Abstract
Hybrid pixel detectors (HPDs) have been shown to be highly effective for diffraction-based and time-resolved studies in transmission electron microscopy, but their performance is limited by the fact that high-energy electrons scatter over long distances in their thick Si sensors. An advantage of HPDs compared to monolithic active pixel sensors is that their sensors do not need to be fabricated from Si. We have compared the performance of the Medipix3 HPD with a Si sensor and a GaAs:Cr sensor using primary electrons in the energy range of 60–300 keV. We describe the measurement and calculation of the detectors’ modulation transfer function (MTF) and detective quantum efficiency (DQE), which show that the performance of the GaAs:Cr device is markedly superior to that of the Si device for high-energy electrons.
Highlights
The development of direct electron detectors (DEDs) over the past twenty years has opened up new experimental possibilities in electron microscopy, leading to significant advances in various fields [1,2]
We describe the measurement and calculation of the detectors’ modulation transfer function (MTF) and detective quantum efficiency (DQE), which show that the performance of the GaAs:Cr device is markedly superior to that of the Si device for high-energy electrons
This makes them highly effective sensors for capturing fast (1 ms) dynamics in a conventional transmission electron microscope (TEM) [10], and they show the potential to record processes at timescales of ≤ 1 μs [11,12]. Their ability to maintain a linear response even when subjected to high (≥ 1000 e−/pixel/s) electron flux means they are suitable for use in a variety of diffraction-based experiments [9]. They have been successfully used for micro-electron diffraction in structural biology [13] and 4D scanning transmission electron microscopy (4D-STEM), in both convergent and nano beam electron diffraction modes [14,15,16] in materials science
Summary
The development of direct electron detectors (DEDs) over the past twenty years has opened up new experimental possibilities in electron microscopy, leading to significant advances in various fields [1,2]. DEDs can be broadly divided into two categories: hybrid pixel detectors (HPDs) and monolithic active pixel sensors (MAPS) The latter have had great impact, substantially improving the resolution limit of cryogenic electron microscopy (cryoEM) at higher (≥ 200 kV) accelerating voltages [6,7]. HPDs with high-Z sensors should be capable of improved imaging performance for incident electrons across a wider range of energies, as the spatial distribution of the signal produced by high-energy electrons should be more localised [35] This would increase the versatility of HPDs and, combined with their advantages relative to MAPS detectors, they would have the potential to be near ‘‘universal’’ detectors for transmission electron microscopy, suitable for almost all applications at all accelerating voltages. We offer a comparison of their performance under uniform illumination and discuss some of the challenges associated with the use of high-Z sensors for imaging applications
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