A group of engineers and
researchers working together from IBM, Purdue University, and the
University of California at Los Angles has learned to create
nanowires coated with materials that make for efficient
transistors. The nanowires have very sharply defined layers at the
atomic level that allow the wires to be efficient transistors.
Stach, associate professor of materials Engineering from Purdue said,
"Having sharply defined layers of materials enables you to
improve and control the flow of electrons and to switch this flow on
The team of researchers says that
electronic devices are often constructed of heterostructures. The
term heterostructures means that the structure contains sharply
defined layers of different semiconducting materials like silicon and
germanium. According to the researchers, the challenge in the past
has been the capability of producing nanowires with the requisite
The team has detailed its findings in a
paper published in the November 27 edition of the journal Science.
The transistors that the team have developed are not made on flat
pieces of silicon. These nanowires are grown vertically making them
have a much smaller footprint, which in turn allows for many more of
the nanowires to be placed on the same piece of silicon.
Stach said, "But first we need to
learn how to manufacture nanowires to exacting standards before
industry can start using them to produce transistors."
The researchers used a transmission
electron microscope to view the nanowire formation. The nanowires
were formed by heating tiny particles of a gold-aluminum alloy in a
vacuum chamber. After the alloy was melted the researchers introduced
silicon gas and the alloy bead absorbed the gas becoming
supersaturated with silicon. This caused a silicon wire to grow from
the alloy bead producing a silicon wire that was topped with a
mushroom-like gold-aluminum alloy bead.
At that point, the researchers reduced
the temperature of the chamber enough to allow the alloy bead at the
top of the wire to solidify, thereby allowing germanium to be
deposited on the silicon precisely creating the required
heterostructure needed to create a transistor. The heterostructure
allows the formation of a germanium gate in each transistor allowing
devices to switch on and off.
"The cycle could be repeated,
switching the gases from germanium to silicon as desired to make
specific types of heterostructures," Stach said.