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 200nm

Magnification: 2000x

Illumination: Light

Glass lenses

Objects seen: frog's egg cells‚ cell wall‚ cilia‚ flagella‚ nucleus & other organelles etc.

Living specimen

Lower resolving power

Focus: 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?