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mmc2021 Abstract Database

Expanding Performance and Usability of High-speed / Low-dose STEM Scanning

Expanding Performance and Usability of High-speed / Low-dose STEM Scanning

Session

Stream 1: EMAG - Soft and Hybrid Materials

Authors

Tiarnan Mullarkey (2, 3), Jonathan J.P. Peters (3), Clive Downing (1), Lewys Jones (3, 1)

Affiliations

1. Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN)
2. Centre For Doctoral Training in the Advanced Characterisation of Materials
3. School of Physics, Trinity College Dublin

Abstract text

Modern advances in scanning transmission electron microscopy (STEM), such as aberration correction, have meant that for many technologically relevant samples it is no longer our instrument that limits our resolution, but instead sample damage caused by the electron beam [1,2]. Reducing both the electron dose and the dose-rate by lowering the beam current and pixel dwell-time are key avenues to combat this which are available to all microscope operators. 

However, when imaging under these conditions, we find that artefacts such as signal streaking and detector afterglow begin to dominate our images [3]. Even in the absence of these artefacts the signal level in a single image frame is too low for the precision required in many studies, whilst navigating and focusing the image become near impossible. The problems then are severalfold; finding a way to eliminate these imaging artefacts, enabling navigating under ultra-low-dose conditions, and producing final data of a suitably high signal level.

Here we present a strategy for software and hardware retrofitting of the Gatan Digiscan to solve these issues in the following ways:

• Using a  refinement of our previous work [4], we pulse count electrons with a FPGA to create digital images live within Digital Micrograph to eliminate the previously described artefacts.
• Implementation of a live rolling live-average, such as those seen in SEMs, into Digital Micrograph to aid in navigating under low-dose conditions.
• Enabling the ability to capture a continuous buffer of image frames, allowing live playback of data, including those from before the operator began recording.

The combination of the above approaches natively into Digital Micrograph creates a powerful tool where the image acquisition capabilities of the STEM are pushed to their limits. Every electron is counted in the digital signal, and with the image buffer no data is wasted. These benefits are exemplified when imaging fragile specimens as the rolling live-average eliminates the need to go to higher electron doses to find a region of interest within the sample, and live playback of frames means we may be able to capture crucial dynamic events, if not rewind to before a point where a sample becomes too damaged. These benefits will be demonstrated through comparisons of analogue and digital data, and examples where the data buffer was used to find otherwise irretrievable data.

References

[1]       R. F. Egerton, P. Li, and M. Malac, Micron 35, 399 (2004).

[2]       A. De Backer, G. T. Martinez, K. E. MacArthur, L. Jones, A. Béché, P. D. Nellist, and S. Van Aert, Ultramicroscopy 151, 56 (2015).

[3]       J. P. Buban, Q. Ramasse, B. Gipson, N. D. Browning, and H. Stahlberg, J. Electron Microsc. (Tokyo). 59, 103 (2010).

[4]       T. Mullarkey, C. Downing, and L. Jones, Microsc. Microanal. 26, 2964 (2020).