There are two categories of microscopes based on the principle on which magnification is achieved, Light microscopes and Electron microscopes (EM). In Light or optical microscopes, magnification is obtained by a system of optical lenses using light waves. Electron microscope (EM) uses beams of electrons to produce images. In overall design, EM is similar to light microscopes with some differences (Refer: Electron Microscope vs Light Microscope)
Electron microscope was designed by Knoll and Ruska of Germany in 1932. There are two types of electron microscopes: TEM (Transmission Electron Microscope) and SEM (Scanning Electron Microscope)
Scanning Electron Microscope (SEM) vs Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
|
Transmission Electron Microscope (TEM)
|
Used to produce excellent images of the surfaces of cells and small organisms. Excellent for studying surface morphology of the organisms, cells or any suitable material under study
|
Used to study the ultra structure of the cell and its components. It can see objects as small as a protein molecule or even at nano level. Provides details about internal composition of cells or any suitable material under study
|
Electron beam scans over the surface of the sample
|
Electron beam pass through the sample
|
Based on scattered electrons or produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam
|
Based on transmitted electrons or produces images by detecting primary electrons transmitted from the sample
|
Comparatively low resolution than TEM; Resolution: 2nm(Average), 0.2nm (Special)
|
High Resolution; Resolution: 10 nm (Average), 0.5nm (Special)
|
Depth of field: High
|
Depth of field: Moderate
|
Magnifying power: 100,000X
|
Magnifying power: 5,000,000X
|
Specimen contrast: by electron adsorption
|
By electron scattering
|
Produces three-dimensional black and white images
|
Produces two-dimensional black and white images
|
Preparation technique: easy
|
Skilled, very thin sample is required
|
Preparation thickness: variable
|
Very thin
|
Specimen mounting: Aluminium stubs
|
Thin films on copper grids
|
Field of view: Large
|
Limited
|
Similarities between SEM and TEM
|
|
· Type of object : Non living
|
|
· Source of radiation: Electron
|
|
· Medium: High vacuum
|
|
· Nature of lenses: one electrostsastic and a few electromagnetic lenses
|
|
· Magnification Adjustment: Current in the projector lens coil
|
|
· Focusing: Current in the objective lens coil
|
|
Image credit:1) http://remf.dartmouth.edu/imagesindex.html 2) https://www.paldat.org/pub/Tilia_platyphyllos/109978
|
|
