So, this demonstration is meant to
illustrate how current flows in a wire.
I have here a table, which represents a
wire, and remember that
a wire is a piece of metal, which is not
perfectly crystalline, it
has defects, and when electrons run into
those defects, that impedes their
flow, and that gives rise to what we call
resistance in the wire.
So, these golf balls, symbolize my
electrons.
And these cups, symbolize defects.
And when I release
a flow of electrons, you're going to see
that
some of them will flow unimpeded, not
running
into anything, but some of them will run
into defects, and their flow will be
impeded.
So let's see how that works.
[SOUND]
Now, another thing to remember, is that
the defects that form
in a wire, are located randomly with a
certain average density.
So as the wire becomes smaller and
smaller, eventually you might reach a
point where,
it's so small that the probability of
finding
a defect inside that wire, is very low.
And, so that's the next thing we want to
try.
So, now instead of having a big wire, we
have a small wire.
Maybe a nanowire.
And, because the wire is small, the
probability of
finding defects inside the wire is lower
and so you
have a smaller number of defects, and
therefore the flow
of current is impeded less by collisions
with the defects.
[NOISE]
And
most of my electrons make it to the end of
the wire without running into anything.
So now, we've made our wire even smaller.
Now we can consider it to be a one
dimensional conductor.
And in this case defects become a real
problem, because if you do have a
defect in the middle of a one
dimensional wire, then every electron
ecnounters that defect.
[SOUND]
Even, one defect, in a one-dimensional
wire, can make a big difference.
So we've seen that defects in the crystal
structure of
a metal can play a critical role in
determining the
resistance of a wire, as you go from a
large
wire, to a nanowire, and down even to a
one-dimensional wire.
This turns out to be one of the crucial
challenges that
one faces when one tries to
construct electrical circuits using
nanoscale components.