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MM: Fachverband Metall- und Materialphysik
MM 42: Electron Microscopy II - Advances in characterisation
MM 42.3: Talk
Wednesday, April 2, 2014, 12:30–12:45, IFW B
Probing atomic potentials on a sub-Angstrom scale by differential phase contrast — •Josef Zweck1, Sorin Lazar2, Bert Freitag2, Knut Müller3, Andreas Rosenauer3, Florian Krause3, Matthias Lohr1, Benedikt Bauer1, Andreas Pritschet1, and Johannes Thalmair1 — 1Physics Faculty, University of Regensburg, FRG — 2FEI Company, Eindhoven, NL — 3Institute for Solid State Physics, University of Bremen, FRG
Differential phase contrast uses a position sensitive detector to monitor minute deflections of the electron beam in a scanning transmission microscope (STEM). With today's instruments, the electron beam can be focused into probe diameters of 80 pm, which is sufficiently small to move the probe within a unit cell of a crystal between atomic positions. The beam is influenced by the local Coulomb scattering potential of the atom. The scattering potential gradient across the electron beam diameter can in a first approximation be considered to be proportional to the local electric field caused by the nucleus and screened by the electron cloud.
Therefore, measuring the electron beam's deflection one probes a quantity related to the local field distribution. We present first results, obtained from a GaN crystal, and using a FEI Titan cubed, equipped with a high brightness gun, monochromator, an image Cs corrector and DCOR probe corrector. We can clearly show that the electron beam deflection is not radially symmetric around Ga and N atoms, which may lead to a technique capable to probe local binding structures and even electronic charge densities in sub-Angstrom resolution.