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Nanofabrication Technologies

Nanofabrication Technologies



Nanofabrication Technologies

Nanofabrication Technologies



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    Nanofabrication Technologies Nanofabrication Technologies Presentation Transcript

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