The MerlinEM Direct Electron Detector (DED), a pixelated detector ideal for applications such as 4D STEM and TEM dynamic imaging, offers rapid readout and improved signal to noise.

Overview of the MerlinEM

The MerlinEM detector is a unique type of technology in the field of electron microscopy. It is a detector based on a hybrid pixel architecture, which has revolutionised the X-ray community and is now transforming electron microscopy. Each sensor pixel is individually bump-bonded to an intelligent chip which uses threshold discriminators to distinguish electrons from the background, effectively eliminating all readout noise. This allows for integral mode imaging where multiple short exposure images are acquired and summed together. Uniquely, neighbouring pixels can communicate to mitigate charge-sharing effects, and this, combined with the direct detection of electrons, yields enhanced performance. As beam energies decrease toward 60 keV, the MerlinEM has been shown to provide near-ideal DQE and MTF detector response.


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  • Direct detection
  • Radiation tolerant
  • 30 - 300 keV detection
  • Up to 2000 fps 12 bit mode

MerlinEM converts incoming electrons directly into electron/hole pairs in the silicon wafer. CCD and some CMOS detectors need to convert the electrons into visible light as an intermediate step, thus losing information and increasing noise in the data collection. Additionally, MerlinEM is an event counting detector, which counts every incoming particle when there is enough energy deposited within the given pixel. This makes it an incredibly sensitive detector for electron microscopy purposes.

MerlinEM Readout Electronics

MerlinEM comes with everything you need to start collecting data. The MerlinEM readout electronics are based on a National Instruments PXI FPGA system with custom control electronics. This is a robust, extensible and well supported platform with a long product lifetime. It integrates a separate high performance industrial grade PC and FPGA card. The detector head is connected by a high density cable link that can be up to 10m long allowing a significant degree of flexibility in the mounting of the system. MerlinEM requires no external input other than mains power to run.

The MerlinEM in Action

Matus Krajnak, Application Scientist at Quantum Detectors talks you through our STEM interface for MerlinEM. With special thanks to the University of Glasgow and Dr Damien McGrouther for help with data collection and Merlin testing. Also thanks to Dr Magnus Nord for the Fe60Al40 sample.

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With the MerlinEM, we have been able to bring our existing microscope into the age of 4D-STEM. With the support from the Quantum Detectors team, the installation of the hardware and its integration with existing hardware was smooth. The provided readout and data acquisition software gives easy access to the most important acquisition modes out of the box and in combination with the flexible API, we are able to integrate the detector into more specific user cases. We are very excited to utilize this novel technology to tackle open questions in Materials Science!

Prof. Dr. Leopoldo Molina-Luna - TU Darmstadt

Applications for the MerlinEM

Quantum Detectors systems are designed with you in mind. We want to help you achieve results, here are some of the applications this system is capable of.


Modern fast framing electron detectors like MerlinEM allow practical imaging of a full distribution of electrons for each probe position in a scanning transmission electron microscope (STEM). The most common name of the technique is 4D STEM, however, scanned diffraction or momentum resolved STEM are also used.

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Diffraction Imaging and SPED

MerlinEM detectors offer unique opportunities for electron diffraction imaging. The simultaneous high dynamic range, high frame rate and ability to count single electrons massively expand the usefulness of this very established set of techniques. On top of this, the MerlinEM is radiation safe even at 300kV so there is no need to use a beam stopper.

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Ptychography is a subset of Coherent Diffractive Imaging (CDI) which uses a coherent energy source (in our case, electrons or X-rays) to illuminate a sample and retrieve the phase information on the sample from phase-retrieval analysis of the far-field diffraction pattern.

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Features of the MerlinEM

Rapid Gapless Readout and high dynamic range

Within each pixel are two counters, which can be used simultaneously to give gapless readout – whilst one counter reads, the other reads out. This unique approach is of particular importance for beam sensitive samples – there is no gap in time for readout so every part of the exposure to the sample is being read and recorded. This feature and the speed of the detector can be used to record gapless multiframe films of dynamic effects and it can be also used to collect diffraction sample tilt series by continuous rotation of the goniometer, without loss of any electron data to the read-out. Due to the electron counting approach of the detection system as well as the fully digital readout, MerlinEM adds zero noise allowing a Signal to Noise Ratio (SNR) within a single frame as high as 16.7 million to zero.

Region of Interest

The ROI Rows function allows a dramatic increase in speed of readout. The user can select how many Rows the software will read from the detector. The default value, 256, means that the whole chip will be read out. Selecting a different value will result in a rectangle image of N x 256 pixels where N can be N ∈ {4, 8, 16, 32, 64, 128}. The position of the Rows is fixed to the inner edge of the detector due to the architecture of the chip.  This mode can be used to significantly speed up the STEM acquisition. This feature is unique to MerlinEM detectors.

Effectively noise free

Each of MerlinEM’s pixels contains >1100 transistors within the 55 micrometer pitch, enabling intelligent processes to occur on chip. Each incoming electron is evaluated, and if it is above a user specified threshold energy level, the signal is counted. If it is not, then it reads as zero. This unique feature allows for noise-free data collection. This is unique to hybrid pixel technology and strongly differentiates it from analogue integrating detectors, such as indirect CCD technology or CMOS.

Dose sensitive imaging

The high signal to noise is not the only advantage when hardware electron counting is employed. With continuous imaging mode, our users can take one hundred 1 ms acquisitions (as an example) which should be exactly the same as one 100 ms long acquisition. This will allow the user to analyse how damage sensitive samples react to the electron beam and calculate the correct dose / frame time for your sample in a single exposure. In practice, summing the first 10 images will show exactly the same image as a 10 ms frame time, the first 20 images the same as a 20 ms frame time, etc. This is a very useful feature of the camera for radiation sensitive samples.


MerlinEM MIB data is in an open format. The various acquisition modes, as well as many other input parameters for the optimisation of the MERLIN system, are easily chosen by a user friendly Graphical Interface as well as remotely controlled via TCP/IP protocol, and Digital Micrograph. The MerlinEM software now includes an exciting opportunity to visualise 4D-STEM datasets in real time. Annular, bright field and DPC virtual detection is available in our new STEM interface.

The MerlinEM is compatible with third party data acquisition softwares, including LiberTEM-live, Instamatic and SerialEM.

Need some help?

Talk to our technical sales engineer about your requirements

Terence Giles

Dr. Terence Giles

Microscopy Sales Specialist

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Related Case Studies


Quantum Detectors at ePSIC

We speak to Dr Chris Allen about his experience of using the MerlinEM 4R at the electron Physical Science Imaging Centre (ePSIC), a national facility for aberration corrected electron microscopy.

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Quantum Detectors at NTNU

Quantum Detectors spoke to Prof. Ton van Helvoort and head engineer Dr. Emil Christiansen from NTNU in Norway to understand why they have chosen to put two MerlinEM detectors on their microscopes and how they have benefited their research so far, and to learn of their future plans.

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