TEM-Transmission Electron Microscopy

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Dear Er Manikandan could you pl send a copy of this powerpoint presentation to BsC agri students in KKM-email kumar.madurai@gmail.com

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TEM-Transmission Electron Microscopy:

TEM - Transmission Electron Microscopy 1 Present by V.MANIKANDAN ; BTE-08-027 B.Tech( Agricultural Engineering ) College Of Agricultural Engineering, Tamil Nadu Agricultural University, Kumulur, Tiruchirapalli-621712

Slide 2:


History :

History The first TEM was built by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolving power greater than that of light in 1933 and the first commercial TEM in 1939. 3

What Is A TEM?:

What Is A TEM? Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. 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. 4

Working principle:

Working principle 5

Slide 6:

6 TEM works like a slide projector. A projector shines a beam of light which transmits through the slide. The patterns painted on the slide only allow certain parts of the light beam to pass through. Thus the transmitted beam replicates the patterns on the slide, forming an enlarged image of the slide when falling on the screen. TEMs work the same way except that they shine a beam of electrons (like the light in a slide projector) through the specimen (like the slide). However, in TEM, the transmission of electron beam is highly dependent on the properties of material being examined. Such properties include density, composition, etc.


BASIC COMPONENTS OF TEM ELECTRON:- TEMs use electrons as "light source" and their much lower wavelength makes it possible to get a resolution a thousand times better than with a light microscope. where, h is Planck's constant, m 0 is the rest mass of an electron, E is the energy of the accelerated electron. 7

Electron source:

Electron source 8 The electron source consists of a cathode and an anode. The cathode is a tungsten filament which emits electrons when being heated. A negative cap confines the electrons into a loosely focused beam. The beam is then accelerated towards the specimen by the positive anode. Electrons at the rim of the beam will fall onto the anode while the others at the center will pass through the small hole of the anode. The electron source works like a cathode ray tube. 8

Slide 9:

9 Cross sectional diagram of an electron gun assembly, illustrating electron extraction Electron source

Electromagnetic lens system:

Electromagnetic lens system 10 After leaving the electron source, the electron beam is tightly focused using electromagnetic lens and metal apertures. The system only allows electrons within a small energy range to pass through, so the electrons in the electron beam will have a well-defined energy. Diagram of a TEM split polepiece design lens

Slide 11:

11 Aperture: A thin disk with a small (2-100 micrometers) circular through-hole. It is used to restrict the electron beam and filter out unwanted electrons before hitting the specimen. Magnetic Lens: Circular electro-magnets capable of generating a precise circular magnetic field. The field acts like an optical lens to focus the electrons.

Sample holder:

Sample holder 12 The sample holder is a platform equipped with a mechanical arm for holding the specimen and controlling its position. A diagram of a single axis tilt sample holder for insertion into a TEM goniometer . Titling of the holder is achieved by rotation of the entire goniometer


IMAGING SYSTEM 13 The imaging system consists of another electromagnetic lens system and a Screen The electromagnetic lens system contains two lens systems, one for refocusing the electrons after they pass through the specimen, and the other for enlarging the image and projecting it onto the screen The screen has a phosphorescent plate which glows when being hit by electrons. Image forms in a way similar to photography.

Slide 14:

14 Source : http :// en.wikipedia.org/wiki/Polio A TEM image of the polio virus. The polio virus is 30 nm in size .


Limitations There are a number of drawbacks to the TEM technique. Many materials require extensive sample preparation to produce a sample thin enough to be electron transparent, which makes TEM analysis a relatively time consuming process with a low throughput of samples. The structure of the sample may also be changed during the preparation process. Also the field of view is relatively small, raising the possibility that the region analyzed may not be characteristic of the whole sample. There is potential that the sample may be damaged by the electron beam, particularly in the case of biological materials. 15

The problem with biological matter:

The problem with biological matter Biological samples hate vacuum They have low intrinsic contrast They are very Radiation Sensitive 16 SOLUTION Frozen – hydrated samples Negative Staining


Conclusion Thus Transmission Electron Microscopy has attired and helped the various fields of science and is now inevitable tool for the development of mankind. 17

Slide 18:

18 Thank you

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