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Detectors PowerPoint Presentation

Detectors

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Detectors

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  1. Detectors

  2. A laser scanning confocal microscope has many components including a way for several different lasers to provide excitation wavelengths and several separate detectors for various emission wavelengths

  3. One significant advance is how some systems separate the emission spectrum (signal) by wavelength and using slits sample those specific wavelengths using separate PMTs.

  4. The basic premise of an SEM is that signal produced from a scanned area of the specimen is displayed as an image with the exact same scan pattern on a CRT

  5. The scan pattern on the specimen is created by a set of deflection coils in the column that move the beam in a coordinated X/Y pattern. This is referred to as a scan or “raster” pattern

  6. Cathode Ray Tubeaccelerates electrons towards the phosphor coated screen where they produce flashes of light upon hitting the phosphor. Deflection coils create a scan pattern forming an image in a point by point manner

  7. Color CRTs usually have three separate e-guns, one each for red, green, and blue (RGB)

  8. Electron gun • Electron beam • Deflection coils • Phosphor screen with mask

  9. The scan generator coordinates the movement of the primary beam with the movement of the e-gun in the back of the CRT

  10. Magnification is accomplished by scanning a progressively smaller portion of the specimen and displaying the image on the CRT. Thus total magnification = square area of CRT divided by area scanned.

  11. The shadow produced in an SEM is determined by the position of the detector but the view is a “beam’s eye” view as if one were looking down the column

  12. A typical scintillator/PMT secondary-electron detector, often named an Everhart-Thornley (ET) detector after its two inventors

  13. In the case of an SEM or STEM the analog output of the detector (SE, BS, PMT, etc.) is sent directly to the framegrabber without the use of a camera. The spatial resolution being defined by the number of scanned points in the raster pattern.

  14. Backscattered-electron detectors installed below the SEM objective lens: (a) Annular-scintillator (Robinson) design and (b) solid-state (semiconductor) detector.

  15. Backscatter image (above) and secondary electron image http://pubs.usgs.gov/of/2001/ofr-01-0429/sem1/wtc01-36.html