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Comparing Fourier optics and contrast transfer function modeling of image formation in low energy electron microscopy
K M Yu1, A Locatelli2, M S Altman1
1Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Ultramicroscopy
|April 4, 2017
Summary
Fourier Optics (FO) and Contrast Transfer Function (CTF) models for low-energy electron microscopy (LEEM) image formation were compared. While CTF is computationally efficient, FO is more reliable under certain conditions, especially with complex samples like graphene.
Area of Science:
- Physics
- Materials Science
- Microscopy
Background:
- Understanding image formation in low-energy electron microscopy (LEEM) is crucial for accurate interpretation.
- Fourier Optics (FO) and Contrast Transfer Function (CTF) are two theoretical models adapted for LEEM image formation.
Purpose of the Study:
- To compare the applicability and limitations of FO and CTF models in LEEM.
- To identify conditions where CTF may not accurately represent LEEM image formation.
Main Methods:
- Comparative theoretical analysis of FO and CTF models for LEEM.
- Evaluation of imaging errors, lens aberrations, and coherence effects on both models.
- Experimental validation using focal image series of suspended graphene.
Main Results:
- Both FO and CTF models account for imaging errors similarly but differ in image intensity calculation.
- CTF offers computational efficiency due to its simplifications.
- Lens aberrations and coherence significantly impact CTF validity, particularly with increasing defocus and complex samples.
- FO accurately modeled suspended graphene images where CTF failed.
Conclusions:
- The CTF approach is generally suitable for routine LEEM imaging but has limitations.
- FO provides a more robust framework for LEEM image formation, especially for challenging samples or specific imaging conditions.
- This study highlights potential pitfalls of CTF and guides the effective use of both FO and CTF for quantitative LEEM image evaluation.
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