Make every electron count

Effortless Digital Imaging

The switch from analog to digital TV and radio ushered in a new era of signal quality – better resolution, bandwidth and no noise.
Scanning transmission electron microscope (STEM) imaging should be no different but decades on most STEMs still rely on analog detectors. While analog detectors are sensitive enough to capture individual electron interactions the process of sampling and analysing data post-hoc is expensive, noisy and time consuming.
Pulse is a real time signal processor that enables digital imaging without the expense of replacing your existing analog detector.

Plug and Play Electron Counting

Raw data capture includes noise, limits frame rates and requires vast quantities of storage for low quality data, not to mention the time and computing resources required to analyse that data.
Instead of integrating a signal level, Pulse analyses your raw detector data stream, counting and reporting every electron interaction as it occurs.
Better still, Pulse is truly plug and play. Splice it into your existing raw signal channel and data acquisition system and you’re ready to go with minimal downtime.

No More Noise

Because Pulse reports discreet electron counts instead of a signal level, noise and aliasing that reduce image quality are eliminated.
No more Gaussian thermal noise in low-dose imaging. No more smearing and streaking at high frame rates. Just accurate electron counts.

Why Pulse?

Currently, in many technology areas such as television, car radios or photography, the switch from analog to digital has delivered better performance and lower noise. Imaging in the scanning transmission electron microscopes (STEM) should be no different, but decades since its inception, analog detectors are still commonplace.

However, although these analog detectors are still commonly installed in nearly every STEM, these are actually highly sensitive sensors and are capable of detecting single electron signals [1]. Often this sensitivity is lost when acquisition systems perform simple integration on slow timescales. Recently, research has shown that if the signal is streamed at far faster sampling rates, and if the signal is process to count each electron event rather than integrating, a new digital imaging mode is obtained [2].

The Pulse signal processing unit from turboTEM performs precisely that function, streaming the raw signal from existing analog STEM detectors at high-speed and performing edge-detection based electron counting. The digital signal is then passed out to the existing data acquisition system on the microscope. By adding the ‘Pulse’ unit to existing systems, users can experience an upgrade to digital imaging with minimal additional hardware outlay.

The benefits of this new digital imaging mode are most obvious in two scenarios, fast scanning and low-dose. When imaging at high frame-rates such as those used for in-situ imaging (e.g. dwell times shorter than 2μs), individual afterglow streaks from each electron impact can begin to smear across several image pixels degrading spatial resolution. Alternatively, when imaging at very low doses, where single electron scattering is visible in each frame, the overall image quality can be dominated by Gaussian (thermal) noise from the microscope’s readout electronics. The Pulse system overcomes this by outputting a purely digital signal, with no thermal noise. This delivers, for example in dark-field STEM, a perfect zero signal in vacuum regions.

Community Feedback

As a microscope user, acquiring images using the Pulse counting box was very easy as the image acquisition integrated seamlessly into the very familiar Digital Micrograph software. The signal-to-noise ratio of the ADF images acquired using the pulse counting device, especially at low-dose, was excellent. I believe that this hardware has great potential to unlock the full potential of STEM imaging for beam-sensitive samples.

The current scintillator-type detectors in STEM, such as annular dark-field, potentially have single electron sensitivity. However, these detectors are still used as analog detectors. This digital pulse unit can directly count the number of electrons falling onto the detector, and the detector becomes a true electron counting detector: no more arbitral units in intensity-scaling. Such digital processing can significantly improve the signal-to-noise ratio, especially in low-dose conditions.

Frequently Asked Questions

The Pulse unit is connected to the analog outputs from the instrument’s existing detectors. This is most easily done by T-ing into the BNC connectors between these detectors and the acquisition unit (e.g. Digiscan). As the signal is read via such a “T”, the existing analog images still appear on the microscope as before and may be collected fully simultaneously with the new digital images.

The currently available Pulse implementation supports two channels in and two digital streams out. This means that the operator can collect, for example, HAADF and MAADF images with the current version. A four channel version is planned for availability from August 2023 – you can express your interest via this contact form.

The digital signals are transmitted using an industry-standard TTL digital line. This means that the Pulse unit is compatible with any acquisition system that is capable of recording digital ‘ones’. The Pulse system has been tested using the Gatan Digiscan 2* and pointElectronic ‘DISS6’ acquisition systems. The Pulse unit will also be forward compatible with any counting image acquisition system such as the Gatan DigiScan 3*.

* DigiScan is a trademark of Gatan Inc.

[1] Krause et al., Ultramicroscopy 161 (2016).

[2] Mullarkey et al., Microscopy & Microanalysis 27 (2020).