Biomedical Engineering Reference
In-Depth Information
FIGURE 1.6
MWNTs with a diameter of 30 nm and length of 12
m have been formed within 2 min
[10]
.
µ
landscape, but also the electronic landscape
[9]
. Here they have positioned 48 iron atoms into a cir-
cular ring in order to “corral” some surface state electrons and force them into “quantum” states of
the circular structure (
Figure 1.5
). The ripples in the ring of atoms are the density distribution of a
particular set of quantum states of the corral. The artists were delighted to discover that they
could predict what goes on in the corral by solving the classic eigenvalue problem in quantum
mechanics—a particle in a hard-wall box.
Probably the most publicized material in recent years has been CNTs. CNTs, long, thin cylin-
ders of carbon, were discovered in 1991 by S. Iijima. These are large macromolecules that are
unique for their size, shape, and remarkable physical properties. They can be thought of as a
sheet of graphite (a hexagonal lattice of carbon) rolled into a cylinder. These intriguing structures
have sparked much excitement in recent years and a large amount of research has been dedicated
to their understanding. Currently, the physical properties are still being discovered and disputed.
What makes it so difficult is that nanotubes have a very broad range of electronic, thermal, and
structural properties that change depending on the different kinds of nanotube (defined by its
diameter, length, and chirality, or twist). To make things more interesting, besides having a single
