Sandwiched two sheets of graphene encapsulate a platinum growth solution. |
The
Korea Advanced Institute of Science and Technology (KAIST) announced
that a research team from the Department of Materials Science and
Engineering has developed a technology that enables scientists and
engineers to observe processes occurring in liquid media on a scale of
less than a nanometer.
Professor
Jeong Yong Lee and Researcher Jong Min Yuk, in collaboration with
Professor Paul Alivisatos’s and Professor Alex Zettl’s groups at the
University of California, Berkeley, succeeded in making a graphene
liquid cell or capsule, confining an ultra-thin liquid film between
layers of graphene, for real-time and in situ imagining of nanoscale
processes in fluids with atomic-level resolution by a transmission
electron microscope (TEM). Their research was published in the April 6,
2012 issue of Science.
The
graphene liquid cell (GLC) is composed of two sheets of graphene
sandwiched to create a sealed chamber where a platinum growth solution
is encapsulated in the form of a thin slice. Each graphene layer has a
thickness of one carbon atom, the thinnest membrane that has ever been
used to fabricate a liquid cell required for TEM.
The
research team peered inside the GLC to observe the growth and dynamics
of platinum nanocrystals in solution as they coalesced into a larger
size, during which the graphene membrane with the encapsulated liquid
remained intact. The researchers from KAIST and the UC Berkeley
identified important features in the ongoing process of the
nanocrystals’ coalescence and their expansion through coalescence to
form certain shapes by imaging the phenomena with atomic-level
resolution.
Professor
Lee said, “It has now become possible for scientists to observe what is
happening in liquids on an atomic level under transmission electron
microscopes.”
Researcher Yuk, one of the first authors of the paper, explained his research work.
“This
research will promote other fields of study related to materials in a
fluid stage including physical, chemical, and biological phenomena at
the atomic level and promises numerous applications in the future.
Pending further studies on liquid microscopy, the full application of a
graphene-liquid-cell (GLC) TEM to biological samples is yet to be
confirmed. Nonetheless, the GLC is the most effective technique
developed today to sustain the natural state of fluid samples or species
suspended in the liquid for a TEM imaging,” say Yuk.
The
transmission electron microscope (TEM), first introduced in the 1930s,
produces images at a significantly higher resolution than light
microscopes, allowing users to examine the smallest level of physical,
chemical, and biological phenomena. Observations by TEM with atomic
resolution, however, have been limited to solid and/or frozen samples,
and thus it has previously been impossible to study the real time fluid
dynamics of liquid phases.
TEM
imaging is performed in a high vacuum chamber in which a thin slice of
the imaged sample is situated, and an electron beam passes through the
slice to create an image. In this process, a liquid medium, unlike solid
or frozen samples, evaporates, making it difficult to observe under
TEM.
Attempts
to produce a liquid capsule have thus far been made with
electron-transparent membranes of such materials as silicon nitride or
silicon oxide; such liquid capsules are relatively thick (tens to one
hundred nanometers), however, resulting in poor electron transmittance
with a reduced resolution of only a few nanometers. Silicon nitride is
25 nm thick, whereas graphene is only 0.34 nm.
Graphene,
most commonly found in bulk graphite, is the thinnest material made out
of carbon atoms. It has unique properties such as mechanical tensile
strength, high flexibility, impermeability to small molecules, and high
electrical conductivity. Graphene is an excellent material to hold
micro- and nanoscopic objects for observation in a transmission electron
microscope by minimizing scattering of the electron beam that
irradiates a liquid sample while reducing charging and heating effects.
High-Resolution EM of Colloidal Nanocrystal Growth Using Graphene Liquid Cells
Source: KAIST
