Review of recent advances in spectrum imaging and its extension to reciprocal space.

Using examples from various domains of science, this review covers some recent developments in spectrum imaging (SI) using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Advanced multi-dimensional acquisition methods allow the acquisition of STEM-EELS data with other complementary data such as energy dispersive X-ray spectroscopy (EDS), cathodoluminescence and even combining them with reciprocal space analysis through a new method called diffraction imaging. This method allows real and reciprocal space information to be mixed to get a more complete description of the electron-sample interaction. The developments in SI data analysis such as multiple linear least-squares fitting, non-linear least-squares fitting and multivariate analysis allow for a robust extraction not only of each elemental distribution but also of each chemical phase in a sample through an intuitive computer-assisted method.