Seminars Archive

Lattice defects as stress sensors in solids: Chemistry meets mechanics in the quantum world.

Abstract
Systematic assessments of electron-stimulated optical spectroscopy are presented for a number of oxide compounds. Emphasis is placed on spectral emissions from oxygen-vacancy sites (i.e., oxygen hole states) as intrinsic defects or extrinsically induced by charge compensation of sub-valent cations. The perturbation in the periodic electrostatic potential of a stoichiometric structure, due to the presence of oxygen vacancies, might induce highly localized perturbations of potential, which are responsible for valence band holes in the band gap of the unrelaxed defective structure. Cathodoluminescence data can consistently be rationalized according to notions of physical chemistry. Moreover, electron-stimulated emissions from oxygen hole states can be used as mechanical stress sensors, because the emission wavelength is related to the trace of the local stress tensor at the site of luminescence measurement. Accordingly, a new experimental method for micromechanics is proposed by which quantitatively assessing residual and applied stresses at the nanometer scale in the scanning electron microscope. This method has proved quite useful to the industrial world in various fields of applications, spanning from electronics to biomedical research.