nanofabrication technologies
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Nanofabrication TechnologiesTRANSCRIPT
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
(a)armchair
(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