photoresist without any substrate loss. And the bubbles are gas bodies less than 50 micrometer in diameter and shrink underwater due to the rapid dissolution of the interior gas. It has been demonstrated that the bubbles can generate free radicals during the collapsing process under water through the dispersion of the elevated energy accumulated as the surface electricity during the collapsing process of microbubble. In this article the author introduces the fundamental properties of microbubble and their several examples relating to semiconductor cleaning.
This report is a personal research history of the author. The author engaged in the extreme high vacuum project in 1988. Before that time, the research field of the author was limited to the surface finishing of metals. However, since 1988 the author has been stimulated by the intense communication with researchers of different fields, and the author’s research field has been expanded even to the standardization of surface analyses. The author has been involved in the activities of Japan Vacuum Society and Surface Science Society of Japan since 1980’s. Through these activities in societies, the author could get to know many nice researchers, and these researchers help the author to challenge new research fields. Extreme high vacuum is one of the bridges between vacuum and surface. The author believes there are many bridges between vacuum and surface, and communications through these bridges will make the society more active.