Measurement of the localized electronic structure associated with bismuth segregation to copper grain boundaries

Grain boundaries in copper doped with small amounts of bismuth have been examined by spatially resolved electron energy loss spectroscopy (EELS). The electron energy loss or x-ray absorption near edge structure (ELNES or XANES) yields information on the bonding state of the probed atoms. A white line was detected near the threshold energy of the bulk absorption edge when the electron probe is located within 1 nm of the grain boundaries. This spectroscopic feature provides direct evidence that the grain boundary influences the local electronic structure and may have implications on how Bi embrittles the grain boundaries in Cu. Effects are only observed in those boundaries where the presence of Bi was confirmed using energy dispersive x-ray EDX spectroscopy. Furthermore, no evidence was found to indicate, within detection sensitivity limits, any co-segregation of oxygen to these boundaries.