A single gold
plasmonic nanoantenna probes the hydrogen absorption in an adjacent
palladium
nanocube. Illustration by Ella Marushchenko and Alex Tokarev.
(September 8, 2015) Scientists
at Chalmers University of Technology have developed a new way to study
nanoparticles one at a time, and have discovered that individual particles that
may seem identical in fact can have very different properties. The results,
which may prove to be important when developing new materials or applications
such as hydrogen sensors for fuel cell cars, will be published in Nature
Materials.
— We were able to show that you gain deeper insights into
the physics of how nanomaterials interact with molecules in their environment
by looking at the individual nanoparticle as opposed to looking at many of them
at the same time, which is what is usually done, says Associate Professor
Christoph Langhammer, who led the project.
By applying a new experimental approach called plasmonic
nanospectroscopy, the group studied hydrogen absorption into single palladium
nanoparticles and found that particles with exactly the same shape and size may
exhibit differences as great as 40 millibars in the pressure at which hydrogen
is absorbed. The development of sensors that can detect hydrogen leaks in fuel
cell powered cars is one example of where this new understanding could become
valuable in the future.
— One main challenge when working on hydrogen sensors is to
design materials whose response to hydrogen is as linear and reversible as
possible. In that way, the gained fundamental understanding of the reasons
underlying the differences between seemingly identical individual particles and
how this makes the response irreversible in a certain hydrogen concentration
range can be helpful, says Langhammer.
Others have looked at single nanoparticles one at a time,
but the new approach introduced by the Chalmers team uses visible light with
low intensity to study the particles. This means that the method is
non-invasive and does not disturb the system it is investigating by, for
example, heating it up.
— When studying individual nanoparticles you have to send
some kind of probe to ask the particle ‘what are you doing?’. This usually
means focusing a beam of high-energy electrons or photons or a mechanical probe
onto a very tiny volume. You then quickly get very high energy densities, which
might perturb the process you want to look at. This effect is minimized in our
new approach, which is also compatible with ambient conditions, meaning that we
can study nanoparticles one at a time in as close to a realistic environment as
possible.