Mapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron Microscopy

The properties of transition-metal oxides are related to the presence of elements with mixed valences, such as Mn and Co. Spatial mapping of the valence-state distribution of transition-metal elements is a challenge to existing microscopy techniques. In this letter, using the valence-state information provided by the white lines observed in electron energy-loss spectroscopy in a transmission electron microscope (TEM), an experimental approach is demonstrated to map the valence-state distributions of Mn and Co using the energy-filtered TEM. An optimum spatial resolution of 2 nm has been achieved for two-phase Co oxides with sharp boundaries. This provides a new technique for quantifying the valence states of cations in magnetic oxides. Many physical and chemical properties of inorganic materials are determined by the elements with mixed Valences in the structural unit,1 by which we mean that an element has two or more different valences while forming a compound. Transition-and rare-earth-metal elements with mixed valences are unique for initiation of electronic, structural, and/or chemical evolutions. We have demonstrated previously the valence states of Mn an