(November 3, 2015) Ultrasensitive
gas sensors based on the infusion of boron atoms into graphene -- a tightly
bound matrix of carbon atoms -- may soon be possible, according to an
international team of researchers from six countries.
Graphene is known for its remarkable strength and ability to
transport electrons at high speed, but it is also a highly sensitive gas
sensor. With the addition of boron atoms, the boron graphene sensors were able
to detect noxious gas molecules at extremely low concentrations, parts per
billion in the case of nitrogen oxides and parts per million for ammonia, the
two gases tested to date. This translates to a 27 times greater sensitivity to
nitrogen oxides and 10,000 times greater sensitivity to ammonia compared to
pristine graphene. The researchers believe these results, reported today (Nov.
2) in the Proceedings of the National Academy of Sciences, will open a path to
high-performance sensors that can detect trace amounts of many other molecules.
"This is a project that we have been pursuing for the
past four years, " said Mauricio Terrones, professor of physics, chemistry
and materials science at Penn State. "We were previously able to dope
graphene with atoms of nitrogen, but boron proved to be much more difficult.
Once we were able to synthesize what we believed to be boron graphene, we
collaborated with experts in the United States and around the world to confirm
our research and test the properties of our material."
Both boron and nitrogen lie next to carbon on the periodic
table, making their substitution feasible. But boron compounds are very air
sensitive and decompose rapidly when exposed to the atmosphere.
One-centimeter-square sheets were synthesized at Penn State in a one-of-a-kind
bubbler-assisted chemical vapor deposition system. The result was large-area,
high-quality boron-doped graphene sheets.
Once fabricated, the researchers sent boron graphene samples
to researchers at the Honda Research Institute USA Inc., Columbus, Ohio, who
tested the samples against their own highly sensitive gas sensors. Konstantin
Novoselov's lab at the University of Manchester, UK, studied the transport
mechanism of the sensors. Novoselov was the 2010 Nobel laureate in physics.
Theory collaborators in the U.S. and Belgium matched the scanning tunneling
microscopy images to experimental images, confirmed the presence of the boron
atoms in the graphene lattice and their effect when interacting with ammonia or
nitrogen oxide molecules. Collaborators in Japan and China also contributed to
the research.