Abstract
Resolution and coherence criteria in transmission electron microscopy are discussed, and a contrast transfer function (CTF) is derived for coherent spherical wave illumination. Assuming a disc source, the CTF for spherical wave illumination is identical to that for convergent illumination from an incoherent source. Assuming a Gaussian source, the CTF decays more rapidly for a spherical wave than for an incoherent convergent beam. The implications for high resolution microscopy using a field emission gun are considered and it is shown that, owing to both the reduced energy spread and the increased brightness of a field emission source, point-to-point resolutions of better than 1 A should be possible using existing technology. A simple method of incorporating the CTF in image calculations for perfect or imperfect crystals, which does not involve the usual Fourier transforming, is also given.
Original language | English (US) |
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Pages (from-to) | 125-142 |
Number of pages | 18 |
Journal | Optik (Jena) |
Volume | 58 |
Issue number | 2 |
State | Published - 1981 |
Externally published | Yes |
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering