Realization of a tilted reference wave for electron holography by means of a condenser biprism

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• 作者：Falk Rö ; der^a ; ^b ; ^{Falk.Roeder@tu-dresden.de" class="auth_mail" title="E-mail the corresponding author} ; Florent Houdellier^b ; Thibaud Denneulin^b ; Etienne Snoeck^b ; Martin Hÿ ; tch^b
• 关键词：Off-axis electron holography ; Condenser biprism ; Tilted reference wave ; Coherence ; Transmission cross-coefficient ; Dark-field electron holography
• 刊名：Ultramicroscopy
• 出版年：2016
• 出版时间：February 2016
• 年：2016
• 卷：161
• 期：Complete
• 页码：23-40
• 全文大小：5510 K

文摘

As proposed recently, a tilted reference wave in off-axis electron holography is expected to be useful for aberration measurement and correction. Furthermore, in dark-field electron holography, it is considered to replace the reference wave, which is conventionally diffracted in an unstrained object area, by a well-defined object-independent reference wave. Here, we first realize a tilted reference wave by employing a biprism placed in the condenser system above three condenser lenses producing a relative tilt magnitude up to 20/nm at the object plane (300 kV). Paraxial ray-tracing predicts condenser settings for a parallel illumination at the object plane, where only one half of the round illumination disc is tilted relative to the optical axis without displacement. Holographic measurements verify the kink-like phase modulation of the incident beam and return the interference fringe contrast as a function of the relative tilt between both parts of the illumination. Contrast transfer theory including condenser aberrations and biprism instabilities was applied to explain the fringe contrast measurement. A first dark-field hologram with a tilted – object-free – reference wave was acquired and reconstructed. A new application for bright/dark-field imaging is presented.