資料公開

資料公開

タイトル Effect of component content variation on composition and structure of activated carbon in PVDF:K2CO3 for supercapacitors
カテゴリ 研究論文
概要 Percolative composites consisting of potassium carbonate dispersed in polyvinylidene fluoride (PVDF) polymeric matrix have shown high dielectric constant and electrical conductivity due to the formation of chemically activated carbon interfaces in the composite. In this paper, a series of PVDF/K2CO3 films with different component contents were prepared and investigated by Raman and X-ray photoelectron spectroscopies to clarify chemical composition, structure and formation mechanism of activated carbon. The results revealed the presence of a reaction loop to consume both constituent phases, and the formation of sp2 carbon rings in the yielded activated carbon due to cross-linking dehydrofluorination of PVDF during thermal treatment. The sp2 content showed a non-linear dependence on K2CO3 content with the presence of an optimal value corresponding to the best performance. This study thus can give a direction in future fabrication of PVDF/K2CO3 electrode materials for supercapacitors
タイトル Raman spectroscopic studies of stress-induced structure alteration in diamond-like carbon films.
カテゴリ 研究論文
概要 In this paper, Raman spectral mappings were carried out on Vickers indentation prints introduced on DLC films prepared with different substrate bias voltages (SBV). The mapping results showed clear differences in the intensity ratio, ID/IG, and band shifts for D and G peaks in samples fabricated with and without applying SBV. These spectral characteristics arose from the cumulative effect of a compressive (residual) stress field and structural alterations including sp2 and sp3 carbon disorder upon generation of the indentation print. Additional quantitative stress analyses, which employed spectral line scans on the film cross sections, revealed clear differences in magnitude for the compressive stresses stored in the films, as well as in-depth structural variations resulting from different SBV being applied during fabrication. An increasing level of residual compressive stress in the DLC films with increasing SBV may directly contribute to the observed decreased adhesion to the substrates and to the increased Vickers hardness.
タイトル Structural alteration induced by substrate bias voltage variation in diamond-like carbon films fabricated by unbalanced magnetron sputtering
カテゴリ 研究論文
概要 Diamond-like carbon films/coatings (DLC) can be employed in a wide range of applications, but the film quality and performance are strongly dependent on the deposition conditions. In this paper, we attempted to clarify the structural and compositional alterations induced by substrate bias voltage (SBV) variation in DLC films by employing different spectroscopic analyses and to correlate them with the variations of two important film properties, hardness and adhesion energy. A series of DLC films fabricated by unbalanced magnetron sputtering with changing substrate bias voltage were investigated by Raman, FTIR and X-ray photoelectron spectroscopies. The results revealed the presence of sp2 and sp3 carbon chains and rings and various types of hydrocarbon in the tetrahedral amorphous carbon films due to incorporation of hydrogen and oxygen. The reduction in hydrogen content together with a generation of sp2 hydrocarbon rings in response to SBV increase were responsible for increases in Young’s modulus and hardness, and, concurrently, for a decrease in film adhesion energy.
タイトル Mechanisms induced by transition metal contaminants and their effect on the hydrothermal stability of zirconia-containing bioceramics: An XPS study
カテゴリ 研究論文
概要 Zirconia containing bioceramics suffer low temperature degradation in biological and hydrothermal environments, and the presence of transition metal contamination has been shown to greatly affect zirconia stability in different materials. In this paper, X-ray photoelectron spectroscopy was applied to investigate the compositional and structural variations of different zirconia containing hip-joint bioceramics with and without transition metal stains in hydrothermal environments. Non-stained and stainless-steel-stained femoral head samples of 3 mol% Y2O3 doped tetragonal zirconia polycrystals (3Y-TZP) and zirconia-toughened alumina (ZTA) subjected to isothermal treatments in water vapor were investigated with quantifying their respective compositional XP lines. The outputs of these spectroscopic experiments revealed a significant difference in the off-stoichiometric reactions taking place at the surface of zirconia-containing ceramics in presence and absence of transition metal contamination. The complex off-stoichiometric chemistry that occurred in the presence of metal contaminants could be interpreted in terms of defect-related chemical reactions among metal, water vapor, and oxide lattice, with a crucial contribution of the alumina phase in the transformation kinetics of ZTA.
タイトル Structure and composition evaluation of heavily Ge-doped ZnO nanocrystal films
カテゴリ 研究論文
概要 A series of high quality ZnO nanocrystal films doped with Ge at different Ge/Zn molar ratios were synthesized by the sol-gel method, and the structural and compositional changes induced by Ge doping in the ZnO films were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and cathodoluminescence spectroscopy. Heavy Ge doping in ZnO was found to effectively reduce the intrinsic defects in the films and suppress the free exciton emission and the defect-related emissions in the visible green-red region, by the substitution of Ge at Zn sites and the formation of non-radiative deep-level traps (GeZn)+. The generation of such non-radiative traps was found to be suppressed with respect to the dopant increase, because of a reduction in carrier concentration along with a formation of stable defect complex GeZn–VZn at high doping content. The clarification of defect alterations in Ge-doped ZnO lays the foundation of quantitative evaluation of defect effects on the electrical and optical properties for improving the quality of GeZnO devices.
タイトル Transition metals increase hydrothermal stability of yttria-tetragonal zirconia polycrystals (3Y-TZP)
カテゴリ 研究論文
概要 In this paper, the influence of transition metals on phase stability of zirconia in 3 mol% Y2O3 doped tetragonal zirconia polycrystals (3Y-TZP) in hydrothermal environments was reported. 3Y-TZP with and without stainless-steel or CoCr metal stains on the sample surface were subjected to different isothermal treatments in water vapor, and their respective monoclinic fractions were quantified by confocal Raman spectroscopy. The outputs of these spectroscopic experiments revealed transition metals conspicuously could stabilize the tetragonal zirconia polymorph in the monolithic zirconia, possibly due to the occurrence of off-stoichiometric chemistry in the presence of metal stains.
タイトル Reconciling in vivo and in vitro kinetics of the polymorphic transformation in zirconia-toughened alumina for hip joints: III. Molecular scale mechanisms
カテゴリ 研究論文
概要 Understanding the intrinsic reason(s) for the enhanced tetragonal to monoclinic (t → m) polymorphic phase transformation observed on metal-stained surfaces of zirco-nia-toughened alumina (ZTA) requires detailed knowledge of off-stoichiometry reac-tions at the molecular scale. In turn, information regarding the mechanism(s) for ox-ygen vacancy creation or annihilation at the material surface is a necessary prerequisite. As a crucial aspect of the surface destabilization phenomenon, the availability of electrons and holes which allow for vacancy creation/annihilation is considered in this paper. Metal-enhanced alterations of the oxygen sublattice in both Al2O3 and ZrO2 of the ZTA composite play a decisive role in the polymorphic transformation. According to spectroscopic evidence obtained through nanometer-scale analyses, enhanced annihilation of oxygen vacancies in Al2O3 and ZrO2 occurs near the metal stain, while the overall Al2O3 lattice tends to dehydroxylate by forming oxygen vacancies. A mechanism for this chemically driven “reactive metastability” is suggested which re-sults in accelerating the polymorphic transformation. The Al2O3 matrix is found to play a key-role in the ZrO2 transformation process, with unambiguous confirmation of oxygen and hydrogen transport at the material surface. It is postulated that this transport is mediated by migration of dissociated elements at the metal surface be-cause they are readily and abundantly made available by the surrounding thermally activated hydrothermal environment.
タイトル Chemistry-driven structural alterations in short-term retrieved ceramic-on-metal hip implants: evidence for in vivo incompatibility between ceramic and metal counterparts.
カテゴリ 研究論文
概要 Ceramic-on-metal (CoM) hip implants were reported to experience lower wear rates in vitro as compared to metal-on-metal (MoM) bearings, thus hinting metal-ion release at lower levels in vivo. In this paper, we show a spectroscopic study of two short-term retrieval cases of zirconia-toughened alumina (ZTA) femoral heads belonging to CoM hip prostheses, which instead showed poor wear performances in vivo. Metal contamination and abnormally high fractions of tetragonal-to-monoclinic (tm) polymorphic transformation of the zirconia phase could be found on both ZTA heads, which contrasted with the optimistic predictions of in vitro experiments. At the molecular scale, incorporation of metal ions into the ceramic lattices could be recognized as due to frictionally assisted phenomena occurring at the ceramic surface. Driven by abnormal friction, diffusion of metal ions induced lattice shrinkage in the zirconia phases, while residual stress fields became stored at the surface of the femoral head. Diffusional alterations destabilized the chemistry of the ceramic surface and resulted in an abnormal increase in tm phase transformation in vivo. Frictionally driven metal transfer to the ceramic lattice thus hinders the in vivo performance of CoM prostheses.
タイトル Analysis of defect luminescence in Ga-doped ZnO nanoparticles
カテゴリ 研究論文
概要 We applied cathodoluminescence (CL) spectroscopy to evaluate the defect-induced luminescence within ZnO and Ga-doped ZnO (GZO) nanoparticles. The observed emissions from defect sites present in the GZO lattice exhibited a strong dependence on both dopant content and synthesis methods. The strong and broad defect-induced emissions and inhomogeneous population of intrinsic defects in nano-sized ZnO particles could effectively be suppressed by Ga doping, although large dopant amounts caused the generation of negatively-charged defects, VZn and Oi, with a subsequent increase of the luminescence. Upon deconvolution of the retrieved CL spectra into individual sub-bands, the physical origin of all the sub-bands could be clarified, and related to sample composition and synthesis protocol. This study lays the foundation of quantitative CL evaluation of defects to assess the quality of GZO optoelectronic devices.
タイトル Point-defect populations as induced by cation/anion substitution in β‑Si3N4 lattice. A cathodoluminescence study
カテゴリ 研究論文
概要 Point-defect characterizations in bulk β-silicon nitride polycrystalline ceramics were performed by means of cathodoluminescence (CL) spectroscopy. Three kinds of samples were compared: undoped Si3N4, SiO2-doped Si3N4, and Si3N4 doped with Al2O3 and Y2O3. Intrinsic defects and the effect of anion and cation substitutions (i.e., O for N and Al(Y) for Si) on the spectroscopic behavior of defect emissions were investigated with the aim of assigning the physical origin of the observed CL spectra. Upon deconvoluting the retrieved CL spectra into individual sub-bands, emissions originating from different defects stored in the neighborhood of the surface of these materials could be classified. A clear dependence of defect type and content on the presence of dopants could be found, despite the well-known notion that most of the dopant ions reside at grain boundaries rather than being assimilated into the hexagonal structure of β-silicon nitride.