MerlinEM, Hybrid Pixel Electron Counting Detector for Transmission Electron Microscopy

Date: 17.01.2023

MerlinEM, Hybrid Pixel Electron Counting Detector for Transmission Electron Microscopy

Tuesday 31st January 2023, 10:00am Theatre Auditorium, New Technologies & Techniques 2

Electron microscopy experiments with hybrid pixelated counting detectors started with a Medipix2 detector [1]. It was clear that direct electron detection and hardware-based electron counting can offer advantageous imaging capabilities. Subsequently, the next generation of the detector was commercialised as a MerlinEM detector by a collaboration between the University of Glasgow and Quantum Detectors Ltd. The MerlinEM can acquire micrographs with framerates more than two orders of magnitude faster than conventional CCD cameras. Moreover, this is possible without any dead time and readout noise which is very advantageous in transmission electron microscopy. This paper will demonstrate the capabilities of the MerlinEM detector in STEM, diffraction, and EELS.

The distribution of electrons for each point of scan in STEM contains a wealth of information that can be used to enhance established techniques like differential phase contrast (DPC) [2] but also to enable techniques like ptychography [3] or symmetry-STEM [4]. As an example of an enhancement for the DPC, Fig. 1(a) shows a comparison of conventional quadrant detector collected data and MerlinEM data. The diffraction contrast dominates the conventional method, whereas the post-processed 4D-STEM data reveals the quantitative magnetic information even in a complex multilayer sample [2].

The applications in diffraction and EELS utilise the exceptional dynamic range of the MerlinEM detector. As Fig. 1(b) demonstrates, it is possible to image the central diffraction peak with up to 24-bit dynamic range and still retain single electron sensitivity towards the edge of the diffraction pattern. Additionally in EELS, the absence of readout noise enables acquisitions of high core-loss information with the MerlinEELS detector. To demonstrate this, Fig. 1(c) shows an atomically sharp interface in LMO/STO sample by mapping Ti-K (5 keV) and a La-L3 (5.5 kV) EELS edges [5].

Figure 1. (a) annular quadrant and pixelated detector acquired DPC images of the same area. The maps of integrated magnetic induction in a complex multilayer polycrystalline sample demonstrate significant signal-to-noise enhancement using a pixelated detector (From [2] under CC 4.0 licence). (b) precession diffraction example acquired with MerlinEM detector, logarithmic scale demonstrating a high dynamic range of the detector [6]. (c) MerlinEELS example showing atomically sharp interface in LMO/STO interface for high kV core-loss EELS imaging [6].

[1] G. McMullan et al., Ultramicroscopy 107.4-5 (2007): 401-413.

[2] K. Fallon et al., Physical Review B 100.21 (2019): 214431.

[3] A. Strauch et al., Microscopy and Microanalysis 27.5 (2021): 1078-1092.

[4] M. Krajnak and J. Etheridge, Proceedings of the National Academy of Sciences 117.45 (2020): 27805-27810

[5] M. Gibert et al., Nano letters 15.11 (2015): 7355-7361.

[6] The author acknowledges Joaquim Portillo of NanoMegas SPRL for the precession diffraction dataset in Fig. 1(b), and Alexandre Gloter and Marcel Tencé of Université Paris-Saclay for the EELS dataset in Fig. 1(c).