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Types of electron microscope


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Types of electron microscope

  1. 1. Asad Rasheed 11-ARID-433
  2. 2. Type of Electron Microscope  Transmission Electron Microscope  Scanning Electron Microscope  Reflection Electron Microscope  Low-Voltage Electron Microscope
  3. 3. Transmission Electron Microscope  The Original Form of EM that uses the high voltage Beam of Electrons to create an image.  Its has Resolution power up to 0.5 angstrom (50 picometres).  Most Powerful for observing minute objects
  4. 4. Components
  5. 5. Mechanism  Electron Gun Produces Beam of 100 keV.  Anode and Cathode accelerate Beam.  Focusing occur by Electrostatic and electromagnetic lenses  Beam strikes the sample and pass through it.  After emerging out it carries information about Sample and magnify it by objective lens  Information can be analyzed by Screen or Film or CCD Cameras on LCD or monitor.
  6. 6. Advantages  TEMs offer the most powerful magnification, potentially over one million times or more  TEMs provide information on element and compound structure  Images are high-quality and detailed  TEMs are able to yield information of surface features, shape, size and structure  They are easy to operate with proper training
  7. 7. Limits of TEM  Spherical Aberration.  High Voltage can damage Sample.  Sample should be xtremely thin upto 100 nm.  Bio Samples are Dehydrated , chemically fixed, embedded in polymer resin to stabilize them.  Staining is required to highlight in order to achieve require image contrast.  Thinning of sample should be done upto 100 nm
  8. 8. Scanning Electron Microscope  SEM produces the image by scanning it with focus beam of electron.  Electrons interact with electrons in sample and convey information in form of signals to detectors. E.g. topography & sample surface.  SEM can achieve resolution better than 1 nanometer  Raster image focusing is used
  9. 9. Mechanism  When High energy Electrons strikes the surface, it lose energy by diff. mechanisms like heat, emission of low energy secondary electrons and high energy backscattered electrons.  X-ray or light emerges from sample that carries information on it.
  10. 10. Advantages  Its basically used for biological samples  It can scan the processes occurring on surface and tells about topography and composition.  Enable us to view without thinning dehydrating fixing the sample  Can scan bulk samples upto 2-3 cm which can not be examined by TEM.  View obtained is in 3D.  ESEM produce image of Wet, gas & Vacuumed Samples and biological samples.
  11. 11. Reflection Electron Mcroscope  Its is the fixation of Transmission and Scanning Electron Microscope.  Uses the Elastically Scattered Electrons for focusing the electron beam into a narrow spot which is scanned over the sample in a raster.  Raster is the rectangular pattern of image capture and reconstruction in television.
  12. 12.  TEM Sample forming processes are involved like thinning.  Highly contrasted mage is produces with higher focusing Difference  Rastering of beam occurs by focusing on rectangular area.  In REM Focusing action occurs before the beam strikes the sample but in TEM focusing action occurs after the striking  Also data is obtained in series image rather in parallel image form.
  13. 13. Low-Voltage Electron Mcroscope Microscope  As the Name suggests that it uses low voltage for scanning i.e. up to 5 KeV.  Higher Contrasting focus and good quality image are produces with good magnifying power better then TEM.  Pinpoint image are obtained on CCD Camera.  This type can be used as TEM, SEM, STEM.  No Staining Required
  14. 14. Comparison of LVEM & TEM of Rat Heart (Specific part)  LEVM @ 5 Kev TEM @ 80 Kev
  15. 15. Cont…  Present low voltage electron microscopes are capable of spatial resolutions of about 2.5 nm in TEM 2.0 nm in STEM and 3.0 nm in SEM.  Low voltage limits the maximum thickness of samples  It is about 100–200 nm in conventional TEM.  It decreases to around 20–65 nanometers for LVEM.
  16. 16. Thanks for being Patience