Abstract
In this paper we report quantitative measurements of the imaging performance for the current generation of hybrid pixel detector, Medipix3, used as a direct electron detector. We have measured the modulation transfer function and detective quantum efficiency at beam energies of 60 and 80keV. In single pixel mode, energy threshold values can be chosen to maximize either the modulation transfer function or the detective quantum efficiency, obtaining values near to, or exceeding those for a theoretical detector with square pixels. The Medipix3 charge summing mode delivers simultaneous, high values of both modulation transfer function and detective quantum efficiency. We have also characterized the detector response to single electron events and describe an empirical model that predicts the detector modulation transfer function and detective quantum efficiency based on energy threshold. Exemplifying our findings we demonstrate the Medipix3 imaging performance recording a fully exposed electron diffraction pattern at 24-bit depth together with images in single pixel and charge summing modes. Our findings highlight that for transmission electron microscopy performed at low energies (energies <100keV) thick hybrid pixel detectors provide an advantageous architecture for direct electron imaging.
Highlights
Direct electron detection can be achieved using the conventional film or various solid-state detection architectures including monolithic active pixel sensors (MAPS) [1] or variants of hybrid pixel detector technology [2,3] such as the Medipix3 sensors
We demonstrate, using the Medipix3 sensor that a thick silicon hybrid with coarse pixel geometry is ideal for low voltage Transmission Electron Microscopy (TEM) imaging up to 80 keV where the Modulation Transfer Function (MTF) is almost invariant and yields high Detective Quantum Efficiencies (DQE)
Our measurements of the MTF and DQE in single pixel mode using conventional knife edge and flat field image methods agree with trends already observed for the Medipix2 detector [8]
Summary
Direct electron detection can be achieved using the conventional film or various solid-state detection architectures including monolithic active pixel sensors (MAPS) [1] or variants of hybrid pixel detector technology [2,3] such as the Medipix sensors. MAPS technology forms the basis of many current direct detector systems that are widely applied for cryogenic transmission electron microscopy imaging in life sciences [4] and are beginning to be used in selected materials science applications [5] This family of detectors typically feature pixels with 6–10 μm lateral size, containing several transistors per pixel and with array sizes greater than 1 megapixel. Primary energies lower than 100 keV can provide greater contrast for thin biological samples [6] or the avoidance of knockon damage, for example in imaging 2-dimensional materials containing light elements [7] For these applications, the alternative architecture of hybrid pixel detectors may offer advantages. We demonstrate, using the Medipix sensor that a thick silicon hybrid with coarse pixel geometry is ideal for low voltage Transmission Electron Microscopy (TEM) imaging up to 80 keV where the Modulation Transfer Function (MTF) is almost invariant and yields high Detective Quantum Efficiencies (DQE)
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