Super saturation of iron interstices by carbon
In this step a carbon based gas is pushed into a chemical vapor deposition
machine supersaturating the iron interstices and creating the carbon nanotubes. What
this means is that the small spaces between the atoms of iron, or the interstices, are
filled with a gas containing carbon. The most commonly used gases are acetylene (HC2
H), ethylene (C2 H 4), ethanol (C2H5OH), or methanol (CH3OH). This process takes
place in a furnace that is vacuumed of other gases and sealed of outside air; in this
case it is a nano-chemical vapor deposition machine. The metal catalyst (in this case,
iron), was already deposited as a gas onto the silicon wafer and solidified. We know
that the iron is then heated to a minimum of 800 degrees Celsius. However, iron’s
melting point is considerably higher, at 1,538 degrees Celsius. While the iron will not
melt, the iron will bead and form these interstices. We believe or think that the iron acts
as a seed for the carbon nanotubes. The carbon acts like water in the sense that it
makes the carbon nanotubes grow.
To give you a visual(picture below, of jar) the marbles are the iron (which were
heated not melted into spherical shapes or beads).the carbon based gas acts as water
and begins to fill the spaces in between the marbles(iron interstices which is the space
in between the iron atoms). Slowly the jar becomes full and begins to overflow. The
carbon forms fullerenes or spherical structured molecules, which in turn form the carbon
nanotube “tower” structures. What is unknown is the actual mechanism that makes the
carbon nanotubes grow. The most common belief is that the force of the carbon gas
being pushed out of those interstices forms these tower like structures.
Carbon nanotube growth studying the effect of free energy on carbon nanotube growth using
materials studio from accelrys AZoNanotechnology Article
December 3, 2009. Leslie Hawes. February 28, 2009. Secret Recipes.
December 3, 2009.