Structures
Nanotechnology has yielded a number of unique structures
that are not found anywhere in nature. Most
demonstrate an essential quality of quantum mechanics known as quantum
confinement. The idea behind
confinement is all about keeping electrons trapped in a small area. The sizes we're talking about here for
confinement have to be less than 30 nm for effective confinement. Quantum confinement comes in several
flavors. 2-D confinement is only
restricted in one dimension, and the result is a quantum well (or plane). These are what most lasers are currently
built from. 1-D confinement occurs in
nanowires. 0-D confinement is found
only in the quantum dot.
You're probably wondering why confinement is so
important. For one thing, it leads to
new electronic properties that are not present in today's semiconductor
devices. Consider the quantum dot. The typical quantum dot is anywhere between
3-60 nm in diameter. That's still 30 to
600 times the size of a typical atom. A
quantum dot exhibits 0-D confinement, meaning that electrons are confined in
all three dimensions. The only things
in nature that have 0-D confinement are atoms.
So a quantum dot can be loosely described as an 'artificial atom'. This is vitally important because we can't
readily experiment on regular atoms.
They're too small and too difficult to isolate in an experiment. Quantum dots, on the other hand, are large
enough to be manipulated by magnetic fields and can even be moved around with
an STM or AFM. We can deduce many
important atomistic characteristics from a quantum dot that would otherwise be
impossible to research in an atom.
Confinement also increases the efficiency of today's
electronics. The laser is based on a
2-D confinement layer that is usually created with some form of epitaxy like
Molecular Beam Epitaxy or Chemical Vapor Deposition. The bulk of modern lasers created with this method are highly
functional, but ultimately inefficient in terms of energy consumption and heat
dissipation. Moving to 1-D confinement
in wires or 0-D confinement in quantum dots allows for higher efficiencies and
brighter lasers. Quantum dot lasers are
currently the best lasers available though their fabrication is still being
worked out.
All of these solid nanostructures are very important to
nanotechnology research. There are
several other structures that are also academically interesting. Nanotubes and Buckyballs are a class of
materials that are hollow. They are all
based on carbon forms that are wrapped to form a shell. The carbon nanotube, for instance, has drawn
much attention as one of the principal nanostructures that exhibit some great
potential in nano-electro-mechanical-systems (NEMS).
In the following sections we shall discuss the many
structures currently under investigation by researchers around the world. After we've finished discussing these
structures, we will move on to their numerous applications in industry and
consumer goods.
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