Electron Microscope Shanthakumar

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Electron Microscope Shanthakumar

  1. 1. Electron Microscope<br />
  2. 2. Comparison b/w light and electron microscopes<br />LIGHT MICROSCOPE<br />ELECTRON MICROSCOPE<br />Magnification can be done upto 2000 times<br />Resolving power is less<br />Photons are involved<br />Magnificationcan be done upto 2 million times<br />Have much greater resolving power than ordinary microscope<br />Electrons are involved<br />
  3. 3. Scale<br />3<br />
  4. 4. Reason for greater resolution and magnification of electron microscope<br />Wavelength of an electron[de Broglie] is very much smaller than that of a light photon<br />Wavelength of an electron = λ=h/(√2mE)<br />Wavelength of a light photon = λ=h/E<br />
  5. 5. First Electron Microscope<br /><ul><li>Invented by Ernst Ruska
  6. 6. Year-1933
  7. 7. He was awarded the Nobel Prize for physics for his invention in 1986</li></li></ul><li>Construction Of An Electron Microscope<br />
  8. 8. Construction of EM [TEM]<br />
  9. 9. THE ELECTRON GUN<br />
  10. 10. WORKING OF AN ELECTRON MICROSCOPE<br />
  11. 11. Types of ELECTRON MICROSCOPE<br />
  12. 12. TRANSMISSION ELECTRON MICROSCOPE<br />
  13. 13. TEM<br /><ul><li>Developed by ERNST RUSKA and MAX KNOLL in 1931 in germany
  14. 14. It was the first type of electron microscope to be invented</li></li></ul><li>When a beam of electrons is passed through a specimen , a part of it is transmitted and this part when projected on fluorescent screen , its image can be seen by the observer<br />PRINCIPLE<br />
  15. 15. Construction and working<br />
  16. 16. TEM<br />ELECTRON GUN<br />ELECTROMAGNETIC LENSES<br />VACUUM PUMPS<br />OPENING TO INSERT SAMPLES<br />OPERATION PANEL<br />DISPLAY SCREEN <br />WATER SUPPLY TO COOL THE INSTRUMENT<br />
  17. 17. ELECTRON GUN<br /> The electron gun produces a stream of monochromatic electrons of energy 100-400keV . <br /> The extraction of electrons is of two types<br /> 1. Thermionic emission using thermal energy<br /> 2. Field emission by applying very large electric field 1010 A/m<br /> FE gun is more expensive and must be used in high vacuum conditions.<br />
  18. 18. FIELD EMISSION GUN<br />
  19. 19. The beam of electrons is focused using condenser lenses [1&2]<br /> The beam is restricted by the condensor aperture<br /> Then it strikes the specimen and transmitted<br /> The transmitted portion is focused by Objective Lens into an image<br />Intermediate and projector lenses enlarge the image<br /> Image is formed on phosphor screen<br /> Darker area – few electrons – thick region<br /> Lighter area – more electrons – thin region.<br />
  20. 20. Transmission electron microscopy<br />
  21. 21. Advantages <br /><ul><li>versatile technique for the characterisation of materials
  22. 22. very high resolution
  23. 23. Resolving power is
  24. 24. Magnification is 1,000,000 times greater than the size of the object
  25. 25. Information about crystal structure and chemical composition can be collected simultaneously</li></li></ul><li>Disadvantages<br />No 3-D image<br />Aberrations due to lenses<br />Absorption of electrons heats up the sample and changes its characteristics<br />Larger current density[j] and hence more current I=jA {A- Illuminated area}<br />Specimen must be thin because due to strong absorption of electrons , the penetration depth is small<br />
  26. 26. APPLICATIONS<br /><ul><li>In nano science , to find the internal structure of nanomaterials
  27. 27. To get 2-D Image of biological cells , virus , bacteria etc.
  28. 28. In fields such as thin film technology , metallurgy , microbiology etc.
  29. 29. In studying the compositions of paints , alloys etc.</li></li></ul><li>Scanning Electron Microscope<br />
  30. 30. The Scanning Electron Microscope<br /><ul><li>uses electrons reflected from the surface of a specimen to create image
  31. 31. It captures the images of the specimen surface by scanning it with a high-energy beam of electrons , in a scan pattern
  32. 32. produces a 3-dimensional image of specimen’s surface features</li></ul>24<br />
  33. 33. PRINCIPLE<br /><ul><li>The electrons interact with the atoms that make up the specimen, producing signals that contain information about its surface topography , composition and other properties such as electrical conductivity</li></li></ul><li>CONSTRUCTIONPARTS of SEM <br />
  34. 34. SEM<br />electron gun<br />electromagnetic lenses<br />vacuum pumps<br />opening to insert specimen<br />operation panel<br />screen for display<br />cryo – unit for cryosem<br />electronic instruments<br />
  35. 35. PREPARATION OF SAMPLES<br /><ul><li>Samples must be electrically conductive
  36. 36. If a non conductive material has to be viewed , then it has to be coated by a thin layer of electrically conductive material
  37. 37. This coating is done using a sputter coater</li></li></ul><li>GOLD COATED INSECT WHICH IS TO BE VIEWED THROUGH SEM<br />
  38. 38. SPUTTERING<br />
  39. 39. WORKING<br />SEM produces signals in the form of secondary electrons , backscattered electrons, characteristic x-rays , light , specimen current, and transmitted electrons<br />These signals are formed by the interaction of the electron beam with the surface of the specimen and require specialized detectors for their detection<br />Depth of the specimen can be expressed in the image<br />Back scattering of electrons help to detect the distribution of elements in the specimen<br />
  40. 40. CHARACTERISTIC X-RAY SIGNAL<br />Characteristic x-ray signals are formed when the electron beam removes an inner shell electron of the sample causing a high energy electron to fill the space and release energy<br />Help to identify the composition of elements in sample<br />
  41. 41. Scanning Electron Microscope<br />
  42. 42. ADVANTAGES OF SEM<br /><ul><li>used to examine specimens of large thickness
  43. 43. Image can be directly viewed
  44. 44. 3-Dimensional image can be obtained
  45. 45. has large depth of focus
  46. 46. very high magnification from x25 to x250,000</li></li></ul><li>DISADVATAGES OF SEM<br /><ul><li>The Resolution of image is poor
  47. 47. preparation of sample is difficult and tedious
  48. 48. some samples can loose their structural property due to their interaction with the electrons</li></li></ul><li>APPLICATIONS<br /><ul><li> Specimens of large thickness can be examined
  49. 49. wide application in medical , science and engineering fields
  50. 50. To find the structural composition of paper pulps, ceramic materials , polymers etc.
  51. 51. Used to get 3-D image of biological cells, DNA , Bacteria etc.</li></li></ul><li>Comparison<br />SEM<br />TEM<br />
  52. 52. SEM AND TEM PHOTOS<br />SEM<br />TEM<br />
  53. 53. Comparison of images<br />SEM of the compound eye of a fly!<br />TEM of bacteria<br />
  54. 54. Some more images obtained using SEM<br />SEM of Yersiniapestis – which causes plague<br />SEM image of Streptococcus pyogenes , which causes scarlet fever<br />
  55. 55. EM Image of the chloroplast of spinach<br />
  56. 56. EM Image of RBC<br />
  57. 57. SEM Image of a mesh<br />
  58. 58. RBC OF MAN<br />
  59. 59. NEURON CELL<br />
  60. 60. MOSQUITO<br />
  61. 61. CULTURED CELLS OF HUMAN BEING<br />
  62. 62. HUMAN CELLS<br />
  63. 63. HEAD OF A BLACK ANT<br />
  64. 64. Websites for further info:<br />www.nobelprize.org<br />www.wikipedia.com<br />www.pbrc.hawaii.edu/microangela <br />www.mos.org/sln/SEM/<br />www.britannica.com/EBchecked/topic-art/183561/110970/Scanning-electron-microscope<br />
  65. 65. Presentation done by…<br />SHANTHA KUMAR . T<br />EEE<br />RMD ENGG COLLEGE<br />
  66. 66. THANK YOU!<br />

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