T. Zorba

Hydroxy Carbonate Apatite Formation on Particulate Bioglass In Vitro as a Function of Time

The mechanism of bonding of bioactive glasses with living tissues has been reported to be associated with the development of a layer consisting of carbonate-containing hydroxyapatite similar to that of bone on the surface of the materials. This layer is also formed in vitro, in solutions with ion concentrations similar to those of human blood plasma, like SBF (Simulated Body Fluid). The development of HCAp (Hydroxy carbonate apatite) layer on the surface of a commercially available Bioglass® Synthetic Bone Graft Particulate (Perioglas®) after immersion in SBF solution using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with associated Energy Dispersive Spectroscopy (EDS). PerioGlas® powder with particle size 20-63μm, pressed in a vacuum press in order to produce pellets. The pellets were soaked in SBF for 12, 18, 24 and 48 hours at 37°C. Results revealed the formation of an amorphous CaO-P 2 O 5 - rich layer on the surface of the specimens after 12 hours in the solution and a well crystalline HCAp layer after 24 hours immersion time.

Infrared spectroscopic and electronic transport properties of polycrystalline semiconducting FeSi2 thin films

Polycrystalline semiconducting FeSi2 thin films were grown on (100) Si substrates of high resistivity by electron beam evaporation of amorphous Si/Fe ultrathin multilayers in an ultrahigh vacuum system, followed by conventional vacuum furnace (CF) or rapid thermal annealing (RTA). Infrared reflectance and transmittance measurements were employed for optical characterization of the samples at room temperature. The results indicate a direct transition at about 0.85 eV, an indirect transition at about 0.79 eV, and exponential band tail states within the band gap. The quality of the silicide is improved by increasing the annealing temperature from 600 to 800 °C in the RTA process, while the opposite is observed in the CF annealed samples. Transport measurements were performed on a typical β‐FeSi2 layer of high quality grown by CF at low temperature. The measured mobility is about 97 cm2/V s and the hole concentration is about 1×1017 cm−3. The mobility is a factor of 10 higher and the hole concentration a fact...

Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations.

OBJECTIVES Dental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations. METHODS One hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max(®) ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (nx=60) were divided in three groups (control, aged for 5h, aged for 10h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P<0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ0). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. RESULTS A slight increase of the flexural strength after 5h, and a decrease after 10h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P<0.05). Both ceramics presented a t→m phase transformation, with the m-phase increasing from 4 to 5% at 5h to around 15% after 10h. SIGNIFICANCE The significant reduction of the flexural strength after 10h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested.

Synthesis and characterization of LiMn2O4 for use in Li-ion batteries

Lithiated spinel manganese dioxide was synthesised from electrochemical MnO 2 and Li2CO 3 with deficiency or excess lithium (Li x Mn 2 O 4 , 0.8 <x < 1.3) for use in Li/Li x Mn 2 O 4 and Li-ion cells. Micron-sized Li 1.05 Mn 2 O 4 prepared at 730°C showed high Li utilization, excellent cyclability and good rate capability with an initial discharge capacity of 123 mA h/g and 10% discharge capacity reduction after 20 cycles. Different types of commercial carbonaceous materials were also investigated with respect to their electrochemical performance vs. Li. Unoptimised Li-ion cells, using Li 1.05 Mn 2 O 4 prepared at 730°C as the cathode material, EC-DMC-LiPF 6 electrolyte and carbon fibres, showed promising performance characteristics.

Optical characterization of thin and ultrathin surface and buried cubic SiC layers using FTIR spectroscopy

Abstract We use infrared reflectance spectroscopy from 20 to 5000cm −1 to evaluate the structural, optical and electrical properties of surface cubic β-SiC thin layers, either epitaxially grown by chemical vapor deposition and sputtering on Si substrates, or of buried β-SiC layers synthesized by implantation of high doses of C + ions into Si. The quality control can be finished within minutes after SiC film growth, while the determination of the important physical parameters can be made in less than 1h.

Infrared lattice spectra of Tm3Al5O12 and Yb3Al5O12 single crystals

The reflectance spectra of the Tm3Al5O12 and Yb3Al5O12 single crystals have been studied at room temperature. Fifteen infrared-active modes, out of the 17 theoretically predicted, have been experimentally observed. The infrared data have been analysed by means of the Kramers-Kronig transformation to yield the complex dielectric function, the complex refractive index, the absorption coefficient, as well as the frequencies of the longitudinal (ωLO) and transverse (ωTO) long-wavelength T1u modes. Furthermore, the experimental data are compared and discussed in the light of theoretical lattice dynamical calculations based on the rigid-ion model.

Optical and electrical characterization of high quality β-FeSi2 thin films grown by solid phase epitaxy

Abstract High quality β-FeSi 2 thin films were grown on Si〈100〉 substrates by UHV electron beam evaporation of α-Si/Fe multilayers and annealed by conventional vacuum furnace and rapid thermal techniques. Infrared spectroscopy (reflectance and transmittance) and electrical measurements were employed to characterize the films. Hall measurements performed on the thin films yielded exceptionally high free carrier mobilities, up to 112 cm 2 /Vs.

Electron cyclotron resonance deposition, structure, and properties of oxygen incorporated hydrogenated diamondlike amorphous carbon films

Oxygen-incorporated hydrogenated amorphous carbon films were grown by the integrated distributed electron cyclotron resonance plasma technique from a mixture of acetylene and oxygen. It has been found that the increase of the oxygen to acetylene gas ratio results in more oxygen incorporation up to O∕(O+C)=0.2 with a decrease in the hydrogen concentration within the film as measured by the nuclear reaction analysis (NRA) and a combination of the elastic recoil detection analysis and Rutherford backscattering techniques. The spectroscopic ellipsometry in the range of 1.5–5eV showed a negligible decrease of the E04 optical band gap for increasing the oxygen content. At the same time, the decrease of the refractive index from 2.2 to 2.0 denotes the decrease of the films density, which was independently estimated by NRA. The visible (488nm) Raman spectroscopy showed that the increase of the oxygen content favors the clustering of the six-fold sp2C rings. The Fourier transform infrared spectroscopy gives eviden...

An infrared study of Ge+ implanted SiC

Abstract The damage produced by 200 keV Ge + ion implantation in 6H-SiC (from Cree Research) has been studied by fast Fourier transform infrared (IR) reflectance spectroscopy. A new, recently developed at the spectroscopy laboratory of AUTh, non-destructive optical method, based on the normalized atomic vibrational damping of the ‘reststrahlen band’, has been applied to determine damage depth profiles of SiC for damage over three orders of magnitude, up to amorphisation. For the amorphized state IR results show an up to 30% reduction of heteronuclear SiC bonds. No new broad SiSi or CC vibrational bands were observed.

Structural and Compositional Characterization of High Energy Separation by Implantation of Oxygen Structures Using Infrared Spectroscopy

Silicon was implanted with 2 MeV O + ions with doses covering the range from 1 x 10 17 to 2 x 10 18 O + cm -2 , at an implantation temperature of 700°C. Subsequently, samples were capped and annealed at 1300°C. Infrared reflectance spectroscopy has been used in order to characterize the as-implanted and annealed samples. The optical modeling of the multilayer structures and the data reduction procedure are given in detail. The thickness, chemical composition, crystallinity, interface macroscopic roughness, and refractive index profiles are quantified. It is shown that infrared reflectance spectroscopy is a quick, nondestructive, analytical, and precise method for characterizing high energy separation by implantation of oxygen (SIMOX) structures. Cross correlation with H + beam Rutherford backscattering/channeling, secondary ion mass spectroscopy, and cross-sectional transmission electron microscopy results, gives good agreement. The formation of oxide in the high energy region follows the same basic rules as in the standard SIMOX case. No anomalous oxygen diffusion was observed during annealing and a buried layer formed during annealing even for the lowest dose. It is found that the microstructure of the annealed samples is strongly dependent on the implantation conditions such as beam current density and that even for the highest dose of 2 x 10 18 O + cm -2 , a continuous stoichiometric silicon dioxide layer has not formed after annealing.