Simultaneous STEM imaging and electron energy-loss spectroscopy with atomic-column sensitivity

Abstract

IMAGING with the scanning transmission electron microscope (STEM) has recently gained in resolution from the use of the annular dark-field (ADF) method1,2, which produces a signal that is highly sensitive to atomic number. There is a possibility that electrons from the probe beam that are scattered inelastically might be collected to provide a spectroscopic signal containing information about atomic bonding and electronic structures this is the basis of the standard electron energy-loss spectroscopy (EELS) technique. Browning et al.3,4 have shown recently that an EELS signal from absorption of atomic core levels can be used, in con-junction with ADF imaging, to obtain information about chemical composition at atomic resolution. Here I report the use of a similar approach to resolve the different bonding states of silicon atoms (Si0, Si2+ , Si4+) across a Si0SiO2interface. The oxidation state of individual columns of unit cells, containing pairs of silicon atoms, can be resolved with this method, allowing the structure of the interface to be characterized in great detail. © 1993 Nature Publishing Group.