Our flagship DE-Series direct detection cameras for electron microscopy are revolutionizing the industry, allowing investigators to achieve results they never before thought possible…
Transmission electron microscopy (TEM)  is a powerful technique for visualizing structure at nanometer or Angstrom resolution. However, TEM performance lags considerably behind its theoretical limit based on the physics of electron scattering, especially in cases requiring low-dose imaging. Multiple factors reduce the resolution and signal-to-noise ratio (SNR) of TEM images, including the microscope instrumentation, dynamic specimen processes (e.g., drift, beam-induced motion, charging, radiation damage, etc.), and inefficient electron detectors .
With the goal of overcoming many of these obstacles, Direct Electron introduced the first large-format Direct Detection Device (DDD®) in 2008, as the culmination of academic and industrial partnerships working through many generations of sensor development beginning in 2001 . As the pioneer in direct electron detection, our revolutionary DDD sensors were recognized with the 2010 Microscopy Today Innovation Award.
Principle of Direct Detection
Traditional TEM digital cameras use a scintillator to convert primary electrons in the microscope to photons before being detected by the imaging sensor. In contrast, the DDD directly detects image-forming electrons in the microscope without the use of a scintillator. The result is dramatically better resolution, signal-to-noise ratio, and sensitivity.
The secret to the DDD’s high performance is its thin sensing layer. Incident beam electrons pass through this thin layer leaving an ionization trail that is collected and either integrated or counted in pixels. Because the layer is so thin, lateral charge spread is minimized resulting in higher resolution than other detectors. Furthermore, image distortions are minimized since the DDD directly detects electrons without having to transfer signal through fiber-optic or optical lenses.
A second innovative feature of the DDD is its high frame rate, with no dead time between frames. This high frame rate delivers intrinsic dose fractionation during image acquisition, which can be exploited for motion correction, damage compensation, and other image processing techniques. High frame rate data acquisition also enables challenging TEM applications such as in situ TEM.
Direct Electron’s cameras are elegantly designed with careful consideration given to each feature and component to maximize user productivity.
As funding levels tighten, productivity and throughput become increasingly critical for successful investigators. Our DE-Series Cameras are uniquely designed to deliver the most flexibility and versatility, the most productivity-boosting features, and exceptional reliability.
|Direct Detector||Direct Electron||Alternative #1||Alternative #2|
|Pixel Size (μm)||6.0 - 6.5||14||5|
|Array Size||Various sizes up to|
8192 × 8192
|4096 × 4096|
(17% smaller than DE-20;
300% smaller than DE-64)
|3838 × 3710
(38% smaller than DE-20;
370% smaller than DE-64)
(CDS to reduce noise)
|Frame Shutter||Global or rolling||Rolling|
(Introduces gradients across images)
(Introduces gradients across images)
|Optimal Exposure Rate||Consistent performance at any exposure rate||Worse performance at low exposure rates||Only very low exposure;
< 3 e-/pixel/s is optimal;
at 10 e-/pixel/s performance drops ~30%
|Dynamic Range||> 400 e-/pixel/s||~160 e-/pixel/s||At ~60 e-/pixel/s quantum efficiency decreases ~60%|
Up to 30 fps, full frame;
1000+ fps for subarrays
Typically users may only save 7 frames
|40 fps transfer rate to computer|
|Survey Sensor||Integrated near-axis 2k × 2k survey sensor||Separately purchased and maintained||Separately purchased and maintained|
|Exposure Measurement||Integrated Faraday plate above the DDD sensor||None||None|
|Sensor Protection Shutter||Yes, patented||None||None|
|Retractable||Yes, mechanical||Yes||Yes, pneumatic|
|Sliding O-Rings||No, minimized vacuum spikes during insertion/retraction||???||Yes|
|Mounting Position||Film chamber (JEOL) or bottom-mount||Bottom-mount||Bottom-mount|
|Magnification Factor||Film chamber: 1.0×|
Bottom mount: ~1.4×
|Data Acquisition Software||Client-server model with multiple options:|
DE-StreamPix (in situ);
Open API for integration in custom software.
|Movie Processing Software||Flexible and open-source; patented algorithms||None||Proprietary|
Integrating and Counting Modes
The high speed and ultra high single-electron sensitivity of direct detection cameras enable two different modes of operation:
- Integrating mode – The total signal deposited on the detector by each electron is summed to form the final image. Due to its versatility and speed, this is the most popular mode of operation for a wide range of applications.
- Counting mode – Each incident electron is individually detected, isolated, and localized. In this mode, every incident electron is consistently represented by a single count in a single pixel (or sub-pixel). While this mode represents the highest possible performance, it is only effective in very low dose applications.
Our DE-Series Cameras allow users the choice between either integrating or counting mode.
Detector performance can be evaluated in several ways, including (from most fundamental to most practical):
- Modulation transfer function (MTF)
- Detective quantum efficiency (DQE)
- Carbon film Thon rings
- Actual experimental results
Modulation transfer function (MTF)
Modulation transfer function (MTF) is one of the most widely used scientific methods for describing optical performance. MTF measures the contrast (magnitude response) across all spatial frequencies up to Nyquist frequency (the theoretical resolution limit of the detector). Formally, the MTF is defined as the magnitude of the Fourier transform of the point spread function (PSF) of a detector. Note that the MTF describes detector performance under absolutely ideal experimental conditions, which are not always applicable in practice.
For TEM detectors, the MTF is typically calculated by collecting an image of a straight edge (such as the microscope’s beamstop), and then using software to calculate the edge spread function (ESF), which describes the amount of blurring apparent on the straight-edge image. The Fourier transform of the derivative of the ESF is the MTF.
Simply, the MTF curve can be thought of as resolution on the X-axis and contrast on the Y-axis (higher is better).
Detective quantum efficiency (DQE)
For TEM cameras, the Detective quantum efficiency (DQE) is probably the most well-known metric for assessing performance. DQE measures the combined effects of the signal (related to contrast, as described by the MTF) and noise performance of a detector. Similar to the MTF, the DQE describes detector performance under absolutely ideal experimental conditions, which are not always applicable in practice.
For TEM detectors, the DQE is typically calculated using three components: (1) the modulation transfer function (MTF), which describes the signal performance of the camera; (2) the normalized noise power spectrum (NNPS), which describes the noise performance of the camera; (3) the DQE(0) value, which describes the overall efficiency of the camera in accurately detecting each incident electron. The equation is: DQE = DQE(0) x MTF2 / NNPS.
Simply, the DQE curve can be thought of as resolution on the X-axis and relative signal-to-noise on the Y-axis (higher is better).
Carbon film Thon rings
While the MTF and DQE are useful metrics for evaluating the fundamental performance of a TEM camera, they neglect to account for many critical factors that affect practical camera performance. For example, a camera that requires a long exposure time will be much more affected by microscope and specimen instability. It is therefore instructive to examine detector performance empirically, under practical experimental conditions.
The power spectrum calculated of an underfocus image of a specimen with sufficient scattering power shows concentric Thon rings, which are an effect of the microscope’s contrast transfer function (CTF), which modulates the Fourier transform of the object in a defocus-dependent way. Even with a theoretical perfect detector, the signal-to-noise ratio (or relative intensity) of each successive Thon ring would decrease with spatial frequency, due to aberrations and imperfect coherence in the microscope. In practice, the detector used to record the image also damps the signal of the Thon rings. At some point, the combination of the microscope and the detector will dampen the signal of the Thon rings sufficiently that they disappear in the noise. The resolution limit of the microscope and detector may be approximated as the maximum spatial frequency where Thon rings remain visible.
To evaluate the performance of the microscope and detector together for collecting individual images, it is common to collect slightly underfocus images of amorphous carbon film. Carbon film has similar scattering power as biological macromolecules per unit area, but since carbon film is distributed evenly across the entire field-of-view, the total scattering power in the field-of-view is sufficient to visualize the resolution limit of the instrument.
The exceptional high-resolution performance of our DE-Series Cameras means the camera is no longer the primary limiting factor for TEM resolution. For example, the figure below shows very high resolution bright-field TEM imaging, with Thon rings out to 2.3 Angstroms resolution (92% Nyquist).
Actual experimental results
While fundamental metrics like DQE can be a helpful first step in evaluating camera performance, there is only one way to take into account the totality of a camera’s capabilities and limitations: actual experimental results. Whether you are after super high resolution, large volume imaging, or vizualization of dynamics, our DE cameras work efficiently to deliver the results you need, quickly.
One of the most challenging experiments in the field of electron microscopy is single-particle biological cryo-EM. Besides the difficulty in preparing good specimens, experimental factors such as radiation damage and beam-induced specimen motion make it very difficult to generate reproducible atomic models of biological macromolecules. The camera is absolutely critical in these experiments, since investigators must try to get the best possible data in order to push the limits of resolution. Our DE cameras have broken the 3 Ångström resolution barrier for single-particle cryo-EM, with as little as three days for data collection!
For more information about the specifics of each camera, please click the name of each camera in the list of available cameras below, or CONTACT US. We are happy to provide whatever figures or information you need to help you apply for funding, decide upon and purchase a camera, teach classes, etc.
Our current Direct Detection Device® sensors are the culmination of over a decade of continuing development, in partnership with academia and the US National Institutes of Health (NIH).
|Commercial Product(s)||Development Systems (Academic)||DE-12||DE-12||DE-12 (Gen2)||DE-20||DE-16,
|Pixel Size (μm)||20||5, 10, 20, 30||5||5||5||6||6||6||6.4||6.5|
|Array Size (pixels)||128 × 128||Various||550 × 512||1024 × 1024||560 × 460||4096 × 3072||4096 × 3072||4096 × 3072||5120 × 3840||4096 × 4096,
8192 × 8192
|Feature / Milestone||4 quadrants||4 sections||Single pixel design; MTF/DQE||Larger format; cryo-tomography||ADC per column; electron counting||Large format; commercialized||Faster; more radiation hardened||Backthinned; improved at 200 kV||Larger; reduced noise; improved MTF||Ultra-large format; improved SNR, dynamic range, and radiation hardness|
|Developer & Funding||University of California, San Diego|
|Direct Electron, LP
NIH RR024964 & NIH GM103417
As a result of our continuing development, we are proud to offer a range of direct detection cameras to the TEM field. Reflecting our focus on empowering users for a broad range of experiments, all of these cameras deliver the flexibility and versatility that a modern TEM facility demands. However, the features and specifications of each of these cameras are optimized for certain applications, to push your productivity to its limit.
For more information, please click the name of each camera below, or CONTACT US.
|Pixel Size (μm)||6.0||6.4||6.5||6.5|
|Array Size (Pixels)||4096 × 3072||5120 × 3840||4096 × 4096||8192 × 8192|
|Maximum Frame Rate with Full Array||40 fps (bin 1×)|
75 fps (bin 2×)
|32 fps||60 fps (bin 1×)|
120 fps (bin 2×)
|Integrated Survey Sensor||None||2k × 2k||2k × 2k||2k × 2k|
|Typical Applications||Economical general-use direct detection camera||Cryo-EM; DTEM; other low-dose applications||In situ TEM; materials science||Cryo-EM; high-throughput TEM|
 McMullan G, Faruqi AR, Clare D, Henderson R. “Comparison of optimal performance at 300keV of three direct electron detectors for use in low dose electron microscopy.” Ultramicroscopy 147, 156-163 (2014). View Publication.
 Li X, Zheng SQ, Egami K, Agard DA, Cheng Y. “Influence of electron dose rate on electron counting images recorded with the K2 camera.” Journal of Structural Biology 184, 251-260 (2013). View Publication.