title: Tunable caustic phenomena in electron wavefields.
abstract: Novel caustic phenomena, which contain fold, butterfly and elliptic umbilic catastrophes, are observed in defocused images of two approximately collinear oppositely biased metallic tips in a transmission electron microscope. The observed patterns depend sensitively on defocus, on the applied voltage between the tips and on their separation and lateral offset. Their main features are interpreted on the basis of a projected electrostatic potential model for the electron-optical phase shift.
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany. Electronic address: a.tavabi@fz-juelich.de.
authors.forename: Amir Hossein
authors.initials: AH
authors.lastname: Tavabi
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Vadim
authors.initials: V
authors.lastname: Migunov
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Dwyer
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Rafal E
authors.initials: RE
authors.lastname: Dunin-Borkowski
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany; Department of Physics and Astronomy, University of Bologna, Viale B. Pichat 6/2, 40127 Bologna, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Pozzi
keywords: Caustics; Electron optics; Shaped electron beams; Transmission electron microscopy