Wednesday, December 26, 2018

Microscopic Techniques

Outline


1.Optical microscopy 

1. Conventional light microscopy, Fluorescence microscopy, confocal/multiphotonmicroscopy and Stimulated emission depletion microscopy

2.Scanning probe microscopy
Scanning tunneling microscopy (STM), Atomic force microscopy (AFM), Near-field scanning optical microscopy and others

3.Electron microscopy
Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Scanning transmission electron microscopy (STEM), Focus ion beam microscopy (FIB)

1. Optical Microscopy

Conventional Optical Microscopy

This is an optical instrument containing one or more lenses thatproduce an enlarged imageof an object placed in the focal plane of the lens
Resolution limit: submicron particles approaches the wavelength of visible light (400 to 700nm)

1. Transmission: beam of light passesthrough the sample
2. Reflection: beam of light reflectedoff the sample surface
e.g. Polarizing or petrographicmicroscope
Samples are usually fine powder or thin slices (transparent)
e.g. Metallurgical or reflected light microscope
Surface of materials, especially opaque ones


Polarizing Microscope

Polarizer & Analyzer


polorizing microscope
Only the light component whose vibration direction is parallel to the polarizer is permitted to pass through
Polarizer & Analyzer

Polarized light microscopy is utilized to distinguish between singly refracting (optically isotropic) and doubly refracting (optically anisotropic) media 


Principle of Polarizing Microscope




Crossed polars:       1.No sample  Æblack 
2.Isotropic sample   Æblack 
  3.Anisotropic sample   Æcolor

The interaction of plane-polarized light with a doubly refracting (birefringent) specimen to produce two individual wave components (ordinary rayand extraordinary ray) that are polarized in mutually perpendicular planes.

•Different velocities 
•Different propagation direction

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