1. Context

Devices combining different materials and the materials themselves are heterogeneous at different scales, both intentionally and unintentionally, as a result of manufacturing processes and aging. Imaging techniques, such as optical and electron microscopy, scanning or transmission, are widely used, but give a limited view, due to their intrinsic resolution, the way they probe the material or the constraints of preparation for examination. For example, electron microscopies mainly see metallic elements and cations, and have more difficulty seeing lighter anions. The resolution of optical microscopy remains micronic; that of infrared microscopy is in excess of ten microns, and requires complex preparations. As Raman scattering probes matter via modulation of the vibrating chemical bond, this spectroscopy is directly sensitive to the nature of the chemical bond and the anions involved in it....