Your news round-up from
the big world of the incredibly small. February 2001 edition
While we've been resting
up, the small world has been getting bigger. Some of the work is even practical,
which may come as a surprise; researchers at the University of Illinois
have made in interesting plastic that fixes itself. If you've used two-part
epoxy glue, you'll understand how it works. The plastic itself is mixed
with something like epoxy hardener. Inside the plastic are billions of
little bubbles, each one containing a small quantity of runny resin glue.
B
offins
call this "microencapsulation", but the interesting part happens when things
get de-microencapsulated. If the plastic is stressed out, say by that big
snapper you caught that nearly bent the rod right round, cracks appear
in the plastic. If this is your fishing rod, you'd normally have a broken
rod and a good tale to tell at the fishing club. But with the new plastics,
the micro-cracks that form as the plastic bends savagely break into the
microscopic capsules and the runny resin squirts out. It comes out of the
tiniest break in the bubble wall and is sucked along the cracks like kerosene
along a wick. As it goes along the crack (as shown on the right), it hardens
off because of the hardener in the plastic - and you get one self-gluing,
unbroken plasticy thing. Your rod lives another day and the snapper goes
on the barbie.
Of course, this wasn't invented with the aim of helping fishermen. Self-healing
plastics like this will help improve the safety of any machine which has
plastic parts in a hard-to-get-at place, from aircraft to circuit boards
to artificial heart valves. Current limits are placed by being able to
make the capsule walls strong enough to survive manufacturing the plastic
item. But as techniques of making the capsules smaller than the current
0.1 mm improve, the strength of the plastic will increase further. At last,
a technology that's all it's cracked up to be.
Penn Rules The Lines
While some researchers try to figure out how to create really tiny electrical
devices, others take on the practical task of figuring out how to make
wires small enough to connect them up to silicon chips with. Penn
State University has
figured
a way of not only making very fine wires, but of spacing them out regularly
while they're at it. "We have known how to make smaller and smaller structures
by using techniques that have been developed for the fabrication of computer
chips, and we also have known how to make molecules bigger and bigger,"
says Paul Weiss, associate professor of chemistry at Penn State. "But that
intermediate region between the two approaches has been essentially inaccessible,
and our technique of using 'molecular rulers' represents a step toward
bridging that gap."
The
way they make these rulers a bit tricky to get your head around, so I've
made this picture on the left. It starts off with a trick called
"electron
beam lithography" , which is basically etching things with a very fine
beam of electrons. It's not practical to etch thick wires with this trick,
but a strip (1) of the base material can be 'seeded' by it. A layer of
unpleasant organic stuff (2) called mercaptoalkanoic acid grows on the
seed, spreading out like an ANZAC biscuit on a baking sheet. They know
how fast it spreads, so they know how much of the base it has covered.
Finally, gold (3) is used to fill in the gaps, and the gold nanowires are
complete. The bigger the biscuit, the thinner the wires.
The wires in the picture are 15 nanometers wide, or roughly 70,000 to
the millimeter. So that's not a lot of gold. The next trick is to figure
out how to move the other end around and stick it to the right place on
a silicon chip, but they're working on that in other places.
Many-Armed Zyvex
Zyvex,
and independent nanotechnology company, have teamed up with a company called
Standard MEMS to produce a very
simple but very small robotic arm from silicon like silicon chips are made
from. It's not a very versatile item, but the clever thing about this arm
is that it can be used to put together another arm from prefabricated bits.
Of course, someone has to put the first one together with great care and
a really good microscope, but once that is done they have a very fine tool
indeed.
But wait, there's more. So your first arm has assembled another and
you have 2 arms, as is happening in the picture from Zyvex on the right.
These arms can now make another 2, so you get 4. Then they make 8, which
make 16, 32 64, 128 and after 10 goes at this you have more than a thousand.
Want two thousand? Do it one more time. This is called exponential
assembly and will allow the manufacture of very large numbers of small
machines - including better arms - on the same scale as which we now manufacture
silicon chips.
Grow Your Own Slaystation
There's another way to get tiny chips built, and that's to get them to
build themselves. If you get the right parts to join together in the right
way, you can build yourself your own games console, computer, MP3 player
or just about anything else. Researchers at the
University
of Los Angeles have made a chemical which is a small, electrical switch.
Unlike previous attempts at the same thing which need to be frozen so cold
the air freezes on them, theirs works at room temperature. The molecules
of the chemical are made of two interlocked rings, and depending on which
way they get twisted, they turn electricity flowing through them on or
off.
But one of these little switches on its own isn't much good, and so
the researchers have persuaded them to line up side by side, making something
a bit like small-scale chainmail and effectively growing a computer like
kids grow crystals. Their current estimates are that we'll see a computer
built using these things by 2006, as long as they can solve the wiring
up problem by using the nanowires form the first article and the little
assembler arms from the previous article. Computer games could get a heck
of a lot fancier with this technology powering them.
Smallest
Robot Yet
Now this one is just plain cute. It's a little robot which fits quite happily
on top of a 5 cent coin. There it is on the left, in a nice little picture
from it's creator; Sandia Labs. It
runs around on two little tank tracks until things get too warm, then it'll
back off and try a different route. In short, it has just enough brains
to run around without getting burnt. Most of the robot is take up by the
tiny watch batteries. Two miniature motors power the tracks, and the computer
chip that controls it all is mounted on a special glass circuit to save
space. The body of the robot was made by the 3D printing processes described
in the last issue of SmallTalk. Future robots
like this will be handy for police and military surveilance, finding landmines
and exploring the extent of chemical spills. Oh, and they look really cute
crawling around a glass-topped coffee table!
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