It is a topic about microscope

1. Microscopes
• A microscope a an instrument used to see small objects that can magnify their image via
connected lenses
• There are two types of microscopes:
◦ Optical microscopes (4 types)
◦ Electron microscope (2 types)

2. Some Principles of Light Microscopy
o Resolution: the ability to distinguish two adjacent objects as separate and distinct
◦ Resolution is determined by the wavelength of light used and numerical aperture of lens
◦ Magnification is not the limiting factor in the ability of seeing small things but also we need a
good resolution which is the ability to distinguish two adjacent objects

3. Magnification can be increased with out limit but resolution cannot because it is the function of
physical properties of light.
Light microscopy limits resolution is about 0.2µm , electron microscope resolution is greater
than of light microscope .
Some Principles of Light Microscopy

5. Electron Microscopy
Electron microscopes use electrons instead of photons(visible light) to image cells
and structures.
Electromagnets function as lenses in EM , whole system operates in a vacuum.
EM are fitted with cameras to allow a photograph to be taken
Two types of electron microscopes:
◦ Transmission electron microscopes (TEM)
◦ (need thin section)
◦ Scanning electron microscopes (SEM)
◦ Coat with heavy metal

6. Optical microscope
 Use light to visualizing the sample
• Wavelength range λ= 500 nm
• Low magnification
• Use glass lenses i.e. Eye piece and
Objective lens
• Not required vacuum chamber
• Form 2-D image
Scanning electron microscope (SEM)
 Use electron beam (EM waves) to
visualizing the sample
 Used to study the surface study of the
material/sample i.e. shape, size etc.
 Wavelength range λ=0.2 nm
 High magnification
 Use EM lenses i.e. condensing lens and
objective lens
 Required vacuum chamber
 Form 3-D image also

7. Transmission electron microscope (TEM)
 Use electron beam (EM waves) to visualizing the sample
 Used to study the inner structure of the sample
 The ultrathin sample is needed
 Wavelength range λ=0.2 nm
 high magnification
 Use EM lenses i.e. condensing lens and objective lens
 required vacuum chamber

8. Effects of increasing voltage in electron gun:
Resolution increased ( decreased)
Penetration increases
Specimen charging increases (insulators)
Specimen damage increases
Image contrast decreases

10. Figure2.9
Electron
source
Evacuated
chamber
Sample
port
Viewing
screen
© 2012 Pearson Education, Inc.

11. SEM images (Nanofibers)
(a)
(c)

12. TEM images (Nanotubes)