Papers by Author: Andrea Leto

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.

Abstract: Electron-stimulated luminescence (cathodoluminescence, CL, henceforth) assessments can be quantitatively used in silicon-based optical devices for obtaining information about: (i) the residual stresses piled up during manufacturing; and (ii) the micro/nanoscopic structure of the device. In the present study, a quantitative characterization is presented from a micrometer to a nanometer scale using CL bands of some optically active defects existing within the nanostructure of optical devices. In particular, some CL bands, peculiar of oxygen-related defects in silica, have shown high stress sensitivity and thus were suitable for residual stress assessments. Knowledge of residual stresses can be quantitatively established from the examination of selected spectral shift characteristics (piezo-spectroscopic method). The correlation coefficient between stress and wavelength-shift of characteristic luminescence bands was systematically evaluated by stress calibrations. The piezo-spectroscopic approach shows promises as a valuable characterization tool, suitable for routinely inspecting micromechanical features and, thus, for optimizing low-loss, highquality optical devices.