Mapping electronic orbitals in the transmission electron microscope – ORBITEM

The direct observation of electronic states is elusive, although being responsible for chemical bonding and driving most physical, chemical and mechanical properties of materials. This project aims at breaking this barrier, and fostering electronic orbital mapping at the atomic scale, using electron energy-loss spectroscopy (EELS) in the transmission electron microscope (TEM). While a single proof-of-principle has been reported recently in a bulk material, the true interest of orbital mapping lies at crystal discontinuities, such as interfaces and defects, which affect the properties of materials. To achieve this goal, novel detection technology – direct electron detector – must be implemented in an EELS spectrometer to allow unprecedented gains in terms of noise level and acquisition speed, and unlock the door to mapping extremely weak signals like electronic states. It is worth emphasizing that the ORBITEM project addresses a true and defined scientific challenge, where access to the appropriate equipment is absolutely not sufficient. This project will contribute to advance the knowledge in an ambitious research topic, which has been seldom explored. We propose to develop new methodologies (data acquisition, processing, interpretation) to apprehend the problem at a spatial resolution necessary to probe chemical bonding at interfaces, and to support the interpretation of experimental data by the appropriate atomistic simulations. The theoretical background and methodology that will support the interpretation are fully established and will not be the limitation. The ORBITEM project has the potential to bring chemical bonding analysis to a whole new level, by mapping how atoms are bonded to each other, in real space, specifically at crystalline interfaces, providing crucial information not accessible by any other technique and at the limit of current numerical simulation capabilities.