Tech Briefs Magazine - August 2024 - 24

highly selective membranes targeting
special substances.
The study reveals that adsorption in
membrane nanopores does not only depend
on the adsorption surface and the
limited mass transfer, but also on the interplay
of hydrodynamic forces, friction,
and the forces of attraction and repulsion
at the liquid-wall interface. Highly
water-permeable nanopores exhibit low
interaction due to the small friction and
the high flow rate.
" When the molecules are not retained
because of their size, interaction with the
material will often determine what happens.
The molecules will bounce through
the membrane similar to a climber climbing
a wall. This is much easier when there
are many good climbing holds, " said
Schäfer. Studies like that performed by
IAMT help to specifically design pore geometry
and pore surface structure.
The membranes were developed by Dr.
Francesco Fornasiero and his team at
LLNL. The experiments with the micropollutants
were carried out and evaluated using
latest analytical instruments at IAMT.
The study was the first to focus on the
interplay of hydrodynamic forces, friction,
and forces of attraction and repulsion.
It provides basic findings with respect
to water processing. These may
benefit ultra- and nanofiltration processes
controlled by nanopores.
For more information, contact Monika
Vertically aligned carbon nanotubes make up an ideal membrane to study the interplay of forces in
nanopores. (Image: IAMT, KIT)
Landgraf at presse@kit.edu; +49 721608-41150.
Oxygen-Free
Chemical Vapor Deposition Method to Make
Graphene
Engineers have linked oxygen to graphene quality and developed new techniques to
reproducibly make the wonder material at scale.
Columbia University, New York, NY
G
raphene has been called " the
wonder material of the 21st century. "
But graphene has a dirty little
secret: it's dirty. Now, engineers at Columbia
University and colleagues at
the University of Montreal and the
National Institute of Standards and
Technology are poised to clean things
up with an oxygen-free chemical vapor
deposition (OF-CVD) method
that can create high-quality graphene
samples at scale. Their work, published
in Nature, directly demonstrates
how trace oxygen affects the
growth rate of graphene and identifies
the link between oxygen and
graphene quality for the first time.
" We show that eliminating virtually
all oxygen from the growth process is
the key to achieving reproducible,
high-quality CVD graphene synthesis, "
said Senior Author and Professor James
Hone. " This is a milestone towards largescale
production of graphene. "
Graphene has historically been synthesized
in one of two ways. There's the
24
desirable
The Hone lab at Columbia Engineering created over 100
identical graphene samples
with
their
oxygen-free
chemical vapor deposition method. (Image: Jacob
Amontree and Christian Cupo, Columbia University)
" scotch-tape " method, in which individual
layers are peeled from a bulk sample
of graphite (the same material you'll
find in pencil lead) using household
tape. Such exfoliated samples can be
quite clean and free from impurities that
would otherwise interfere with graphene's
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properties. However, they
tend to be too small - just a few tens
of micrometers across - for industrial-scale
applications and, thus, better
suited for lab research.
To move from lab explorations to
real-world applications, researchers
developed a method to synthesize
large-area graphene about 15 years
ago. This process, known as CVD
growth, passes a carbon-containing
gas, such as methane, over a copper
surface at a temperature high enough
(about 1,000 °C) that the methane
breaks apart and the carbon atoms
rearrange to form a single honeycomb-shaped
layer of graphene. CVD
growth can be scaled up to create
graphene samples that are centimeters
or even meters in size. However, despite
years of effort from research groups
around the world, CVD-synthesized samples
have suffered from problems with
reproducibility and variable quality.
The issue was oxygen. In prior publications,
Co-Authors Richard Martel and
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