Patterned Si thin film electrodes for enhancing structural stability

A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode

Strong Bathochromic Shift of Conjugated Polymer Nanowires Assembled with a Liquid Crystalline Alkyl Benzoic Acid via a Film Dispersion Process

We present aqueous dispersions of conjugated polymer nanowires (CPNWs) with improved light absorption properties aimed at aqueous-based applications. We assembled films of a donor???acceptor-type conjugated polymer and liquid crystalline 4-n-octylbenzoic acid by removing a cosolvent of their mixture solutions, followed by annealing of the films, and then formed aqueous-dispersed CPNWs with an aspect ratio >1000 by dispersing the films under ultrasonication at a basic pH. X-ray and spectroscopy studies showed that the polymer and liquid crystal molecules form independent domains in film assemblies and highly organized layer structures in CPNWs. Our ordered molecular assemblies in films and aqueous dispersions of CPNWs open up a new route to fabricate nanowires of low-band-gap linear conjugated polymers with the absorption maximum at 794 nm remarkably red-shifted from 666 nm of CPNWs prepared by an emulsion process. Our results suggest the presence of semicrystalline polymorphs ??1 and ??2 phases in CPNWs due to long-range ??????? stacking of conjugated backbones in compactly organized lamellar structures. The resulting delocalization with a reduced energy bang gap should be beneficial for enhancing charge transfer and energy-conversion efficiencies in aqueous-based applications such as photocatalysis

Study of metal-insulator transition of the quasi-two-dimensional hole system in the delta-doped GaAs structures

Supervisor:奈 癸聶・材料科学研究科博

Unraveling the Mechanism and Practical Implications of the Sol-Gel Synthesis of Spinel LiMn₂O₄ as a Cathode Material for Li-Ion Batteries: Critical Effects of Cation Distribution at the Matrix Level

Spinel LiMn2O4 (LMO) is a state-of-the-art cathode material for Li-ion batteries. However, the operating voltage and battery life of spinel LMO needs to be improved for application in various modern technologies. Modifying the composition of the spinel LMO material alters its electronic structure, thereby increasing its operating voltage. Additionally, modifying the microstructure of the spinel LMO by controlling the size and distribution of the particles can improve its electrochemical properties. In this study, we elucidate the sol-gel synthesis mechanisms of two common types of sol-gels (modified and unmodified metal complexes)—chelate gel and organic polymeric gel—and investigate their structural and morphological properties and electrochemical performances. This study highlights that uniform distribution of cations during sol-gel formation is important for the growth of LMO crystals. Furthermore, a homogeneous multicomponent sol-gel, necessary to ensure that no conflicting morphologies and structures would degrade the electrochemical performances, can be obtained when the sol-gel has a polymer-like structure and uniformly bound ions; this can be achieved by using additional multifunctional reagents, namely cross-linkers

Structural and Electrochemical Properties of Lithium Nickel Oxide Thin Films

LiNiO2 thin films were fabricated by RF magnetron sputtering. The microstructure of the films was determined by X-ray diffraction and field-emission scanning electron microscopy. The electrochemical properties were investigated with a battery cycler using coin-type half-cells. The LiNiO2 thin films annealed below 500°C had the surface carbonate. The results suggest that surface carbonate interrupted the Li intercalation and deintercalation during charge/discharge. Although the annealing process enhanced the crystallization of LiNiO2, the capacity did not increase. When the annealing temperature was increased to 600°C, the FeCrNiO4 oxide phase was generated and the discharge capacity decreased due to an oxygen deficiency in the LiNiO2 thin film. The ZrO2-coated LiNiO2 thin film provided an improved discharge capacity compared to bare LiNiO2 thin film suggesting that the improved electrochemical characteristic may be attributed to the inhibition of surface carbonate by ZrO2 coating layer

Electrochemical Properties of Multilayered Sn/TiNi Shape-Memory-Alloy Thin-Film Electrodes for High-Performance Anodes in Li-Ion Batteries

Sn is a promising candidate anode material with a high theoretical capacity (994 mAh/g). However, the drastic structural changes of Sn particles caused by their pulverization and aggregation during charge–discharge cycling reduce their capacity over time. To overcome this, a TiNi shape memory alloy (SMA) was introduced as a buffer matrix. Sn/TiNi SMA multilayer thin films were deposited on Cu foil using a DC magnetron sputtering system. When the TiNi alloy was employed at the bottom of a Sn thin film, it did not adequately buffer the volume changes and internal stress of Sn, and stress absorption was not evident. However, an electrode with an additional top layer of room-temperature-deposition TiNi (TiNi(RT)) lost capacity much more slowly than the Sn or Sn/TiNi electrodes, retaining 50% capacity up to 40 cycles. Moreover, the charge-transfer resistance decreased from 318.1 Ω after one cycle to 246.1 Ω after twenty. The improved cycle performance indicates that the TiNi(RT) and TiNi-alloy thin films overall held the Sn thin film. The structure was changed so that Li and Sn reacted well; the stress-absorption effect was observed in the TiNi SMA thin films

Differences in Clinical Manifestations according to the Positivity of Interferon-γ Assay in Patients with Intestinal Tuberculosis

Intestinal tuberculosis (ITB) remains prevalent in Asia. An interferon-γ assay (QuantiFERON-TB gold test [QFT]) is considered to be an effective supplementary tool for diagnosing ITB. We retrospectively analyzed the clinical features of ITB patients based on the initial results of QFT. A total of 109 patients with ITB were enrolled, and 82 patients (75.2%) showed positive QFT results. In the QFT-positive group, the mean age (44.1±12.0 years) was significantly higher than that in the QFT-negative group (37.0±14.8, p=0.0096). Abdominal pain (p=0.006) and diarrhea (p=0.030) were more frequent in the QFT-negative group. Further, C-reactive protein (CRP) levels were significantly higher in the QFT-negative group (6.4±9.9 mg/dL) than in the QFT-positive group (1.3±2.3, p<0.001). Multivariate analysis confirmed that younger age (p=0.016), diarrhea (p=0.042), and high levels of CRP (p=0.029) were independent predictors of QFT-negative results in patients with ITB. These results suggest that prior exposure to TB, reflected by QFT positivity, may cause mild inflammation in patients with ITB