Röder F, Houdellier F, Denneulin T, Snoeck E, Hÿtch M. Realization of a tilted reference wave for electron holography by means of a condenser biprism.
Ultramicroscopy 2015;
161:23-40. [PMID:
26624513 DOI:
10.1016/j.ultramic.2015.11.004]
[Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Revised: 11/04/2015] [Accepted: 11/06/2015] [Indexed: 10/22/2022]
Abstract
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 (300kV). 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.
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