To Monochromate or not to Monochromate: Balancing Electron Dose and Energy Spread Requirements
- Abstract number
- 37
- Presentation Form
- Submitted Talk
- DOI
- 10.22443/rms.mmc2021.37
- Corresponding Email
- [email protected]
- Session
- Stream 1: EMAG - Soft and Hybrid Materials
- Authors
- Frances Quigley (1, 2), Patrick McBean (1, 2), Peter O'Donovan (1), Dr. Lewys Jones (1, 2)
- Affiliations
-
1. School of Physics, Trinity College Dublin
2. Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin
- Keywords
Low Voltage Transmission Electron Microscopy, 2D materials, Image Simulation, Electron Dose, Energy Spread
- Abstract text
Low voltage transmission electron microscopy (≤80kV) has many applications in imaging 2D materials, which would be damaged at higher voltages (Klie, 2009). Once spherical aberration has been corrected for in a Transmission Electron Microscope (TEM), chromatic aberration may dominate and limit the ultimate resolution of the microscope. The chromatic (defocus) blur can be reduced by decreasing the energy spread of the impeding electrons. Options for reducing energy spread can include using a low energy spread electron source, such as a cold field-emission source, or installing an electron monochromator after the gun. However, while the installation of a monochromator produces the lowest energy spread, it results in a dramatic decrease in current of up to 97% for a FWHM of 25meV (Hachtel et al., 2018), which can reduce the signal to noise ratio of the image. The objective of our work was to assess this trade-off between energy spread and beam current on the resolvability of features in images.
Recent additions by our group to the Prismatic software (Ophus, 2017) allow the effect of chromatic aberration to be included while simulating TEM images. This is done by approximating the chromatic aberration with a defocus spread (Aarholt et al., 2020). Finite electron beam source size was simultaneously implemented in Prismatic, along with the addition of Poisson noise. Using Prismatic, we examine how low electron energy spreads and low electron dose affect the image quality of a 2D material for a spherical aberration corrected TEM. This will demonstrate the trade-off between energy spread and beam current on image quality. It also showcases the developments in Prismatic in simulating chromatic aberration, finite source size, and Poisson noise in TEM images.
Acknowledgments: This project was supported through funding from the Provost Project Award, Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), AMBER (Advanced Materials and BioEngineering Research), Science Foundation Ireland and the Royal Society.
- References
Aarholt, T., Frodason, Y. K., & Prytz, Ø. (2020). Imaging defect complexes in scanning transmission electron microscopy: Impact of depth, structural relaxation, and temperature investigated by simulations. Ultramicroscopy, 209(October 2019), 112884. https://doi.org/10.1016/j.ultramic.2019.112884
Hachtel, J. A., Lupini, A. R., & Idrobo, J. C. (2018). Exploring the capabilities of monochromated electron energy loss spectroscopy in the infrared regime. Scientific Reports, 8(1), 1–10. https://doi.org/10.1038/s41598-018-23805-5
Klie, R. (2009). Reaching a new resolution standard with electron microscopy. Physics, 2, 155425. https://doi.org/10.1103/physics.2.85
Ophus, C. (2017). A fast image simulation algorithm for scanning transmission electron microscopy. Advanced Structural and Chemical Imaging, 3(1), 1–11. https://doi.org/10.1186/s40679-017-0046-1