Graphene appears to have many of the properties needed to usher in the next
generation of electronic devices. The next step in building those devices, however,
requires creating junctions that connect graphene to the external world through
at least two metal wires. A two-terminal junction is a graphene ribbon with two
metal contacts. A University of Arkansas researcher and his colleagues have
developed a better understanding of how these graphene-metal interfaces affect
the movement of electrons through two-terminal junctions.
Salvador Barraza-Lopez, assistant professor of physics, Markus Kindermann of
Georgia Institute of Technology, and M.Y. Chou of Georgia Tech and the Academia
Sinica in Taiepi, Taiwan, report their findings in NanoLetters.
“If you want to use graphene for devices, you want to understand what will
happen with metal contacts,” Barraza-Lopez says.
Current theories about graphene devices assume that the contacts that move
electricity from one point to another will also be composed of doped graphene,
meaning that the contacts have a large amount of electronic charge, as actual
metals would have. But contacts in real devices are made of transition metals,
and those metal contacts will form bonds with graphene.
“When you form covalent bonds, you destroy the unique electronic properties of
graphene,” Barraza-Lopez says. “So we thought it was important to calculate the
transport of electrons going beyond the assumption that the contacts themselves
are (doped) graphene.”
He and his colleagues set out to look at how electrons can move through
graphene junctions with titanium, which is used by many experimental teams as a
contact with graphene: They considered the material properties of actual
junctions, and contrasted their findings with more basic models already
available. Their calculations were done using the principles of quantum
mechanics and state-of-the-art computational facilities.
Within quantum mechanics, the electrons at these graphene-metal junctions
behave much like a light beam does when it is shone on a crystal—some of the
light scatters and some of it goes through. For graphene junctions the
electronic transparency of the material indicates how many of the electrons on
one contact make it through the other metal contact. In this work, the
researchers have provided the most accurate calculations of the electronic
transparency of realistic graphene-metal junctions to date.
“Our results shed light on the complex behavior of graphene junctions … and
pave the way for realistic design of potential electronic devices,” the
Source: University of Arkansas