Sub-100 nanosecond temporally resolved imaging with the Medipix3 direct electron detector

Gary W Paterson,Raymond J Lamb,Rafael Ballabriga,Dima Maneuski,Val O’Shea,Damien Mcgrouther

doi:10.1016/j.ultramic.2019.112917

Gary W Paterson, Raymond J Lamb + Show 4 more

Open Access

https://doi.org/10.1016/j.ultramic.2019.112917

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Abstract

Detector developments are currently enabling new capabilities in the field of transmission electron microscopy (TEM). We have investigated the limits of a hybrid pixel detector, Medipix3, to record dynamic, time varying, electron signals. Operating with an energy of 60 keV, we have utilised electrostatic deflection to oscillate electron beam position on the detector. Adopting a pump-probe imaging strategy, we have demonstrated that temporal resolutions three orders of magnitude smaller than are available for typically used TEM imaging detectors are possible. Our experiments have shown that energy deposition of the primary electrons in the hybrid pixel detector limits the overall temporal resolution. Through adjustment of user specifiable thresholds or the use of charge summing mode, we have obtained images composed from summing 10,000s frames containing single electron events to achieve temporal resolution less than 100 ns. We propose that this capability can be directly applied to studying repeatable material dynamic processes but also to implement low-dose imaging schemes in scanning transmission electron microscopy.

Highlights

Enabled by high coherence electron sources, advances in aberration corrected electron optics [1,2] and high stability power supplies, modern transmission electron microscopes (TEM) provide images with spatial resolution exceeding the interatomic spacing in materials
Ultramicroscopy 210 (2020) 112917 recently demonstrated that the single electron sensitivity of these detectors provides significant advantages for lower-energy (60-80 keV) TEM imaging [20] and 4-D scanning TEM (STEM) imaging [21], we demonstrate that around three orders of magnitude improvement in temporal resolution can be obtained when operating using continuous beams
We find that the pixel energy threshold may be used to improve the temporal resolution available in the single pixel mode of operation

Summary

Introduction

Enabled by high coherence electron sources, advances in aberration corrected electron optics [1,2] and high stability power supplies, modern transmission electron microscopes (TEM) provide images with spatial resolution exceeding the interatomic spacing in materials. The functional performance of advanced materials depends on their response to time changing conditions In this respect, conventional TEMs with continuous current electron sources are much more limited in providing insightful dynamic information. Large numbers of electrons are photo-emitted from the source, traversing the column as a single bunch [13,14,15] Across both UEM and DTEM techniques, the wide use of thermionic emitters leads to spatial and temporal coherence of the electron bunches being significantly lower than routinely obtained from conventional continuous electron sources [7,16]. This has limited time-resolved imaging to nanometre spatial resolutions. We present in-situ measurements of a dynamic electron beam process, demonstrating stroboscopic imaging in the sub-100 nanosecond regime in an unmodified TEM with a SNR well beyond the Rose criterion [22]

Medipix3 hybrid pixel architecture and temporal imaging

Dynamic illumination

Optimising time resolution

Sub-100 ns imaging

Summary and outlook