Merlin for EM

An advanced HPAD direct detector development in the field of Electron Microscopy (EM).

The Merlin for EM Hybrid Pixel Array Detector (HPAD) is an advanced detector development in the field of Electron Microscopy, combining direct detection of electrons and rapid readout in a pixelated format ideal for applications such as 4D STEM and TEM dynamic imaging. 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 Merlin for EM has been shown to provide near-ideal DQE and MTF detector response.


Direct detection Noise-less detection of single electron events

Dynamic Range Up to 24-bit counting depth enabling 1:16.7 million intensity range in a single image, ideal for recording diffraction patterns

Effectively noise-free 2 threshold discriminators in each pixel means zero read noise and dark current

Charge summing mode Communication between pixels designed to mitigate charge sharing effects for maximising both DQE and MTF

Rapid readout Kilohertz frame rates in burst mode and zero deadtime in continuous mode offer more experimental flexibility than ever before, minimising effects such as sample drift, and enabling single shot and “pump and probe” dynamic experiments

Wide energy range and radiation tolerance Minimum 5 keV threshold making low energy EM imaging possible

Mount Static and retractable mounts available to fit many electron microscopes

See the datasheet for more details.


The Merlin readout electronics are based on a National Instruments PXI FPGA system with some additional custom control electronics.  This is a robust, extensible and well supported platform with a long product lifetime.  It integrates an embedded high performance industrial grade PC and FPGA card with 512GB dedicated RAM.  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.

As the Merlin contains an integrated PC, it requires no external input other than mains power to run.  In addition to its own intuitive graphical interface, the system also implements a TCP/IP based remote control function that allows easy integration with a users control systems.


Medipix3 is a was developed by an international consortium including CERN, DESY, ESRF and Diamond and provides a range of features that are unavailable in other hybrid pixel detectors, including continuous read-write, colour mode, 12 or 24 bit well depth (approx 17 million counts per well) mode selection and all in 55µm pitch pixels.


When an electron strikes near the edge of a pixel, the resulting charge may leak into neighbouring pixels by diffusion, sometimes below the threshold level.  In some detector systems this information is mis-interpreted as lower energy electrons on the pixels.  Merlin is different and makes use of Medipix’s Charge Summing Mode.  Merlin recognises that this information belongs to one event on one pixel rather than up to 4 weaker events on 4 pixels.  By reconstructing the event using the diffused charge data, Merlin ensures an accurate reading of the event giving improved results quality.

2016-11-24_TEM-Pix_Single_Fixed_with_Additional_Cover_retracted_Render_02 (1)

Image credit: University of Glasgow


Merlin, developed by Diamond Light Source, is a robust and versatile system built around the Medipix3 ASIC. It is designed with the high performance and reliability standards required by synchrotron beamlines and other industrial and large scale scientific applications.

Merlin for EM is an adaptation of the Merlin for electron microscopy use, developed in conjunction with the University of Glasgow.


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