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