Layerwise antiferromagnetically-coupled bct-Mn(001) ultra-thin monolayer films grown on bcc-Fe(001) at 370 K have been studied as an ideal interface between ferromagnet and antiferromagnet with the Néel temperature much higher than room temperature, which is the key issue to understand exchange bias in magneto resistance junctions. Also, the Mn(001) films on Fe(001) have been used as one of standard samples to examine spin-polarized scanning tunneling microscopy (SP-STM) measurements. Here, we demonstrated how the interface roughness between ferromagnet and antiferromagnet changes magnetic structures of the films. SP-STM magnetic imaging was performed on Mn(001) films grown on an Fe(001)-whisker at 470 K in ultrahigh vacuum. Although magnetic images showed the layerwise antiferromagnetic coupling between layers, additional magnetic structures were found, namely 3-nm-size 180° magnetic domains due to interface intermixing and non-collinear magnetic coupling areas due to a dense interface step density.
Monolayer deposition of cobalt was demonstrated on a well-ordered ring molecular array at room temperature in ultra-high vacuum by means of home-built low-temperature scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy (UPS) setups. Sub-monolayer cobalt (Co) was deposited on a (7×4) array of 4,4′,5,5′-tetrabromodibenzo crown-6 ether (Br-CR) molecules grown on Cu(111). The adsorbed Co atoms were found to intercalate and deconstruct the well-ordered molecular structure, providing Co and Br-CR mixing clusters.
To experimentally obtain the mass absorption coefficient (μ) of low-Z elements in soft X-ray regions using solid materials, soft X-ray absorption spectra in a 200～800 eV region of polyethyleneterephtalate (PET) film with a thickness of 700 nm were measured with the transmission and total electron yield (TEY) methods. Soft X-ray absorption measurements were performed in a beamline BL-6.3.2 at the Advanced Light Source (ALS). In O K region, XANES profile with absorbance was in good agreement with that with TEY, which suggests the sufficient transmission of X-rays in the PET film at the O K region. The measured μ spectrum in scattering region was also in good agreement with the calculated spectrum. The μ spectrum in photoelectric absorption region was successfully measured. Typical μ value of O in PET films can be determined as 2.2×104 cm2 g－1 at 542 eV (σ*).
Photocatalytic steam-methane reforming is an attractive chemical technology for hydrogen production from abundant resources of methane and water. In the case of photocatalytic reaction, photo-generated electron plays key roles in hydrogen production. However, the dynamics of photogenerated electrons under reaction condition have been unclear. To uncover the behavior of reactive photo-excited electrons, we conducted operando FT-IR spectroscopy of metal loaded Ga2O3 photocatalysts under irradiation of intensity modulated UV light. We succeeded in observing a correlation between the reaction activity and a broad mid-infrared absorption band derived from the photo-generated electrons shallowly trapped at the photocatalyst surfaces.
In this study, short-wave near-infrared (SWNIR) band pass filters (BPF) using hydrogenated amorphous silicon (a-Si:H) were fabricated by reactive sputtering method at 200℃, and their optical performance and thermal durability were evaluated. The sample of the lowest extinction coefficient (k＜1×10－3) and the highest durability was obtained at H2 partial pressure ratio of 30% for a-Si:H. The transmittance of the BPF with stacked a-Si:H (H2＝30%) and SiO2 was more than 90%. Its optical characteristics were consistent well with the simulation. It was found that the characteristics of BPF correlated with the optical properties of a-Si:H stemmed from structural relaxation and hydrogen composition. It was also suggested that the stable performance of the BPF could be expected below 250℃.
We demonstrated that vertically aligned single-walled carbon nanotubes (VA-SWCNTs) can be grown by alcohol catalytic chemical vapor deposition (CVD) using an Ir catalyst in a cold-wall CVD system. VA-SWCNTs were directly grown on SiO2/Si substrates with neither any buffer layers nor cocatalysts under an ethanol pressure of 1×10－1 Pa at 800℃. The SWCNT length became longer with increasing growth time and the VA-SWCNT thickness reached ∼4 µm after the growth for 180 min. The diameters of the grown SWCNTs were mainly distributed between 0.8 and 1.2 nm, which is much smaller than those from Fe and Co catalysts. X-ray absorption fine structure spectroscopy result showed that the Ir catalyst retained metallic phase during SWCNT growth, which is in marked contrast with SWCNT growth from Fe and Co catalysts.
In this review, we summarize recent progress achieved in on-surface bottom-up growth of graphene nanoribbons (GNRs) with well-defined edges. First, we show the simulation results suggesting that a GNR backward diode with GNR heterojunction can outperform the state-of-the-art diodes owing to their negligible junction capacitance. The major challenge required for achieving high-performance GNR diodes is low contact resistance and well-defined GNR heterojunction. The second part of this review is dedicated to our recent works on GNR heterojunctions by modifying electronic states by edge-functionalization. It was revealed that the important design policies for precursors are as follows : molecular design avoiding intramolecular steric hinderance upon polymerization, precursor design considering dehydrogenation path, and precursor design considering intramolecular side reaction. We also demonstrate our preliminary results of GNR-FET, which suggest that wider GNRs with narrower band gap is required for the electronic devices.