(August 4, 2015) Graphene
has been called a wonder material, capable of performing great and unusual
material acrobatics. Boron nitride nanotubes are no slackers in the materials
realm either, and can be engineered for physical and biological applications.
However, on their own, these materials are terrible for use in the electronics
world. As a conductor, graphene lets electrons zip too fast—there’s no
controlling or stopping them—while boron nitride nanotubes are so insulating
that electrons are rebuffed like an overeager dog hitting the patio door.
But together, these two materials make a workable digital
switch, which is the basis for controlling electrons in computers, phones,
medical equipment and other electronics.
Yoke Khin Yap, a professor of physics at Michigan
Technological University, has worked with a research team that created these
digital switches by combining graphene and boron nitride nanotubes. The journal
Scientific Reports recently published their work.
“The question is: How do you fuse these two materials
together?” Yap says. The key is in maximizing their existing chemical structures
and exploiting their mismatched features.
Nanoscale Tweaks
Graphene is a molecule-thick sheet of carbon atoms; the
nanotubes are like straws made of boron and nitrogen. Yap and his team
exfoliate graphene and modify the material’s surface with tiny pinholes. Then
they can grow the nanotubes up and through the pinholes. Meshed together like
this, the material looks like a flake of bark sprouting erratic, thin hairs.
“When we put these two aliens together, we create something
better,” Yap says, explaining that it’s important that the materials have
lopsided band gaps, or differences in how much energy it takes to excite an
electron in the material. “When we put them together, you form a band gap
mismatch—that creates a so-called ‘potential barrier’ that stops electrons.