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SUMMARY:Bonding at screw dislocations in b.c.c. metals studied by electron
  energy loss spectroscopy - Suneel Motru\, University of Liverpool &amp\; 
 SuperSTEM\, Daresbury
DTSTART:20080318T150000Z
DTEND:20080318T160000Z
UID:TALK9923@talks.cam.ac.uk
CONTACT:Dr Jonathan Barnard
DESCRIPTION:With the ability to analyse materials at atomic resolution and
  perform high resolution electron energy loss spectroscopy (EELS) simultan
 eously at the SuperSTEM\, it is now possible to examine screw dislocation 
 cores.  The nature of screw dislocations in transition metals has been a t
 opic of primary interest for many years (screw dislocations have been impl
 icated in the low temperature dependence of flow stress of bcc transition 
 metals). We attempt to identify both the local electronic structural chang
 es using EELS and lattice structural changes by atomic resolution imaging.
  In particular\, we have investigated the cores of ½ [111] screw dislocat
 ions in pure molybdenum (and mixed dislocations associated with an edge co
 mponent). Simulations of the dislocation core have been used to generate t
 heoretical EELS spectra by FEFF8 codes (we were careful to take into accou
 nt the all-important d-bands and the effect of breaking local symmetry)\, 
 which were compared with changes seen  in the experimental spectra. Variat
 ions were observed in the spectra near the M4\,5 energy peaks for molybden
 um and show the presence of local electronic structural changes near the c
 ores of dislocations\, which could be attributed to the density of unoccup
 ied states available. The changes at the core of dislocation\, due to loca
 l symmetry breaking\, do seem to alter the electronic structure. \n
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
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