Computer Modeling
The unsung champions
in nanotechnology are the many theorists, mathematicians, physicists, and
computer modelers who strive endlessly to gain insight into the nanoscale
world. For every experiment that
results in recorded empirical data, it's vitally important for scientists and
engineers to see how that data fits in with their theory and models. If there is a serious deviation between the
two, it could mean there are problems with the experiment, the model, or both!
Theorists don't have
it easy. They work in an abstract world
of numbers and graphs. The inherent
challenge of theory in the nanoscale is that scientists must work in an
intermediate world between quantum theory (that governs atoms) and bulk theory
(which governs macroscopic materials).
Most nanoscale structures and devices are at least 3-20 nm across. In this range, it isn't appropriate to model
a semiconductor nanowire, for instance, as a cylindrical quantum well of
infinite length. That would be the bulk
model. The thing is, a nanowire that is
only 10 nm across is only 100 atoms in diameter. At this scale, you can't use bulk values to extract the wire's
electronic properties. Instead, you'll
need to take into account the fact that in the nanoscale, atoms (and their
lattice positions) are extremely important.
To make things
worse, molecular theory is not a complete science. In fact, it is impossible to fully solve a two-hydrogen (the
standard H
2 gas molecule) system without having to make serious
sacrifices in the model you choose to use.
So taking a fully atomistic approach won't work either.
In the end,
successful theories have mixed the two worlds of atoms and bulk systems of
atoms in order to elucidate the nature of many nano structures like quantum
dots and wires. These calculations are
very extensive. If you did them by hand it would take months to complete. Luckily, simple calculations with results
within a few percent-error of more complex calculations only require about 30
minutes to an hour. Serious
calculations can require several hours at once.
These results are
very important because our current synthesis methods are not that precise. We often end up with a spread of diameters
when making nanowires, so it's extremely difficult to analyze the empirical results. This is why theory is important. It opens windows of knowledge that were
previously closed to us. Though often
the theory and experimentation don't match up completely, we can't do one
without having the other. It's a
dynamic balance that continually seeks to re-adjust itself as we progress with
our scientific endeavors.
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