Microscopes

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  • Created by: charlie_h
  • Created on: 01-06-16 16:54

TEM - transmission electron microscope

  • e~ beam is fired through the specimen, parts of specimen absorb e~ so appear darker than others and vice versa
  • Image can be produced on screen and can be photographed to give a photomicrograph 
  • Resolving power of 0.1 nm however this cannot always be achieved because...
    • difficulties preparing the specimen limit the resolution 
    • a higher energy e~ beam is needed which may destroy the specimen 
  • The main limitations of the TEM are...
    • Whole system must be in a vacuum - so can't observe living specimens 
    • complex staining process is required - even then image not in colour
    • specimen must be very thin
    • image may contain artefacts (something that remains from staining process that is not acctually part of the specimen)
    • image appears 2D unless multiple cross sections are taken to bulid up 3D image
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SEM - scanning electron microscope

  • Scans beam of e~ across the specimen and contour scatter the beam
  • Produces 3D image 
  • Resolving power of 20 nm
  • Limitations...
    • Requires complex staining process
    • Whole system must be in a vacuum - so cannot view living specimens
    • Image may contain artefacts
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Light microscope

  • Can only distinguish between two points if they are 200nm or more apart - limited by the relativly long wavelength of light
  • Can observe living specimens 
  • Cheaper
  • Less complex staining methods
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Unit conversions

  • m to...
    • mm X1000
    • um  X1,000,000
    • nm  X1,000,000,000
  • mm to...
    • m   /1000
    • um X1000
    • nm X1,000,000
  • um to...
    • m    /1,000,000
    • mm /1000
    • nm  X1000
  • nm to...
    • m    /1,000,000,000
    • mm /1,000,000
    • um  /1000
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