Classical TEM Imaging using negative film materials has been partly replaced by CCD technologies in the past 10 years. While film still produces highest definition images on a big field of view it shows strong limitations in dynamics and linearity. CCD-cameras, which on one hand have the advantage of producing direct digital images, on the other hand only cover a limited area at moderate dynamic range. A third alternative, i.e. Digital Imaging Plate Technology, although known for some time, is now available and affordable for broad use and overcomes the limitations of both technologies: The results are high definition and digital images.
Imaging Plates are nearly ideal electron detectors that give you highest quality digital Images. DITABIS Imaging Plate Technology enhances your results with all the benefits of digital imaging. Exploring the advantages of the Imaging Plate Technology, best results are obtained in resolution, linearity, sensitivity, dynamic range and DQE.
Benefits of Imaging Plate Technology
- Highest definition images on a big usable area
The Imaging Plate reader micron reads with a pixel size of 15μm up to 50μm, (different instrument versions available) and can use the full area of 80x90mm resulting in images with up to 6000x5000 Pixel. Compared with CCD cameras that have pixel sizes in the same range, the detected area of the Imaging Plate is about the tenfold of the CCD. The definition of the images is excellent. This is shown with the Point Spread Function (PSF) that shows the coupling of neighboring pixels. With the Imaging Plate, the information is highly localized within the pixel. This results in a high Modulation Transfer Function (MTF). At highest transmission frequency (one pixel bright, next dark) the modulation is still as high as 38% (25μm reader device).
- High dynamic range
The response of the Imaging Plate is linear to the applied electron dose in a broad dynamic range. The Imaging Plate reader micron digitizes the image data with 16 bit or 20 bit allowing a contrast of over 6*104 or 106. Negative-film in comparison has only 1*102 linear range. Thus more information can be extracted from one exposure, there is no need for multiple exposures. Diffraction patterns of a widely varying range of intensities can be observed in a single exposure and displayed in one image.
- Unrivalled sensitivity
Imaging Plates do not need a minimum dose like negative-film, nor is there a significant readout noise like with CCDs. This makes the Imaging Plate the ideal detector for low dose imaging applications. Observing most beam sensitive specimens the electron dose can be far reduced, compared with negative-film (IP is about ten times more sensitive than negative-film). At even lower doses usable images can be obtained, only the quantum noise increases. So you expand the usable dose range for sensitive samples.
- High DQE
The inherent amplification of the Imaging Plate and a newly designed detector system guarantees a high Detection Quantum Efficiency (DQE) for electrons, even at lowest signals. This means, that a high percentage of the electrons that hit the plate are detected, resulting in high sensitivity and low noise of the Imaging Plate detection system.
- Variable Pixel Size
The latest member of DITABIS’ Imaging Plate reader family, the micron vario features a selectable pixel size from 15 to 50μm in 8 steps. Besides the enhanced resolution, this allows to optimize the readout to your application, generating only as much data as you need and gives you flexibility for all your applications. There are also fixed pixel size instruments available for 17.5 and 25μm.
- True Linearity
The luminescence signal emitted from the plate while reading is directly proportional to the exciting electron dose. Therefore the data are directly numerically quantifiable. For comparison: The EM negative-film has a sigmoid nonlinear characteristic that makes quantification difficult. Due to the linear signal intensity of micron, quantifying the electron dose for diffraction patterns (EELS spectra and HREM images) is far more accurate than with negative-film.
- Digital image data is instantly available
The DITABIS Imaging Technology is digital with no intermediate stages like chemical development. The data are digitized during the reading process and are available directly after readout. This gives you all advantages of the modern digital world: Visualization with zooming and contrast setting at the screen, printing on any PC printer, quantification and archiving on various media.
Imaging Plate Technology is an economical way to produce high quality images. As the plate is reusable for up to 1000 times the cost per shot is very low. No chemicals or other darkroom equipment is needed, reducing waste and labor. The proprietary Imaging Plate Technology eliminates time needed for film processing and enlargement, freeing more productive time for your research. The images are instantly digitally available on your computer for evaluation and further processing of the data.
As the reader is not directly linked to the TEM, one micron instrument can serve multiple different TEMs. Regardless of which TEM you use the Imaging Plate fits to every microscope. In a typical lab with 100 shots per day the prime costs of a DITABIS reader are paid off in a year.
Imaging Plate Physics
The Imaging Plate is a flexible electron detector, where an active layer of tiny crystals locally store high energetic radiation. The storage crystals are made from doted barium fluoro-bromide embedded in some blue colored resin. The electron irradiation excites the crystals in their luminescence center to a semi-stable state. The image information, formed by this excitation is stable for many hours and decays within days. By an illumination with red laser light, the crystals are excited again and stimulated to release the stored information as blue luminescence signal. The amount of blue light released depends on the first excitation with electrons and is a direct measure of the electron dose. As this is a physical process it is fully reversible without degradation, so the Imaging Plate can be reused many times. By exposing to white light for a period of 10 to 15 minutes all excitation is released and the plate is ready to be exposed again. The active layer is protected by a thin polymer layer on top. It is supported by a polymer layer and a thin metal (antimagnetic) base that gives its mechanical stability. (See figure top right) As the excitation is stored within the crystal luminescence centers the number of available storage cells is virtually unlimited. For this reason the plate is not saturated in a TEM. Only the readout device limits the dynamic range. During exposure the electron enters the plate and deposits its energy by exciting a large number of crystal centers. The lateral electron scattering is limited to a few micron so the information is highly localized. The blue color of the resin absorbs the red laser light while perfectly transmitting the blue luminescence signal so lateral scattering of the readout light is greatly reduced.
These features make the Imaging Plate an ideal electron detector:
- High Sensitivity as one electron produces a number of photons. So virtually every single electron can be detected
- High dynamic range as there is no saturation
- Sharp Images as the information is highly localized (low crosstalk)
- Large detection area (80x90 mm)