1. Electron Microscope

2. Comparison b/w light and electron microscopes LIGHT MICROSCOPE ELECTRON MICROSCOPE Magnification can be done upto 2000 times Resolving power is less Photons are involved Magnificationcan be done upto 2 million times Have much greater resolving power than ordinary microscope Electrons are involved

3. Scale 3

4. Reason for greater resolution and magnification of electron microscope Wavelength of an electron[de Broglie] is very much smaller than that of a light photon Wavelength of an electron = λ=h/(√2mE) Wavelength of a light photon = λ=h/E

6. Year-1933

8. Construction of EM [TEM]

9. THE ELECTRON GUN

10. WORKING OF AN ELECTRON MICROSCOPE

11. Types of ELECTRON MICROSCOPE

12. TRANSMISSION ELECTRON MICROSCOPE

15. Construction and working

16. TEM ELECTRON GUN ELECTROMAGNETIC LENSES VACUUM PUMPS OPENING TO INSERT SAMPLES OPERATION PANEL DISPLAY SCREEN WATER SUPPLY TO COOL THE INSTRUMENT

17. ELECTRON GUN The electron gun produces a stream of monochromatic electrons of energy 100-400keV . The extraction of electrons is of two types 1. Thermionic emission using thermal energy 2. Field emission by applying very large electric field 1010 A/m FE gun is more expensive and must be used in high vacuum conditions.

18. FIELD EMISSION GUN

19. The beam of electrons is focused using condenser lenses [1&2] The beam is restricted by the condensor aperture Then it strikes the specimen and transmitted The transmitted portion is focused by Objective Lens into an image Intermediate and projector lenses enlarge the image Image is formed on phosphor screen Darker area – few electrons – thick region Lighter area – more electrons – thin region.

20. Transmission electron microscopy

22. very high resolution

23. Resolving power is

24. Magnification is 1,000,000 times greater than the size of the object

27. To get 2-D Image of biological cells , virus , bacteria etc.

28. In fields such as thin film technology , metallurgy , microbiology etc.

31. It captures the images of the specimen surface by scanning it with a high-energy beam of electrons , in a scan pattern

32. produces a 3-dimensional image of specimen’s surface features24

34. SEM electron gun electromagnetic lenses vacuum pumps opening to insert specimen operation panel screen for display cryo – unit for cryosem electronic instruments

36. If a non conductive material has to be viewed , then it has to be coated by a thin layer of electrically conductive material

38. SPUTTERING

39. WORKING SEM produces signals in the form of secondary electrons , backscattered electrons, characteristic x-rays , light , specimen current, and transmitted electrons These signals are formed by the interaction of the electron beam with the surface of the specimen and require specialized detectors for their detection Depth of the specimen can be expressed in the image Back scattering of electrons help to detect the distribution of elements in the specimen

40. CHARACTERISTIC X-RAY SIGNAL 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 Help to identify the composition of elements in sample

41. Scanning Electron Microscope

43. Image can be directly viewed

44. 3-Dimensional image can be obtained

45. has large depth of focus

47. preparation of sample is difficult and tedious

49. wide application in medical , science and engineering fields

50. To find the structural composition of paper pulps, ceramic materials , polymers etc.

52. SEM AND TEM PHOTOS SEM TEM

53. Comparison of images SEM of the compound eye of a fly! TEM of bacteria

54. Some more images obtained using SEM SEM of Yersiniapestis – which causes plague SEM image of Streptococcus pyogenes , which causes scarlet fever

55. EM Image of the chloroplast of spinach

56. EM Image of RBC

57. SEM Image of a mesh

58. RBC OF MAN

59. NEURON CELL

60. MOSQUITO

61. CULTURED CELLS OF HUMAN BEING

62. HUMAN CELLS

63. HEAD OF A BLACK ANT

64. Websites for further info: www.nobelprize.org www.wikipedia.com www.pbrc.hawaii.edu/microangela www.mos.org/sln/SEM/ www.britannica.com/EBchecked/topic-art/183561/110970/Scanning-electron-microscope

65. Presentation done by… SHANTHA KUMAR . T EEE RMD ENGG COLLEGE

66. THANK YOU!