a really, really, really, really small world after all
from microstructures to nanostructures allows materials scientists
to take technology to the next level.
Parthasarathy used to consider the big picture, but now he attends
to the small details. As an astrophysics major at the University
of California at Berkeley he became more interested in the tiny
electronics of the telescope's inner space than the swirling clouds
of outer space. Switching his focus from radio astronomy to semiconductors,
the Ph.D. candidate in physics has moved to the other end of the
scale-he measures in nanometers rather than parsecs.
will graduate this summer after five years at Chicago-works with
nanostructures, objects roughly 1 billionth of a meter in diameter,
or several hundred times smaller than a human blood cell. Current
technology operates on the microscale, measuring items about 1
millionth of a meter across. By examining the behavior of the
much smaller nanostructures, materials scientists like Parthasarathy
hope to pave the way for smaller and faster electronics.
devices on the nanoscale, however, presents problems of quantum
mechanics not encountered on the microscale. "On the nanoscale
you can only fit one extra electron on a device, as opposed to
billions on a piece of wire," explains Parthasarathy. "Two
electrons a micrometer away from each other will be fine, but
put them a nanometer away and they will strongly repel each other.
Only one will be able to occupy the space." Nanometric particles
also create new physical phenomena-such as emitting differently
colored lights-when squeezed into areas smaller than their wavelength.
"It's not just new technology," he says. "It's
dissertation work involves placing organically encased, six-nanometer
diameter gold spheres into a slippery liquid on a chip (a process
developed by lab partner Xiao-Min Lin, a postdoctoral researcher
in physics). The slick surface helps the spheres-or nanocrystals-self-assemble
into a hexagonal pack. When an electric charge is sent across
the pack its electrons repel each other because of their close
proximity, inhibiting the charge's progression across the array.
"If you send a current through a block of metal there is
just a river of charge flowing through the material," Parthasarathy
explains. "But because these crystals are so small, only
one electron fits on each. So you get a flow of current that is
more like a traffic jam, with spurts of movement here and there."
Instead of a free-flowing river, the charge acts like water being
forced through a sponge, following different paths to get to the
other side. Parthasarathy and Lin have been able to characterize
what these pokey flows look like, with organized as well as with
messy arrays, to tell whether an array's orderliness affects how
the paths branch.
all materials science, nanoscience advances in baby steps-some
of Parthasarathy's experiments have no clear applications beyond
forcing nanocrystals into situations just to see how they will
react. While years away from the wonders of Star Trek,
Parthasarathy hopes that it won't be long before physicists can
manipulate nanostructures to create "artificial atoms."
By assembling these crystals in different patterns to create new
solids-the way nature assembles carbon atoms one way to make diamonds
and another to make graphite-materials could be designed with
specific electronic properties like magnetism or superconductivity.
But before that can happen, physicists need to see how nanostructures
can be manipulated under the microscope, all the while keeping
sight of the big picture.