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Zhu W.,Kyoto Institute of Technology | Zhu W.,Osaka University | Leto A.,Piezotech Japan Ltd. | Hashimoto K.-Y.,Chiba University | Pezzotti G.,Kyoto Institute of Technology
Thin Solid Films | Year: 2013

Raman spectroscopy and scanning electron microscopy, combined with the Vickers indentation method, were applied to analyze the fracture behavior of a thin (i.e., 1 μm in thickness) aluminum nitride (AlN) film deposited on a (001)Si substrate. A series of indentations were introduced in the AlN/Si system with applying gradually increasing loads, and the stress intensity factor, KR, stored at the tip of cracks propagated from the indentation corners was determined according to the shift of selected Raman bands from wurtzitic AlN in response to the crack-tip residual stress field. A steeply rising crack resistance curve was found in the AlN film, starting from an intrinsic toughness, KI0 = 0.6 MPa m1/2, for crack initiation up to KR ≅ 5 MPa m1/2 (at a crack length of ~ 120 μm). Such rising R-curve behavior was attributed to the presence of a compressive residual stress field stored in the AlN film. The results obtained by Raman spectroscopy were consistently supported by direct crack opening displacement measurements in a scanning electron microscope. © 2013 Elsevier B.V.

Zhu W.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Hashimoto K.-Y.,Chiba University | Pezzotti G.,Kyoto Institute of Technology
Journal of Applied Physics | Year: 2012

A controlled biaxial stress field generated in a ball-on-ring configuration was applied on a thin hexagonal (0001)AlN film grown on (001)Si substrate, and the phonon deformation potential (PDP) constants of the A1 (TO), E2 (high), and A1 (LO) Raman modes were retrieved from the respective spectral shifts. Measurements were done: (i) at given fixed locations upon increasing the externally applied load; and (ii) along spectral line scans performed at a fixed load. The reliability of the retrieved PDP values, in comparison with values previously reported in the literature, was examined by a further evaluation of the residual stress field stored in the AlN/Si system associated with the tip of a crack propagated from the corner of a pyramidal indentation. The PDP assessments were confirmed to be reliable owing to a close correspondence among stress intensity factors independently retrieved from different Raman bands. © 2012 American Institute of Physics.

Battiston S.,CNR Institute for Energetics and Interphases | Battiston S.,University of Padua | Minella M.,University of Turin | Gerbasi R.,CNR Institute of Inorganic and Surface Chemistry | And 7 more authors.
Carbon | Year: 2010

A novel titanium dioxide architecture, called titanium dioxide nanopetals, was obtained through two sequential vapour techniques, metal-organic chemical vapour deposition (MOCVD) and magnetron sputtering on a single wall carbon nanohorn (SWCNH) bed, resulting in a surprising synergistic effect. The new composite material was characterized by scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The particular experimental conditions under which this unusual growth was obtained are discussed in detail. The photocatalytic degradation of phenol under UV light irradiation demonstrated that this novel material exhibited a significant increase of photoactivity in comparison with the titanium dioxide thin films deposited by RF magnetron sputtering and the SWCNHs coated with titanium dioxide by MOCVD. © 2010 Elsevier Ltd. All rights reserved.

Boffelli M.,University of Venice | Boffelli M.,Kyoto Institute of Technology | Back M.,University of Venice | Cattaruzza E.,University of Venice | And 5 more authors.
Journal of Physical Chemistry C | Year: 2013

Cathodoluminescence spectroscopy and X-ray photoelectron spectroscopy were concurrently used to investigate the local physicochemical nature of the amorphous lattice in pure SiO2 and N-doped SiO2 thin films prepared by radiofrequency magnetron sputtering (the latter samples deposited under a set of different conditions of N2 partial pressure). The main aim of this investigation was twofold: (i) to extend our knowledge of the physical and chemical structure of SiO2 films and (ii) to explore our capacity of manipulating, fine tuning, and measuring their stoichiometry characteristics. The presence of nitrogen atoms in the amorphous host structure was confirmed to significantly affect the formation of oxygen-deficient centers, nonbridging oxygen hole centers, and other kinds of defect complexes. The main challenge here was to relate the variations in type and concentration of these peculiar defects to the processing conditions and to the amount of nitrogen incorporated in the SiO2 amorphous matrix. The evolution of both pure and doped systems was monitored with increasing the temperature of an annealing cycle following film deposition (1 h in air, at temperatures ranging between 50 and 1200 C, with 50 C step). Stoichiometry changes could thus be clarified and temperature thresholds found for the annihilation of N sites and for the formation of a pseudoequilibrium stoichiometric structure in silica glass. © 2013 American Chemical Society.

Puppulin L.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Hasegawa M.,Mie University | Pezzotti G.,Kyoto Institute of Technology
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

The impact of adding antioxidant vitamin-E (α-tocopherol) to the microstructure of ultrahigh molecular weight polyethylene (UHMWPE) for total knee arthroplasty has been studied in detail by means of Raman microprobe spectroscopy. Three tibial insert samples prepared by different manufacturing methods were investigated, as follows: (A) a sample manufactured without blending with vitamin E which did not receive any irradiation dose after consolidation but underwent final sterilization in ethylene oxide (EtO); (B) a sample blended with 0.3. wt% of α-tocopherol, an isomer of vitamin E, and manufactured as sample (A); and, (C) a sample in which vitamin E was diffused after being irradiated with 100. kGy dose of γ-ray. Clear microstructural differences were observed in terms of phase contents (i.e., amorphous, crystalline, and intermediate phase fraction), molecular orientation, and the degree of anisotropy between the investigated tibial plates. Vitamin E in the starting resin promoted chain mobility leading to reorganization of the molecular chains. The spectroscopic characterizations helps to rationalize the complex effect of vitamin-E on the UHMWPE microstructure and gives useful information on how significantly any single step of the manufacturing procedures might affect the mechanical properties of the final orthopedic component. © 2014 Elsevier Ltd.

Fukatsu K.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Zhu W.,Osaka University | Sugano N.,Osaka University | And 2 more authors.
Acta Biomaterialia | Year: 2012

The low-temperature polymorphic transformation behavior of two types of commercially available femoral head, both made of 3 mol.% Y 2O 3-stabilized tetragonal ZrO 2 polycrystals (3Y-TZP), was examined by in vitro experiments. Both materials contained a small amount (0.25 wt.%) of Al 2O 3, but they differed slightly in their SiO 2 impurity content, in the morphology and crystallinity of the dispersed Al 2O 3 phase, and in grain size. In vitro experiments were conducted in a water-vapor environment at temperatures in the range 90-134 °C and for periods of time up to 500 h. Despite the materials having the same nominal composition, quite different behaviors were found in the hydrothermal environment for the two types of femoral head investigated. A phenomenological description of the kinetics of monoclinic nuclei formation/growth led to the experimental determination of activation energy values for the environmentally driven polymorphic transformation. From the material physics viewpoint, cathodoluminescence spectroscopy enabled us to rationalize the role of surface stoichiometry on the mechanisms leading to polymorphic transformation. Spectroscopic experiments unveiled some new relevant aspects of surface off-stoichiometry, which lie behind the different phase transformation kinetics experienced by the investigated femoral heads. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Leto A.,Piezotech Japan Ltd. | Zhu W.,Osaka University | Matsubara M.,Nissan Tamagawa Hospital | Pezzotti G.,Kyoto Institute of Technology
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

Raman and cathodoluminescence spectroscopic methods were employed for clarifying important stoichiometric and mechanical properties so far missing in the specification of the physical origin of the structural behavior of Oxinium™ femoral head components. Spectroscopy proved helpful in rationalizing the actual physical and chemical reasons behind the mechanical integrity of the ceramic-film/metal-substrate interface, which is responsible for both the good adherence and the surface durability reported in prosthetic applications of Oxinium™ components. Raman spectroscopy coupled with the crack opening displacement (COD) method was used to evaluate the intrinsic fracture toughness of the surface oxide film. In addition, cathodoluminescence spectroscopy provided new evidences on both the oxygen vacancy gradient developed during the metal-oxidation manufacturing process and the bioinertness of Oxinium™ femoral components. © 2013 Elsevier Ltd.

Puppulin L.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Wenliang Z.,Osaka University | Sugano N.,Osaka University | And 2 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

The literature on tribological assessments of artificial hip joints usually focuses on correlations between joint composition, size, and specific wear rates, but conspicuously ignores the physical aspects behind the occurrence of degradation mechanisms of friction and wear. Surface degradation in artificial joints occurs because of increases in temperature and local exacerbation of contact stresses inside the moving contact as a consequence of physical and chemical modifications of the sliding surfaces. This article reports about the development of a new pin-on-ball spectroscopy-assisted tribometer device that enables investigating also physical rather than merely engineering aspects of wear processes using in situ Raman and fluorescence techniques. This innovative tribometer is designed to bring about, in addition to conventional tribological parameters, also information of temperature, stress and phase transformations in the femoral heads as received from the manufacturer. Raman and fluorescence spectra at the point of sliding contact are recorded durilng reciprocating hard-on-hard dry-sliding tests. Preliminary results were collected on two different commercially available ceramic-on-ceramic hip joint bearing couples, made of monolithic alumina and alumina-zirconia composites. Although the composite couple showed direct evidence of tetragonal-to-monoclinic phase transformation, which enhanced the coefficient of friction, the specific wear rate was significantly lower than that of the monolithic one (i.e., by a factor 2.63 and 4.48 on the pin and head side, respectively). In situ collected data compared to ex situ analyses elucidated the surface degradation processes and clarified the origin for the higher wear resistance of the composite as compared to the monolithic couple. © 2013 Elsevier Ltd.

Zhu W.,Osaka University | Puppulin L.,Kyoto Institute of Technology | Leto A.,Piezotech Japan Ltd. | Takahashi Y.,Kyoto Institute of Technology | And 3 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

Fluorescence microprobe spectroscopy was applied to in situ assessments of contact stress and local temperature at the contact point of dry-sliding couples during wear tests of two commercially available ceramic-on-ceramic femoral heads. The investigated ceramic hip implants consisted of either monolithic Al2O3 or Al2O3/ZrO2 composite. A specially designed pin-on-ball tribometer was employed, which enabled directly testing the femoral head components as received from the maker without further manipulation. The strong fluorescence emission from Cr3+ impurities contained in Al2O3 served as a responsive sensor for both temperature and stress. Analytical corrections for the averaging effects arising from the finite size of the laser probe were made according to a probe response formalism in which geometrical conditions of the sliding couple were incorporated as boundary conditions. The sample-probe interaction at the contact point was then experimentally calibrated by obtaining probe response functions for the two materials investigated. Based on such theoretical and experimental procedures, deconvolutive computational routines could be set up and the true variations of local temperature and stress at the contact point of the bearing surfaces retrieved from the observed time-dependent broadening and shift of a selected spectral band, respectively. The main result of the in situ investigation was that the monolithic sliding couple showed both significantly lower temperature and lower magnitude of compressive stress at the contact point as compared to the composite one, although the composite couple wore at a significantly lower specific wear rate than the monolithic one. © 2013 Elsevier Ltd.

Leto A.,Piezotech Japan Ltd. | Pezzotti G.,Kyoto Institute of Technology
Physica Status Solidi (A) Applications and Materials Science | Year: 2011

The mechanical properties and the functional behavior of inorganic dielectric materials strongly depend on the stoichiometry imbalance in the material and its structural accommodation. Point defect populations are responsible for departures from the normal stoichiometric formula and clear correlations have been documented between the magnitude of the dielectric constant of a compound and the structural mode by which it accommodates its non-stoichiometry. In this study, we systematically apply the cathodoluminescence (CL) method to local stoichiometry characterizations of advanced silica and barium titanate compounds as paradigm inorganic dielectric materials with amorphous and nanocrystalline structure, respectively. The CL spectral emission is shown here capable not only to clarify the off-stoichiometric characteristics of dielectric devices, but also to provide a useful probe for assessing the local stress state at the interfaces between the dielectric and the conductor materials. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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