Pollen photos using a Scanning Electron Microscope
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The document compares the scanning electron microscope (SEM) to the light microscope. It states that the SEM can achieve much higher magnifications than the light microscope, up to 500,000x compared to 1000-1500x, because electrons have a much shorter wavelength than visible light. This allows the SEM to achieve much higher resolving power and see finer detail, around 4nm, versus around 200nm for the light microscope. It also notes some key differences in their operation, such as the SEM using electrons rather than visible light and requiring a vacuum rather than air-filled interior.
Pollen photos using a Scanning Electron Microscope
- 1. Scanning Electron Microscope Pollen Chris Cardew 28th February 2016
- 2. Light Microscope • A modern light microscope - 1000x . • The resolving power of the microscope limited by the wavelength of the light used for illumination. • Using light with a shorter wavelength--a small improvement. • Using oil --- small improvement, but all together only brought the resolving power of the microscope to just under 100 nm. Dr Ganga H
- 3. Dr Ganga H
- 4. Resolution of a microscope • Wavelength of the illumination source ( λ ) • The numerical aperture of the lens (N.A.) Limit of resolution = 0.61 λ/N.A. • The maximum value of N.A. for a light microscope is approx. 1.4. therefore even the short blue light ( λ = 436 nm) of the visible spectrum will yield a resolution of only 190 nm. • The wavelength of an electron beam is about 100,000 times less than that of visible light and hence the resolution of an electron microscope is far superior to that of the light microscope. • NA is the light gathering ability and resolution of the acceptance cone of an objective Dr Ganga H
- 5. Dr Ganga H
- 6. THE LIGHT MICROSCOPE v THE ELECTRON MICROSCOPE VacuumAir-filledInterior MagnetsGlassLenses High voltage (50kV) tungsten filament Tungsten or quartz halogen lamp Radiation source X 500,000x1000 – x1500 Maximum magnification 0.14nm Fine detail app. 200nm or 0.2micron Maximum resolving power Electrons app. 4nm Visible light 390nm (red) – 760nm Electromagnetic spectrum used ELECTRON MICROSCOPELIGHT MICROSCOPEFEATURE © 2007 Paul Billiet ODWS Focus Lens is movable Rigidly fixed, adjust lens currents
- 7. THE LIGHT MICROSCOPE v THE ELECTRON MICROSCOPE Copper gridGlass slideSupport Heavy metalsWater soluble dyesStains Ultramicrotome Slices - 50nm Parts of cells visible Microtome slices - 20 000nm Whole cells visible Sectioning ResinWaxEmbedding Glutaraldehyde,OsO4formaldehydeFixation ELECTRON MICROSCOPE LIGHT MICROSCOPEFEATURE © 2007 Paul Billiet ODWS Focussing screen Human eye (retina), photographic film Fluorescent screen, photographic film
- 8. Scanning Electron Microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons ‘The German scientists Max Knoll and Ernst Ruska realized that, since the wavelength (the distance between successive peaks or troughs of any wave) associated with electrons was much shorter than the wavelength of visible light, a microscope based on electron imaging should be able to pick out much finer detail than an optical microscope. This is because any tiny object or detail that has dimensions smaller than the wave falling on it will not influence or affect the wave’
- 14. Field Thistle pollen x400 using a light microscope
- 15. Field Thistle 2500 times Intine
- 16. Field Thistle 2500 x 42.4um
- 17. Field Thistle x 2000 Intine
- 18. Field Thistle x 2000
- 19. Field Thistle 6000 x
- 20. Field Thistle x 8000
- 21. Field Thistle x 2500
- 22. Field Thistle x 2500
- 23. Field Thistle x 3000
- 24. Field Thistle x 3000
- 25. Field Thistle x 2500
- 26. Field Thistle x 2500
- 27. Field Thistle x 2000
- 28. Field Thistle x 2000
- 29. Field Thistle x 3000
- 30. Field Thistle x 2000
- 31. Field Thistle x 3000
- 39. Hogweed x 4000
- 40. Hogweed x 4000