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Detective quantum efficiency of electron area detectors in electron microscopy.

McMullan G, Chen S, Henderson R, Faruqi AR - Ultramicroscopy (2009)

Bottom Line: Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology.In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated.We also show that part of the response of the emulsion in film comes from light generated in the plastic support.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB20QH, UK. gm2@mrc-lmb.cam.ac.uk

ABSTRACT
Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.

No MeSH data available.


Images showing the effects at different incident electron energies of both electron backscattering from the metal film holder and from light generated within the plastic film backing due to the passage of high energy electrons in Kodak SO-163 film. (a) Photograph of a film holder showing the cut-away region in the centre. The area where black ink was applied to the back of the sheet of film to suppress light reflection is indicated by the dashed box. (b) Image taken with 120 keV electrons showing the area around the cut-away film holder. The OD in the area where the ink was applied is  lower (the developed film is lighter in the area where the ink was applied). At 120 keV there is no sign of any effects from the film holder. (c) Image taken with 200 keV electrons showing a reduction in OD of  with the ink and a  reduction where there is no film holder and so no electron backscatter from the film holder. (d) Image taken with 300 keV electrons showing a  reduction in OD with the ink and a  reduction in OD from the removal of electron backscatter.
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fig9: Images showing the effects at different incident electron energies of both electron backscattering from the metal film holder and from light generated within the plastic film backing due to the passage of high energy electrons in Kodak SO-163 film. (a) Photograph of a film holder showing the cut-away region in the centre. The area where black ink was applied to the back of the sheet of film to suppress light reflection is indicated by the dashed box. (b) Image taken with 120 keV electrons showing the area around the cut-away film holder. The OD in the area where the ink was applied is lower (the developed film is lighter in the area where the ink was applied). At 120 keV there is no sign of any effects from the film holder. (c) Image taken with 200 keV electrons showing a reduction in OD of with the ink and a reduction where there is no film holder and so no electron backscatter from the film holder. (d) Image taken with 300 keV electrons showing a reduction in OD with the ink and a reduction in OD from the removal of electron backscatter.

Mentions: The effects at higher voltages of electron backscattering from the metal in film holders is well known and because of this the results shown above for Kodak SO-163 film at 300 keV were obtained with a film holder in which the metal backing had been cut away from behind the area of interest. A less well known effect comes from light generated by incident electrons, presumably in the plastic support of the film. These two effects are illustrated in Fig. 9 which shows digitised images at 120, 200 and 300 keV obtained using film holders with a rectangular window cut out as illustrated in Fig. 9a. To show the effects of light a rectangular area on the back of the film, as indicated in Fig. 9a, was coated with black ink from a dry-marker pen before exposure and removed prior to development. Putting ink on the front of the film, or on the film holder, has no noticeable effect which indicates that the light is being reflected from the bottom surface of the plastic. At 120 keV, there is no sign of electron backscatter from the film holder but the area with the marker pen has a slightly lower OD. At 200 keV the light effect is more marked and it is also possible to see a small contribution from electrons backscattered from the holder. At 300 keV the light effect increases slightly but the effect from electron backscatter is now much greater .


Detective quantum efficiency of electron area detectors in electron microscopy.

McMullan G, Chen S, Henderson R, Faruqi AR - Ultramicroscopy (2009)

Images showing the effects at different incident electron energies of both electron backscattering from the metal film holder and from light generated within the plastic film backing due to the passage of high energy electrons in Kodak SO-163 film. (a) Photograph of a film holder showing the cut-away region in the centre. The area where black ink was applied to the back of the sheet of film to suppress light reflection is indicated by the dashed box. (b) Image taken with 120 keV electrons showing the area around the cut-away film holder. The OD in the area where the ink was applied is  lower (the developed film is lighter in the area where the ink was applied). At 120 keV there is no sign of any effects from the film holder. (c) Image taken with 200 keV electrons showing a reduction in OD of  with the ink and a  reduction where there is no film holder and so no electron backscatter from the film holder. (d) Image taken with 300 keV electrons showing a  reduction in OD with the ink and a  reduction in OD from the removal of electron backscatter.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2864625&req=5

fig9: Images showing the effects at different incident electron energies of both electron backscattering from the metal film holder and from light generated within the plastic film backing due to the passage of high energy electrons in Kodak SO-163 film. (a) Photograph of a film holder showing the cut-away region in the centre. The area where black ink was applied to the back of the sheet of film to suppress light reflection is indicated by the dashed box. (b) Image taken with 120 keV electrons showing the area around the cut-away film holder. The OD in the area where the ink was applied is lower (the developed film is lighter in the area where the ink was applied). At 120 keV there is no sign of any effects from the film holder. (c) Image taken with 200 keV electrons showing a reduction in OD of with the ink and a reduction where there is no film holder and so no electron backscatter from the film holder. (d) Image taken with 300 keV electrons showing a reduction in OD with the ink and a reduction in OD from the removal of electron backscatter.
Mentions: The effects at higher voltages of electron backscattering from the metal in film holders is well known and because of this the results shown above for Kodak SO-163 film at 300 keV were obtained with a film holder in which the metal backing had been cut away from behind the area of interest. A less well known effect comes from light generated by incident electrons, presumably in the plastic support of the film. These two effects are illustrated in Fig. 9 which shows digitised images at 120, 200 and 300 keV obtained using film holders with a rectangular window cut out as illustrated in Fig. 9a. To show the effects of light a rectangular area on the back of the film, as indicated in Fig. 9a, was coated with black ink from a dry-marker pen before exposure and removed prior to development. Putting ink on the front of the film, or on the film holder, has no noticeable effect which indicates that the light is being reflected from the bottom surface of the plastic. At 120 keV, there is no sign of electron backscatter from the film holder but the area with the marker pen has a slightly lower OD. At 200 keV the light effect is more marked and it is also possible to see a small contribution from electrons backscattered from the holder. At 300 keV the light effect increases slightly but the effect from electron backscatter is now much greater .

Bottom Line: Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology.In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated.We also show that part of the response of the emulsion in film comes from light generated in the plastic support.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB20QH, UK. gm2@mrc-lmb.cam.ac.uk

ABSTRACT
Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.

No MeSH data available.