title: Phase TEM for biological imaging utilizing a Boersch electrostatic phase plate: theory and practice.
abstract: A Boersch electrostatic phase plate (BEPP) used in a transmission electron microscope (TEM) system can provide tuneable phase shifts and overcome the low contrast problem for biological imaging. Theoretically, a pure phase image with a high phase contrast can be obtained using a BEPP. However, a currently available TEM system utilizing a BEPP cannot achieve sufficiently high phase efficiency for biological imaging, owing to the practical conditions. The low phase efficiency is a result of the blocking of partial unscattered electrons by BEPP, and the contribution of absorption contrast. The fraction of blocked unscattered beam is related to BEPP dimensions and to divergence of the illumination system of the TEM. These practical issues are discussed in this paper. Phase images of biological samples (negatively stained ferritin) obtained by utilizing a BEPP are reported, and the phase contrast was found to be enhanced by a factor of approximately 1.5, based on the calculation using the Rose contrast criterion. The low gain in phase contrast is consistent with the expectation from the current TEM/BEPP system. A new generation of phase TEM utilizing BEPP and designed for biological imaging with a high phase efficiency is proposed.
authors.affiliation: Institute of Physics, Academia Sinica, Nankang 11529, Taipei.
authors.forename: Jessie
authors.initials: J
authors.lastname: Shiue
authors.forename: Chia-Seng
authors.initials: CS
authors.lastname: Chang
authors.forename: Sen-Hui
authors.initials: SH
authors.lastname: Huang
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Hsu
authors.forename: Jin-Sheng
authors.initials: JS
authors.lastname: Tsai
authors.forename: Wei-Hau
authors.initials: WH
authors.lastname: Chang
authors.forename: Yi-Min
authors.initials: YM
authors.lastname: Wu
authors.forename: Yen-Chen
authors.initials: YC
authors.lastname: Lin
authors.forename: Pai-Chia
authors.initials: PC
authors.lastname: Kuo
authors.forename: Yang-Shan
authors.initials: YS
authors.lastname: Huang
authors.forename: Yeukuang
authors.initials: Y
authors.lastname: Hwu
authors.forename: Ji-Jung
authors.initials: JJ
authors.lastname: Kai
authors.forename: Fan-Gang
authors.initials: FG
authors.lastname: Tseng
authors.forename: Fu-Rong
authors.initials: FR
authors.lastname: Chen
mesh_terms: D004867:Equipment Design; D005293:Ferritins / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D046529:Microscopy, Electron, Transmission / Q000295:instrumentation* / Q000379:methods*; D055672:Static Electricity
chemical_list: D005293:Ferritins