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
- Requires complex staining process
- Whole system must be in a vacuum - so cannot view living specimens
- Image may contain artefacts
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- 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
- Less complex staining methods
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- 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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