University of Cambridge > > Electron Microscopy Group Seminars > Bonding at screw dislocations in b.c.c. metals studied by electron energy loss spectroscopy

Bonding at screw dislocations in b.c.c. metals studied by electron energy loss spectroscopy

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With the ability to analyse materials at atomic resolution and perform high resolution electron energy loss spectroscopy (EELS) simultaneously at the SuperSTEM, it is now possible to examine screw dislocation cores. The nature of screw dislocations in transition metals has been a topic of primary interest for many years (screw dislocations have been implicated in the low temperature dependence of flow stress of bcc transition metals). We attempt to identify both the local electronic structural changes using EELS and lattice structural changes by atomic resolution imaging. In particular, we have investigated the cores of ¬Ĺ [111] screw dislocations in pure molybdenum (and mixed dislocations associated with an edge component). Simulations of the dislocation core have been used to generate theoretical EELS spectra by FEFF8 codes (we were careful to take into account the all-important d-bands and the effect of breaking local symmetry), which were compared with changes seen in the experimental spectra. Variations were observed in the spectra near the M4,5 energy peaks for molybdenum and show the presence of local electronic structural changes near the cores of dislocations, which could be attributed to the density of unoccupied states available. The changes at the core of dislocation, due to local symmetry breaking, do seem to alter the electronic structure.

This talk is part of the Electron Microscopy Group Seminars series.

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