Post on 25-Feb-2016
description
IFFAT FATIMA
UOG
ELECTRON MICROSCOPE
Contents
• History• LM Vs EM • Electron microscope• Principle• Types of EM• Application & importance
History of Microscope1590-tube microscope by dutch glass maker 1665-Robert hooke’s microscope
Continued……………………………
1674-Antonee van leeuwenhookeTEM co-invented by Ernst Ruska (1931)
Main characteristics of microscope
• Resolution
Magnification
Light Microscope Vs Electron microscope
Comparison
Light microscope
Resolution: 0.2μm to 200nmMagnification: 2000xIllumination: LightGlass lensesObjects seen: frog's egg cells‚ cell
wall‚ cilia‚ flagella‚ nucleus & other organelles etc.
Living specimenLower resolving powerFocus: condenser lense
Electron microscope
• Resolution: 0.2nm• Magnification: 2‚000‚000x• Illumination: Electron• Electromagnetic lenses• Objects seen: orgenelles‚ proteins‚
viruses‚ small molecules etc.• Dead specimen• Higher resolving power• Focus: vaccum & magnetic lense
Electron microscope
• Electron microscope is a scientific instrument that uses a beam of energetic electrons to examine objects on a very fine scale.
Why electron beam?• Wave nature of particles
Types of Electron microscope
Transmission electron microscope
Instrumentation• Electron Source• Electromagnetic lense system• Sample holder• Imaging system
Working
• Emission of a high voltage beam of electrons.• Focusing of beam on specimen.• Transmission through the specimen.• Magnification of the image.• Recording of the image by fluorescent screen,
light sensitive sensor (camera).
TEM
Sample preparation
• Fixation• Rinsing• Post fixation• Dehydration• Infiltration• Polymerization• Sectioning
Applications
• Ultra-structure analysis• Crystal structure
Scanning Electron microscope• Emission of a beam of by an electron gun.• Passage of electron beam through the vacuum.• Focusing of beam down toward the sample.• Ejection of X-rays & es. From sample after hitting.• Collection of by detectors & conversion to a signal.• Transmission of signal to a screen/ final image
Scanning EM
Sample preparation
• Metals require no preparation• Non metals require coating of a thin layer of
conductive material.
Applications
• Medical & physical science• Semiconductor industry• Examination of a large specimen range.
Any Q?