Papers by Author: Alessandro Alan Porporati

Abstract: A spatially resolved cathodoluminescence (CL) analysis is used as a means for chemical and mechanical analyses of the composite surface after environmental exposure. CL emission proves extremely efficient in concurrently monitoring the concentration of point defects (e.g., oxygen vacancies) on the material surface. Using CL, averaging effects from sub-surface parts of the material can be minimized, and the actual chemical state of the material surface is revealed. As a result, information about the stoichiometry of the material surface can be obtained directly from the lattices of the constituent phases, this enabling one to pattern relevant connections to the environmental resistance of oxide-based bioceramics. A highly fracture resistant alumina/zirconia composite represents the latest trend in ceramics for arthroplastic applications in alternative to monolithic alumina or zirconia ceramics. This composite material is designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo, an important step forward in the full exploitation of ceramic materials in the field of arthroplasty. Systematically monitoring the optical activity of oxygen vacancies in both alumina and zirconia phase reveals the distinct role on the kinetics of polymorphic transformation. From the presented data an explicit role is evinced for oxygen vacancy formation in the alumina matrix in the complex cascade of mechanochemical events determining the environmental resistance of the composite.

Abstract: Erbium-doped tellurite glasses show great potential for the fabrication of high-performance integrated optical amplifiers and lasers, thanks to their unique properties in terms of bandwidth and rare earth solubility. As a first step towards the development of smart multi-functional integrated optical circuits, the fabrication of multimode channel waveguides in a sodium-tungsten-tellurite glass, by using nitrogen ions implantation, has been recently demonstrated [1]. The effects of the ion implantation process, however, have not been fully clarified, and a deeper investigation would be necessary in order to optimize the process and to truly exploit the glass useful characteristics. We therefore report here the results of a broad optical, topographic, and structural characterization of tellurite samples irradiated with various doses of nitrogen ions, while keeping constant the beam energy at 1.5 MeV. Characterization techniques have included absorption and luminescence spectroscopy, modal (dark-line) spectroscopy, surface profilometry, scanning electron microscopy, cathodoluminescence spectroscopy and EDX analysis.

Abstract: Electro-stimulated piezo-spectroscopy (PS) can be quantitatively used for obtaining information about applied and residual stress fields piled up in ceramic materials and devices. PS experiments can be conducted in a field-emission-gun scanning electron microscope (FEG-SEM) equipped with a high spectral resolution cathodoluminescence (CL) spectrometer. Micromechanical information can be thus added to the microscopic crystallographic and chemical information already available in conventional SEM devices. Independent of the physical mechanisms behind CL emission, the spectral position of selected bands in ceramics is shown to possess high stress sensitivity. In addition, given the high scanning flexibility and spatial resolution of the electron beam, residual stress assessments can be performed on relatively large areas with significantly improved spatial resolution as compared with the more popular photo-stimulated PS approach (i.e., using a laser beam as the excitation source). In this paper, we first quantitatively characterize the stress dependence of the spectroscopic bands observed in ruby. Then, based on this knowledge, an application is shown of bi-dimensional residual stress mapping around an indentation print.