Dresden 2020 – wissenschaftliches Programm
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O 100.10: Vortrag
Donnerstag, 19. März 2020, 12:45–13:00, REC C 213
Understanding chemical constrast in field ion microscopy — •Christoph Freysoldt, Shyam Katnagallu, Baptiste Gault, Michael Ashton, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40273 Düsseldorf
Field ion microscopy (FIM) was the first technique to image surfaces with atomic resolution. In FIM, rare gas atoms are ionized near the surface of a nano-sharp tip subject to a very high voltage. FIM has recently seen renewed interest as a 3D imaging technique for crystallographic features: by applying additional voltage pulses, the surface atoms can be slowly evaporated, revealing the atomic structure of the tip layer by layer. Today’s machinery of automated image processing allows then for a reconstruction of the tip’s atomic structure.
While the FIM imaging contrast (which strongly depends on field strength, geometrical, and electronic structure) is generally not well understood, recent combined FIM and atom-probe tomography experiments demonstrated and proved a high chemical contrast in a Ni-based model superalloy, where Re atoms are imaged much brighter than the Ni matrix. To explain this effect from a density-functional theory perspective, we exploit a hitherto unknown formal equivalence in the theory of electron tunneling between FIM and scanning tunneling microcopy (STM). The calculations show not only a significant enhancement of the local density of states above Re atoms in a Ni matrix, but also show that adsorbed rare gas atoms may act as ‘tunneling lenses’ that generally improve lateral contrast.