We report a selective metal deposition method applicable to metal pattern formation by maskless deposition. The core phenomenon of selective metal deposition is the desorption of metal atoms from soft surfaces. However, it did not attain to the desorption of Ag and Cu, which are commonly used in the electronics field. Recently, we discovered that metals such as Ag can be desorbed from the surface of a specific organic fluorine film with high efficiency. We have clarified that one of the important factors causing the detachment is the low-dispersion component of the surface free energy. Furthermore, by comparing water repellents and mold release agents, which are typical organic fluorine materials, we have shown that surface flexibility is important. This phenomenon can be applied not only to maskless vacuum deposition for forming various metal patterns, but also to various applications in vacuum deposition.

Molecular hydrogen (H₂) has nuclear spin isomers: ortho-H₂ and para-H₂. Under the isolated condition, the nuclear spin conversion (NSC) between these isomers is forbidden. The ortho-to-para ratio, OPR, of H₂ is important in chemistry and physics of interstellar media. The OPR in space has been considered to evolve only via the gas phase reactions with proton and hydrogen atoms. Because interstellar H₂ is produced predominantly on the surface of cosmic dust and gaseous H₂ molecules inevitably collide with dust, the NSC process on the surface of cosmic dust should be quantitatively qualified to know the evolution of OPR. Recently, we revealed that the H₂ NSC occurs on cosmic dust analogs within laboratory timescale. In this article, we introduce the methods for observing NSC processes, the NSC time constants determined for the surfaces of amorphous solid water, amorphous-Mg₂SiO₄, and diamond-like carbon at low temperatures, and implication of the results to astrophysics.

BaSi₂ has ideal optical properties for solar cell applications and can potentially realize solar cells with higher efficiency and lower cost than the mainstream crystalline Si solar cells. The close-spaced evaporation technique allows epitaxial growth of BaSi₂ films on Si substrates with scalability to large areas. The technique itself and the properties of the BaSi₂ films are reviewed in this article. Using a BaAl₄–Ni source ground in a mortar and pestle, BaSi₂ films with (001) preferred orientation are grown on Si(100) at 1000℃. Such a high temperature growth leads to film cracking. Mechanical activation of BaAl₄–Ni by ball milling lowers the BaSi₂ film formation temperature down to 700℃, resulting in crack-free films. The preferred orientation changes from (001) to (100). The crack-free BaSi₂ films have low electron concentration around 10¹⁶ cm^－3 and show clear photoconduction, suggesting potential availability for solar cells.

Two-dimensional or three-dimensional porous polymer known as the covalent organic framework (COF) has been gathering attention due to its unique properties such as low density, high stability, and tunable pore characteristics. The reported methods to synthesize practical COF films have inherent problems because they are liquid phase reactions. We have developed a new method to synthesize the COF film by alternating vapor deposition polymerization. The films annealed at 400℃ for 10 minutes had a pore network structure with a diameter of 2.4–3.6 nm. From the gas permeation experiments, the COF films exhibited CO₂ and N₂ separation performances of 4.6 at the transmembrane pressure of 10⁵ Pa. Numerical analysis and quantum chemical calculation suggest that the COF was more permeable to CO₂ than N₂ due to its greater affinity for CO₂ compared to that for N₂.

EXAFS is powerful to obtain the structure information around the X-ray absorbing atom at the atomic size level. EXAFS is usually analyzed by the curve fitting method, one of the least square methods to optimize structure parameters. However, the curve fitting method demands the experience of scientists when they analyze the EXAFS of materials with complex structures. In particular, the following two items make the analysis difficult especially for beginners ; 1. the dependence on the initial selection of the fitting parameters, 2. fitting errors caused by their correlation. We developed a new method, called as Constrained Thorough Search (CTS) method to solve these problems. The CTS method searches the whole parameter space under constrained conditions to extract the structure candidates. We describe the details of the CTS method with their results. We also applied the machine learning method to CTS results which allows us to conduct the analysis more objectively.

Single-molecule junctions (SMJs) have attracted wide attention due to their unique electronic property originating from their structure, i.e. single molecule connected to the electrodes at both ends. Although the junction structure has significant effects on the electronic property of the SMJs, the experimental method to define the geometry of the bridged molecule is limited. Recently, we have succeeded in the observation of surface-enhanced Raman scattering (SERS) spectroscopy in combination with the current-voltage (I–V) response measurement, revealing the junction structure of SMJs. The I–V response obtained by the combination measurement provides the electronic structure of the molecule fluctuated by the connection to the metal electrodes, allowing the analysis of the effect of the charge transfer on the SERS spectra. The strong electronic coupling between metal and molecule enhances the charge transfer resonance and it triggered the excitation of the “Raman silent mode” in the bulk state. Therefore, we have detected the unique SERS spectra in SMJs and revealed the contribution of the charge transfer effects on the SERS spectra at the single-molecule level.

Vanadium dioxide (VO₂) thin films exhibit a metal–insulator transition (MIT) near room temperature with sensitivity to the lattice strain. MIT property has been tuned by W-doping, fabrication of nanowires, etc. In addition to these methods, use of step and terrace structures could be a prospective candidate to control the MIT property since VO₂ is sensitive to the lattice strain at the interface between thin films and substrates. In this study, VO₂/TiO₂ microwires were fabricated following the thin film growth to investigate the in-plane crystal orientation dependence of the MIT property. The VO₂/TiO₂ microwires with step and terrace structures exhibited a more significant MIT anisotropy, which is promising for strain engineering in device applications.