Scanning Electron Microscope | SEM

Working Principles: Produces images of a sample by scanning the surface with a focused beam of electrons. Electrons from the beam hit the surface of the sample and bounce off it as the secondary electron, backscattered electron etc. A detector registers these scattered electrons and turns them into a picture.
SEM Working flows.
  1. Electrons are fired into the machine. 
  2. The main part of the machine (where the object is scanned) is contained within a sealed vacuum chamber because precise electron beams can't travel effectively through air. 
  3. A positively charged electrode (anode) attracts the electrons and accelerates them into an energetic beam. 
  4. An electromagnetic coil brings the electron beam to a very precise focus, much like a lens. 
  5. Another coil, lower down, steers the electron beam from side to side. 
  6. The beam systematically scans across the object being viewed. 
  7. Electrons from the beam hit the surface of the object and bounce off it. 
  8. A detector registers these scattered electrons and turns them into a picture. 
  9. A hugely magnified image of the object is displayed on a TV screen.
Applications: 
  • Borders, Forms and Dimensions of Particles. 
  • Different Phases in a material. 
  • Composition of different phases by elemental analysis with EDX and WDX spectrometers. 
  • Micro dimensional impurities by point analysis (EPMA).



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