Instrumentation of Transmission electron microscope .............. ,,,.pptx

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1. Transmission Electron Microscopy Presented To : DR MANZAR ZAHRA Presented By : Rimsha

2. Table of content Introduction Principal Sample Preparation Instrumentation Working Application Advantage Disadvantage

3. Introduction A Transmission Electron Microscope is a microscopy technique which a beam of electron is transmitted through a specimen to form a image The specimen is most often an ultra thin section less than 100nm thick or a suspension on a grid An image is formed from the interaction of the electron with sample as the beam is transmitted through the specimen The image is magnified and focused onto a imaging device such as Fluorescent screen a layer of photographic film , or a senor Such as scintillator attached to a Charged Coupled device (CCD)

4. Sample Preparation Tissue sectioning : thinned to less than 100 nm on a ultramicrotome Fixation : fixed with chemical products (Glutaraldehyde) Rinsing and Staining : treated with heavy metal compounds ( osmium , lead ,uranium) Dehydration : washing with increasing Eathanol concentration

5. Instrumentation of Transmission electron microscopy (TEM)

6. Title and Content Layout with Chart

7. Electron gun The electron gun produces a beam of electrons whose kinetic energy is high enough to allow them to pass through thin area of the TEM specimen. The Gun consists off a electron accelerating region. There are several types of electrons source, each operating on a different physical principle are 1: Tungsten cathode 2: Lanthanum hexaboride (LaB6)

8. Tungsten Cathode Lanthanum hexaboride (LaB6)

9. Condenser lens The wehnelt focuses the beam to a crossover which is accelerated down the column 1: First condenser lens 2: Second condenser lens Condenser Aperture A condenser aperture is a thin disk or strip of metal with a small circular through hole It is used to restrict the electron beams and filter out unwanted scattered electrons before image formation

10. Specimen holder and stages

11. Objective lens The objective lens is used primarily to focus and initially magnify the image. The specimen stage is inserted into the objective lens for imaging purpose the objective lens forms an inverted initial image, which is subsequently magnified. Objective Aperture In the back focal plane of the objective lens a diffraction pattern is first formed. The objective aperture can be inserted here.

12. Sample The beam from the condenser aperture strikes the sample and the electron sample interaction takes place in three different ways 1: One is unscattered electrons (transmitted beams) 2: Elastically scattered electron (diffracted beams) and inelastically scattered electrons

13. Is Diffraction Occur in TEM Yes, it helps to determine the 1: Specimen thickness 2: Crystal Structure 3: Crystal Symmetry

14. Phosphor and fluorescent screen Image modes 1: Bright field microscopy 2: Dark field microscopy 1: Bright field microscopy Separating out electron that are scattered i.e those who have going through the sample Dark and Bright fields for area with high and low degree of electron absorption respectively (Mass thickness contract Dark and Bright fields for area with high and low degree of electron absorption respectively (Diffraction contract)

15. Phosphor and fluorescent screen 2: Dark field microscopy Separating out the electron that have been scattered in a particular direction Light field for area in which electrons have been scattered I the direction chosen (Diffraction contrast) Greater chance of spreading to area with high mass and thickness (Mass thickness contrast)

16. Image recording system The image becomes visible when the electron beam hits a fluorescent screen at the base of the machine The image can be viewed directly through binoculars at the side or on a TV monitor attached to an image

17. How it’s work

18. TEM Image

19. Principal TEM is a complex and sophisticated but the basic principal behind its operation can be readily understood A heated tungsten filament in the electron gun generates a beam of electron that is then focused on the specimen by the condenser Since electron cannot pass through a glass lens , magnetic lenses are used to focus the beam The column containing the lenses and specimen must be under high vaccum to obtain a clear image because electrons are deflected by collision with air molecule

20. The Specimen scatters electron passing through it, and the beam is focused by magnetic lenses to form an enlarged, visible image of the specimen on a fluorescent screen A denser redion in the specimen scatters more electron and therefore appears darker in the image In contrast , electron – Transparent regions are brighter The screen can also be moved aside and the image captured on photographic film as a permanent record

21. How it Works Electron beams are produced from the electron sources Electron beams fall on the sample through the condenser lens Some electrons are transmitted from the sample , the transmitted electrons pass through the objective lens and reach the objective apertaure Then passing through the objective aperture, these electrons fall on the screen through the intermediate lens

22. Here the image develops on the basis of how many electrons have been transmitted . We can see the image on the computer screen We get the image on the basis of how many electrons are scattered here In the sample , the energy of the electron crossing from the electron beams nucleus in the molecule is nt must lost and there is less scatter The electrons of the electron beam which cross through the existing electrons, their energy decreases , they becomes more scattered

23. If the electron are more scatter then the image will appear dark from there The image will appear brighter from where the electrons are less scattered

24. Application TEM provide topographical , morphological , compositional and crystalline information TEM is used to study a sample at the molecular level , to do structure analysis and texture analysis Cancer research : studies of tumor cell ultrastructure

25. Advantage TEM offer very powerful magnification and resolution TEM provide information on element and compound structure Image and high quality and detailed

26. Disadvantages TEM are large and very expensive Laborious sample Preparation Operation and analysis requires special training TEM require special housing and maintenance Image are black and white (2D)