Ultrafast EELS with Timepix3
In the past years EELS is often done with conventional detectors, such as CCDs or CMOS cameras. These conventional cameras work in frame mode, i.e. the electron beam on the sample can only move to the next probe position after the frame has passed. Therefore the minimum dwell time is constrained by the frame rate of the camera.
Modern cameras can provide frame rates up to several thousand frames per second, allowing dwell times in the range of 500 – 1000 microseconds.
Timepix3-based detectors are event-based, therefore they don’t have a limitation in frame rate. Every electron is immediately recorded as digital data. Timepix3 has a time resolution of 1.56 nanoseconds, allowing to move probe positions in the nanosecond range. In theory the CheeTah T3 EELS could perform EELS analysis with a dwell time in the nanosecond range. In reality the minimum achievable dwell time is limited by the scan coils of the TEM.
Yves Auad et al. demonstrated the benefits of CheeTah T3 EELS in an experimental setup (see graphics on the left). The solution is based on a combination of a scan device with the readout electronics of the CheeTah T3 EELS detector. This combination delivers a data stream consisting of the probe position (X, Y on sample) and the electron hit on the detector.
The data stream is then converted into a hyperspectral representation of the EELS spectrum at any given probe position (see picture below).
CheeTah T3 EELS
The CheeTah T3 EELS detector combines the benefits of modern hybrid pixel detectors (e.g. other Medipix3-based concepts or Dectris detectors) with the unique princple of time-resolved event-driven detection:
- High intrinsic amplification and thresholding enables electron counting
- Electron counting provides noise-free data
- Event-based detection leads to much smaller datasets compared to high-speed frame-based data, allowing live data preview
- Time resolution of 1.56 nanoseconds enables dwell times in the microsecond to nanosecond range – ideal for beam-sensitive samples