Understand the benefits of frame-based and event-based detection technology, to choose the best hybrid pixel direct electron detector for your research needs.
When selecting the right hybrid pixel direct electron detection technology, it’s important to understand the benefits that a frame-based or event-based detector can deliver for your particular research needs. Our detectors, which utilise CERN’s Medipix3 and Timepix3 technologies, give you the flexibility to choose the best detection method for you.
The MerlinEM and CheeTah M3 detectors are frame-based detectors, whilst the CheeTah T3 provides event-based detection.
What are the differences between frame-based and event-based detection?
Hardware-based electron counting pixelated detectors offer many advantages to electron microscopy. Because the signal in these detectors is digitised in each pixel, the hardware electronics can be designed to read-out frames or events without additional noise. The decision as to which approach is better will depend on your specific experimental needs.
In general, frame-based readouts will be able to count hight intensity electron data within short time intervals, resulting in high dynamic range detection in each of the frames. An event-based detector will generate a data packet only when an electron strikes the chip. This can reduce the data rate for sparse imaging and offers additional information like time or energy stamping of the events for low-dose electron microscopy experiments.
Frame-based detection
- Will generate a constant data rate for a given dynamic range and frame rate (independent of beam current).
- Is mostly suitable for standard electron diffraction [1], STEM [2] and EELS [3] experiments, especially if a highly condensed beam is present, such as the central diffraction beam, CBED disk or zero-loss peak.
- Is most data efficient for standard and intense beam currents: Each electron will be counted in a given time interval and an overall 2D image of the experiment will be generated. When the number of events in the given interval is 2-3% or more of the number of pixels in the detector, the frame-based readout and storage is most data efficient.
Event-based detection
- Is useful for low-dose experiments, where a sparse signal is expected.
- Given the advantage of recording the exact time an electron strikes the detector, it can be used for fast STEM [4] scanning and correlations with excitation experiments in EELS [5].
- Is most data efficient for low-dose experiments: Each electron generates a packet of data which contains the position of the pixel, the timestamp of when it arrived and a length of time the event deposited energy took to readout. If the density of the electron beam is low, event-based mode is more data efficient.
References:
[1] Macpherson, Stuart, et al. “Local nanoscale phase impurities are degradation sites in halide perovskites.” Nature 607.7918 (2022): 294-300
[2] da Silva, Bruno César, et al. “Assessment of Active Dopants and p–n Junction Abruptness Using In Situ Biased 4D-STEM.” Nano Letters 22.23 (2022): 9544-9550
[3] Mallik, S., et al. “Superfluid stiffness of a KTaO3-based two-dimensional electron gas.” Nature Communications 13.1 (2022): 4625
[4] Jannis, Daen, et al. “Event driven 4D STEM acquisition with a Timepix3 detector: Microsecond dwell time and faster scans for high precision and low dose applications.” Ultramicroscopy 233 (2022): 113423
[5] Auad, Yves, et al. “Event-based hyperspectral EELS: towards nanosecond temporal resolution.” Ultramicroscopy 239 (2022): 113539.
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