Nanofabrication Technologies


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Nanofabrication Technologies

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Nanofabrication Technologies

  1. 1. Nanofabrication Technologies<br />
  2. 2. Nanotechnology<br /><ul><li>Fabrication and application of entities whose feature sizes are in the range from about 1 nm to 100 nm
  3. 3. 1 nm = 10-3 m = 10-6 mm = 10-9 m
  4. 4. Entities include structures, films, coatings, dots, lines, tubes, and systems
  5. 5. Nanoscience – the field of scientific study that is concerned with objects in the 1 to 100 nm range
  6. 6. Nanoscale – refers to dimensions within this range and slightly below</li></li></ul><li>Buckyballs (Fullerines)<br /><ul><li>Carbon molecules containing exactly 60 atoms (C60) and shaped like a soccer ball
  7. 7. Originally named buckministerfullerene, after R. Buckminister Fuller, designer of the geodesic dome (shortened to fullerene)
  8. 8. Can be bonded together to form crystals whose lattice structure is face-centered cubic</li></li></ul><li>Buckyballs<br /><ul><li>Structure of C60 molecule
  9. 9. 12 pentagonal faces
  10. 10. 20 hexagonal faces</li></li></ul><li>Carbon Nanotubes<br /><ul><li>Another nanostructure of interest, consisting of carbon atoms bonded together in the shape of a long tube
  11. 11. Depending on structure and diameter, can have conducting or semiconducting properties
  12. 12. Conductivity superior to copper due to fewer defects that increase electrical resistance
  13. 13. Thus, high currents do not increase temperature as in metals
  14. 14. Elastic modulus and tensile strength of carbon nanotubes much greater than steel</li></li></ul><li>Carbon Nanotubes<br />armchair <br />(b) zigzag<br />
  15. 15. Production of Carbon Nanotubes<br /><ul><li>Laser evaporation method
  16. 16. Carbon arc techniques
  17. 17. Chemical vapor deposition</li></li></ul><li>Laser Evaporation Method<br /><ul><li>Starting material is graphite with traces of Co and Ni that act as nucleation sites in formation of nanotubes
  18. 18. Graphite workpiece is placed in quartz tube filled with argon and heated to 1200°C
  19. 19. A pulsed laser beam is focused on surface, causing carbon atoms to evaporate from the bulk graphite
  20. 20. Argon moves carbon atoms to cool copper surface, where they condense, forming nanotubes with diameters 10 to 20 nm and lengths ~ 100 m</li></li></ul><li>Carbon Arc Technique<br /><ul><li>Uses two carbon electrodes that are separated by 1 mm and located in a partial vacuum
  21. 21. 25 V is applied across the electrodes, causing carbon atoms to be ejected from positive electrode and carried to negative electrode where they form nanotubes
  22. 22. If no catalyst – multi-walled nanotubes form
  23. 23. If cobalt used as catalyst, single-walled nanotubes with diameters 1 to 5 nm and lengths ~ 1 m</li></li></ul><li>Chemical Vapor Deposition<br /><ul><li>Starting material is hydrocarbon gas such as methane (CH4)
  24. 24. Gas is heated to 1100°C, causing it to decompose and release carbon atoms
  25. 25. Atoms condense on cool substrate to form nanotubes
  26. 26. Substrate surface may contain metallic traces that act as nucleation sites for nanotubes
  27. 27. CVD process can be operated continuously, making it attractive for mass production</li></li></ul><li>Dip-Pen Lithography<br /><ul><li>Tip of an atomic force microscope is used to deposit molecules through the water meniscus that forms naturally between the tip and the substrate</li></li></ul><li>Micro-Imprint Lithography<br /><ul><li>Flat mold positioned above resist, (2) mold is pressed into resist surface, (3) mold is lifted, (4) remaining resist removed by etching to expose substrate surface</li>