Giuseppe Pezzotti

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.

Wear of polyethylene acetabular cups in patients of total hip arthroplasty is routinely deduced from the penetration of the femoral head into the acetabular liner as observed in the radiographs. However, the linear penetration thus measured represents the cumulative contribution of two components, one due to wear, and the other due to creep or irreversible deformation of the polyethylene structure. The erroneous attribution to wear of the entire penetration displacement of the head in the cup might lead to misinterpretation of the actual performance of acetabular cups. The aim of this study was to quantify the head displacement components due to wear and to creep, as they occur in vivo in acetabular cups, and to relate them to the oxidation state of the material by means of advanced Raman spectroscopy procedures. Throughout the investigation, we compared the behaviors on the molecular scale of acetabular cups subjected to different sterilization methods (i.e., γ-irradiation and ethylene oxide treatment).

The cathodoluminescence spectrum of n-GaN crystal has been studied with emphasis placed on its self-absorption behavior. An improved analysis of cathodoluminescence spectral shift with electron penetration depth is shown, according to the following approach: (i) a main band and a sub-band, both of Gaussian nature, are used for spectral convolution; (ii) the observed absorption edge is still described in terms of the Urbach rule, but the Urbach tail is experimentally retrieved by directly using the absorption spectrum (at low energies) obtained from standard cathodoluminescence spectra; (iii) an experimental approach is used to retrieve the actual morphology of the cathodoluminescence probe.

A quantitative assessment of the Raman spectrum emitted from a coarse‐grained polycrystal of multiferroic BiFeO₃ has been carried out by means of a polarized Raman microprobe. The dependence of the intensity of Raman phonon modes has been first theoretically modeled as a function of crystal rotation. Then, the Raman tensor elements have been experimentally determined from the analysis of the A_g and E_g vibrational modes. Copyright © 2009 John Wiley & Sons, Ltd.