TRANSMISSION ELECTRON MICROSCOPY

Electron Microscope is scientific instrument that use a beam of highly energetic electrons to examine objects on a very fine scale

INTRODUCTION

DIFFERENCE BETWEEN OPTICAL MICROSCOPE AND ELECTRON MICROSCOPE

OPTICAL MICROSCOPE 1. Uses optical glass lens 2. Have low

magnification (500X or 1000X appx.)

3. Does not require vaccum for operation.

4. Small depth of field.5. Low price.

ELECTRON MICROSCOPE

1. Uses magnetic lens.

2. Have high magnification (10000X appx.)

3. Require vaccum for operation

4. Large depth of field.

5. High price.

Beam of electrons is transmitted through an ultra thin specimen,

An image is formed from the interaction of the electrons transmitted through the specimen,

The image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera

TRANSMISSION ELECTRON MICROSCOPE

ERNEST RUSKA

DEVELOPER OF TEM

T E M g i v e s I n f o r m a ti o n a b o u t ,

Topography : The surface features of an object Morphology: The shape and size of the particlesComposition: The elements and compounds that the object is

composedCrystallographic Information: How the atoms are arranged in the object

MAIN COMPONENTS OF TEM

The Lenses in TEMCondenser lenses(two)-control howstrongly beam is focused (condensed) onto specimen. At low Mag. spreadbeam to illuminate a large area, at highMag. strongly condense beam.

Objective lens-focus image (imageformation) and contribute most to the magnification and resolution of the image.

Four lenses form magnificationsystem-determine the magnificationof the microscope. Whenever themagnification is changed, the currentsthrough these lenses change.

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Sample Preparation

• Dehydration in alcohol• Embedding in resin• Semi-thin sections cut at 0.5 micron thick,

stained with toluidine blue• Selection of sample blocks• Ultrathin sections at 0.1 micron thick, stained

with lead citrate and uranium acetate

Principle of TEM

• Illumination - Source is a beam of high velocity electrons accelerated under vacuum, focused by condenser lens (electromagnetic bending of electron beam) onto specimen.

• Image formation - Loss and scattering of electrons by individual parts of the specimen. Emergent electron beam is focused by objective lens. Final image forms on a fluorescent screen for viewing

Beam and Specimen Interaction

Imaging in TEM

• Two principal kinds• Diffraction contrast imaging; BF and DF • Use either an non-diffracted or diffracted beam

and remove all other beams from the image by the use of an objective aperture.

• Phase contrast or high resolution imaging HREM use all of the diffracted and non-diffracted beams and add them back together. Phase and intensity to form a phase contrast image.

TEM Operation

• Tedious operation• Time consuming• Works in the dark• Photography required

Working of TEM

• High electron beam bombardment.• Lenses focus it onto the specimen• Electrons are used for image construction• Image is constructed by the transmitted

electrons• Thicker region occlude more beam

Working of TEM

• In areas in the object where these electrons encounter atoms with a heavy atomic nucleus, they rebound. • In regions where the material consists of lighter atoms , the electron are able to pass through.

TEM Uses in Biomedical

• Renal diseases• Typing of tumors• Muscle diseases• Skin diseases• Miscellaneous diseases

Advantages

• High resolution and magnification• Give information of Element and Compound• Detailed image obtain

Disadvantages

• Expensive• Images are black and white• Instrument in very large

Limitation

• Samples are limited to those that are electron transparent.

• Difficult to handle• Tricky sample preparation