Diradical character is important for investigating and predicting the functions of singlet biradical molecules. Singlet biradical molecules possess many unique properties, and their immobilisation by surfaces has been extensively studied for applications in devices, such as quantum computers, single-molecule magnets, single-atom catalysts, organic batteries, and organic superconductivity devices. Recently, an estimation scheme of diradical character from the calculated results of density functional theory with plane-wave basis (DFT/plane-wave), which is a general method for calculating the electronic structures of surfaces, was developed by our research group. This scheme enables us to investigate the diradical character of the open-shell structure stabilised by the surfaces. In this study, DFT/plane-wave calculations for s-indaceno[1,2,3-cd;5,6,7-c’d’]diphenalene molecules, whose diradical character was experimentally observed, were performed. Using the developed scheme, it was verified whether the diradical character was modulated by the interaction with the MgO(001) surface. The calculated results showed that the diradical character increased as the distance from the surface decreased, although the enhancement effect of the surface was inhibited by the steric hindrance of the substituents.
In this study, the substrate potential dependence of the film structures and optical characteristics of hydrogenated amorphous silicon (a-Si:H) prepared by reactive sputtering was investigated for application in short-wave near-infrared band pass filters (BPFs). During direct current (DC) sputtering, the substrate was charged to a negative potential, which was further increased by applying an RF bias. When the negative potential was large owing to the bias, the surface of the film became smooth owing to the ion bombardment. However, the refractive indices of the films decreased as the Si—H2 bonds increased. When radio frequency (RF) sputtering was used, the acceleration voltage of the ions decreased to 1/3; thus, structural relaxation was promoted. Consequently, a-Si:H with a high refractive index, low optical absorption, and high thermal durability, which are suitable for a narrow BPF, was obtained. The deterioration after annealing of the characteristics of the BPF using a-Si:H prepared by RF sputtering was reduced by half compared with DC sputtering.
The energy-loss spectra of the specular reflection electron beam from the Si(111)7 × 7 surface were measured under one beam condition and ❬112❭ incident azimuth using a novel energy-filtered reflection high-energy electron diffraction apparatus with high spatial and glancing angle resolutions. All measured spectra were precisely peak resolved based on the Poisson distribution, and the mean number of excitations for the main surface plasmon and weak bulk plasmon was obtained. The mean number of surface plasmon excitation was proportional to 1/sinθ with respect to the glancing angle θ, ∼70% of Lucas' theoretical value. The surface plasmon excitation showed a moderate increase under Bragg reflection conditions, correlated with the integrated intensity of the wavefield in vacuum including the subsurface. Conversely, the mean number of bulk plasmon excitation showed an inverse behavior to the intensity of the specular reflection. The wavefield in the crystal was localized on the vertical bonds between the Si bilayers when the bulk plasmon increased. For ❬112❭ incidence, large anomalous increase was observed both in surface and bulk plasmon excitations at a glancing angle of θ = 4.2°. At this angle, the specular spot was located quite close to the intersection of several Kikuchi lines, with very weak specular reflection intensity, suggesting that the Kikuchi electrons had a strong influence on the energy-loss spectrum. The Kikuchi lines were formed by inelastic scattering inside the crystal, consistent with their contribution to the increase in the bulk plasmon excitation, but they did not explain the anomalous enhancement of surface plasmons as well. The relationship between Kikuchi lines and surface plasmon excitation enhancement is still a work in progress.
Bismuth ferrite (BiFeO3) was synthesized using hydrothermal method in two different size autoclaves (100- and 200-mL capacities). By fixing conditions including filling factor, quantity of precursors, KOH concentration, reaction temperature, and duration time, the properties of the resulting products were compared. In this work, different analytical techniques were applied to identify the phase evolution and morphology of the samples such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The results demonstrated that the crystalline phases and the particle sizes were different when the dimension of the autoclave was greatly changed. Considering the reaction temperature and the autoclave size, we suggested that the heat transfer from the autoclave into the solution might be delayed and it may be the reason why the Bi25FeO40 phase was mainly obtained when the samples were prepared at 160°C for 6 h in the 200-mL autoclave.
Polyunsaturated lipids are one of major components in cell membranes, but have attracted less interests compared to lipids with saturated or monosaturated acyl chains. A recent study reported that polyunsaturated phosphatidylethanolamine (PE) induces the non-raft domain formation in lipid bilayers comprising fluid phosphatidylcholine (PC) and cholesterol (Chol) via the segregation of polyunsaturated PE. In this study, we investigated the effects of polyunsaturated PC on the non-raft domain formation. We prepared supported lipid bilayers (SLBs) comprising polyunsaturated PC, monounsaturated PC (POPC), and Chol. Observation by fluorescence microscopy and atomic force microscopy showed that polyunsaturated PCs caused the domain formation, depending on their concentration and the degree of unsaturation. However, their effectivity was less than polyunsaturated PEs. Intermolecular interaction at the hydrophobic part induced the segregation of polyunsaturated PC from the Chol-containing region, although competing with the umbrella effect due to the hydrophilic headgroup of PC which favors the association with Chol.
Optical second-harmonic generation (SHG) in self-assembled ampholytic mega-molecule polysaccharide sacran is an interesting phenomenon but its origin has not been clarified. SHG-active sacran aggregates in dried cast films made from ultrasonicated 0.5 wt% sacran aqueous solutions were studied at microscale using the scanning electron microscope and the energy dispersive X-ray technology. Hexagonal morphology was observed frequently with the size of a few to tens of micrometers. The calcium density was higher in the area showing the SHG signals. In sum-frequency generation spectra of the SHG-active sacran aggregates, vibrational modes of functional groups such as CH3, CH2, and −COOH of the sacran molecules and OH of the water molecules were identified. The structure of the SHG-active sacran aggregates was modeled from the observed facts.
Methods for removing the surface oxide film have been investigated to make a titanium vacuum chamber itself act as a getter pump. The build-up test of the titanium chamber has been performed to investigate the effect of baking. The result showed that the higher the baking temperature the lower the pressure rise during the build-up. Especially the baking at 400°C, the pressure kept less than 10-3 Pa after 2 h of build-up. The lower pressure rise in the build-up test of the vacuum-fired titanium chamber suggests that once the surface oxide has been removed by the high temperature such as 850°C in the high vacuum furnace, the surface oxide film can be removed more easily because the regenerated oxide film is thinner than before. The results of the X-ray photoelectron spectroscopy supported these facts; namely, it is shown by the photoelectron spectrum of Ti 2p near the surface that the titanium oxide peak intensity decreases while that of the metal titanium increases by the 400°C baking; the O 1s peak intensity becomes smaller near the surface while that in the bulk becomes larger by the 400°C baking, which implies the thermal diffusion of the oxygen to the bulk; the O 1s peak intensity is reduced near the surface by the vacuum firing. The effect of the removal of the surface oxide film by the sputtering has also been investigated by a throughput method. After sputtering the surface of the titanium chamber, the pressure in the titanium chamber has become lower than that in the chamber of the other side of the orifice, which is pumped by the turbomolecular pump. A large pumping speed was obtained for CO, O2, and CO2. Furthermore, the titanium chamber, which is non-evaporable getter (NEG) coated after sputtering the surface titanium oxide film, has been developed to prevent the pumping speed from decreasing by the repeated air exposure and activation process. The result showed the final pressure has not deteriorated even after more than 10 times air exposure and activation. This fact indicated that the surface oxide on the NEG coating would diffuse into the titanium bulk because there is no oxide barrier between the NEG coating and the titanium vacuum chamber.
Herein, an electrochemical oxygen evolution reaction (OER) at the solid–liquid interface was investigated in real time using fluorescence-yield X-ray absorption spectroscopy (XAS) in the soft X-ray region, which is a newly developed technique. A dedicated electrochemical cell was used, and the OER on the surface of a Co/Pt thin film working electrode in an alkaline solution (NaOH, 0.1 M) was investigated. When the electrode potential was shifted to a positive value, the peak of the oxygen K-edge was successfully detected using this technique, and the peak intensity increased in correlation with the electrode potential. In addition, it was indicated that the oxygen K-edge absorption peak was observed, before the electrode potential reaching the onset potential, i.e., from around 1.0 V vs. relative hydrogen electrode of the electrode potential. It was confirmed that the electrochemical reactions at the solid–liquid interface of metal electrodes like the OER catalyst are able to be observed in real-time.
X-ray magnetic linear dichroism (XMLD) is a widely used technique to probe magnetic anisotropy. By measuring absorption while changing the relative angle between crystalline axes and the linear polarization of soft X-rays, one can obtain information about spin orientation of magnets. Due to limitation in the polarization control of soft X-rays, XMLD measurements have conventionally been conducted by rotating samples about a certain axis. Here, we report a new method for XMLD measurements that is realized by continuously rotating the linear-polarization angle using a segmented cross undulator. Through interference of right- and left-handed circularly polarized light, linear polarization is generated at an arbitrary angle. We present a successful demonstration of this XMLD measurement method applied to the antiferromagnet NiO. The new technique will be particularly useful for operando measurements of non-uniform samples where sample size and rotational motion are severely restricted.