Scanning Strategies and Lens Designs for the (S)TEM
Prof. Lewys Jones
School of Physics - Trinity College Dublin, Advanced Microscopy Laboratory - CRANN - Dublin, turboTEM Ltd - Dublin
16:15 - 17:15 Tuesday 09 December 2025 TUG HS P2 A new state-of-the-art scanning TEM (STEM) instrument with accompanying cameras/spectrometers may exceed €5 million. As a result, many instruments cannot be updated as often as hoped, or entire regions or countries cannot participate at all.
As these flagship instruments are often shared across physical, chemical, and life science users, and as they are operated across a wide range of accelerating voltages, it can be challenging to optimise lens design for all cases. To address this, we have developed a user adjustable pole-piece (UAP) with variable gaps from 1.5 to 6.5 mm [1].
Annular dark-field imaging is perhaps the most popular imaging mode in the STEM because of its relatively easy interpretation. However, nearly all ADF detectors operate in an analogue mode. By operating at a low dose, and counting the electrons scattered to each detector using easily retrofitted hardware, we can realise a new digital STEM imaging mode with ideal linearity and zero dark noise [2]. Contrast is displayed proportionate to the varying number of events in a fixed dwell-time.
In order to improve the STEM frame-rate and/or reduce the accumulated beam-dose, novel scanning strategies can be adopted. This might include near-zero flyback followed by hysteresis correction [3], interlacing [4], serpentine scan paths, or physically redesigning the scan-coils.
An evolution of event-counting over fixed-dwell times, is to measure scattering rate by tracking the varying time to reach a fixed number of detected events. This trigger-event modulated probability observation (TEMPO) enables significant dose savings for fragile specimens or a frame-rate boost for in-situ studies [5].
Each of these three technologies can be retrofitted to existing TEMs to extend their performance, functionality or lifetime and example results will be presented.
References
1. Patrick McBean et al., Microscopy and Microanalysis, 28 (S1), 2636-2638 (2022).
2. Jon Peters et al., Nature Communications, 14 5184 (2023).
3. T Mullarkey et al., Microscopy and Microanalysis 28 (4), 1428-1436 (2022).
4. Jon Peters et al., Microscopy and Microanalysis 29 (4), 1373–1379 (2022).
5. Jon Peters et al., Science, 385, 549-553 (2024).
6. The authors acknowledge funding from SFI grants URF/RI/191637 and 19/FFP/6813, the AMBER centre 12/RC/2278_P2, and Enterprise Ireland grant UAP-4-TEM.
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