Microscopes

TRANSMISSION ELECTRON MICROSCOPE 

Consists of:

• Electron gun - produces beam of electrons
• Condenser electromagnet - focuses beam onto specimen
• Screen - where image is shown and can be photographed (photomicrograph)

How image is seen:

• Beam of electrons passes through thin section of specimen
• Specimen absorbs electrons - appear dark
• Electrons pass through specimen - appear bright

Limitations:

• Vacuum required - can't observe living things 
• Complex 'staining' process is needed
• Extremely thin specimen 
• Artefacts can be seen - things that are seen as a result of preparation

SCANNING ELECTRON MICROSCOPE 

How image is seen:

• Electrons do not penetrate
• Beam of electrons directed onto surface from above 
• Beam is passed back and forth in a regular pattern
• Electrons are scattered 
• Scattering depends on contours
• A 3D image can be made on a computer

Limitations: 

• Vacuum required - can't observe living things 
• Complex 'staining' process is needed
• Artefacts can be seen - things that are seen as a result of preparation