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 el ements with mixed valences, such as Mn and Co. Spatial mapping of the valen ce-state distribution of transition-metal elements is a challenge to existi ng microscopy techniques. In this letter, using the valence-state informati on provided by the white lines observed in electron energy-loss spectroscop y 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 filtered TEM. An optimum spatial resolution of similar to 2 nm has been achieved for two-phase Co oxides with sharp boundaries. This p rovides a new technique for quantifying the valence states of cations in ma gnetic oxides.