Materials Science

DE cameras provide a unique combination of ultra-high resolution imaging with the flexibility and dynamic range demanded by a wide range of materials science applications such as high-resolution TEM (HRTEM), energy-filtered TEM (EFTEM), tomography, scanning TEM (STEM), electron holography, and more. No other direct detector is built for materials science like our DE cameras.

The Camera Really Does Matter

By eliminating the scintillator, our direct detection cameras provide unprecedented resolution and sensitivity. But is that really necessary for materials science? Absolutely! Many materials science applications rely on the ability of investigators to unambiguously detect high-resolution features in an image. Using a poor camera and blurry images makes the delineation of features ambiguous, and (even worse) many high resolution features may not be detectable at all. The camera really does matter.

MTF Comparison

An image of beamstop collected on a DE-12 Camera and a US4000 CCD at 200 kV under similar imaging conditions. Because the modulation transfer function (MTF) dramatically better with the DE camera, the edges of features recorded on the camera are much more distinct, yielding higher-resolution images.

Camera Comparison

An image of the same specimen recorded on a DE-12 Camera and a US4000 CCD, with similar sampling (detector magnification) and imaging conditions. Lattice spacing on the specimen are clearly visualized on the DE-12, while these features are too blurry to visualize on the CCD.

Highly Versatile

Electron Diffraction

Electron diffraction image of frozen-hydrated catalase crystal (unit cell of 173.5 x 69 Ångströms) collected on a DE-20 Camera System mounted on a JEOL 3200FSC (300 kV). The camera length was 200 cm. For data collection, the total exposure was 6 e2, acquired over 1 second with the camera operating at 32 frames per second. For processing, we discarded the first frame (which showed very blurry spots) and summed the next 22 frames, yielding an image corresponding to 4 e2 total exposure. The inset shows a zoomed view with the display brightness/contrast adjusted for visualization of the spots near the origin.

Our DE-Series Cameras are unique among direct detection cameras due to their high dynamic range and excellent performance at nearly any dose rate. As a demonstration of our versatility for a wide variety of TEM experiments, our DE cameras overcome the conventional wisdom that electron diffraction is not possible on a direct detector.

Not only does the high signal-to-noise ratio of our cameras accurately record the electron diffraction pattern, but our “movie-mode” acquisition also yields additional benefits: (1) We have observed that the diffraction spots appeared unstable (blurry) in the very first frame, so we ignored the first frame for further processing in order to boost the quality of the final image. (2) We could evaluate each frame and determine when the signal-to-noise ratio (SNR) of each diffraction spot was highest in order to “pick the exposure” after collecting data to yield the best possible diffraction pattern.

Low-Dose Imaging

One of the next frontiers in materials science is low-dose imaging. Many specimens are subject to various radiation damage effects under high-exposure conditions. In the ideal case, nearly all specimens in the TEM would be examined under low-dose conditions in order to minimize artifacts and/or specimen degradation due to these effects. However, low-dose imaging for materials science has been technically challenging due to the low sensitivity of scintillator-coupled TEM cameras. Our DE-Series Cameras allow users to overcome these challenges and collect brilliant, high-resolution images even under very low dose conditions.

Example: Electron Holography

In standard TEM imaging, the intensity of the recorded image is an inseparable combination of the amplitude and phase of the image wave. In contrast, electron holography uses the interference of two waves within the microscope: the incident, undeviated electron wave and the image wave. The resulting interference pattern can be processed using optical techniques to form optical holograms, so that the amplitude and phase components could be separately extracted.

Electron holography offers the unique capability to characterize the three-dimensional structure of TEM specimens, since observed phase changes (which are now disentangled from amplitude information in a hologram) is directly proportional to the local thickness of the material through which the electron beam is passing.

Low-Dose Electron Holography of Carbon Film

Electron holography of amorphous carbon film using a DE-12 Camera System installed on a Hitachi HF3300V TEM. (a) Hologram recorded in electron counting mode with a total dose of 4.3 electrons per pixel. (b) Recorded phase image showing the edge of amorphous carbon film. (c) Quantitative measurement of the thickness of the carbon film across the highlighted region of the phase image. Holographic reconstruction and image analysis was done using HoloWorks Software. Courtesy of Edgar Voelkl (Hitachi High Technologies America), Rodney Herring (University of Victoria), and David Hoyle (Hitachi High Technologies Canada).

Until recently, acquiring electron holograms always has been a technological challenge. On film, both the non-linearity and the modulation transfer function (MTF) impacted the quality of the hologram, as higher order sidebands are generated and higher frequencies are dampened. Although digital cameras are very linear up to at least 70% to their saturation, the MTF of almost every camera on the market drops to around 10% or below at the Nyquist limit and for sampling rates (pixels per interference fringe) s < 10, most MTFs are already below 50% at the location of the sideband (the main carrier of the holographic information). As a compromise, electron holograms are recorded highly oversampled and the images obtained from the holograms are often downsized as they contain a lot of empty information due to the oversampling. Our DE-Series Cameras are a revolutionary advancement for electron holography, approaching the theoretical limits of an ideal detector for this technique. The linearity, MTF, and array size of our cameras produce high-quality holograms without significant oversampling, to deliver a dramatically larger field-of-view. Additionally, the high sensitivity and per-electron signal-to-noise ratio of our direct detection cameras enable low-dose electron holography for the first time. This critical advancement allows researchers to probe the structure of specimens in an unperturbed state (without the deleterious effects of radiation damage).