High-Resolution Identification of Chemical States in Individual Metal Clusters in an Insulating Amorphous Polymer

The effectivity of cryo-scanning transmission electron microscopy-electron energy loss spectroscopy was demonstrated for nanoscale analysis of the cross-section of the Cu/polyimide interface. The nanoscale Cu/Cu2O/CuO layer structure at the interface was clearly observed for the first time. In addition, a Cu atom was identified, embedded in the polyimide matrix, and the average valence of diffusing Cu atoms or nanoclusters was determined using (cryo-)scanning transmission electron microscopy-electron energy loss spectroscopy. On the basis of these results, we have proposed a mechanism for the diffusion of Cu atoms in polyimide. To the best of our knowledge, this is the first report of the observation of a metal atom embedded in an insulating amorphous polymer.