Phase TEM for biological imaging utilizing a Boersch electrostatic phase plate: theory and practice.
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.
Shiue
Jessie
J
Institute of Physics, Academia Sinica, Nankang 11529, Taipei.
Chang
Chia-Seng
CS
Huang
Sen-Hui
SH
Hsu
Chih-Hao
CH
Tsai
Jin-Sheng
JS
Chang
Wei-Hau
WH
Wu
Yi-Min
YM
Lin
Yen-Chen
YC
Kuo
Pai-Chia
PC
Huang
Yang-Shan
YS
Hwu
Yeukuang
Y
Kai
Ji-Jung
JJ
Tseng
Fan-Gang
FG
Chen
Fu-Rong
FR
D004867:Equipment Design; D005293:Ferritins / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D046529:Microscopy, Electron, Transmission / Q000295:instrumentation* / Q000379:methods*; D055672:Static Electricity
D005293:Ferritins