A slight atomic adjustment creates a cone-like “chimney” between the graphene and nanotube to give heat a way to escape



Cooling and other issues
derived from scaling continue to obstruct nanoelectronics from reaching their
full disruptive potential. Preventing the heat build-up at the nanoscale from
damaging embedded electronics remains challenging, but researchers from Rice
University determined that a few nanoscale adjustments enable graphene-carbon nanotube
junctions to excel at transferring heat away from nanoelectronics and
preventing structural damage.

In theory, all it takes is
building a cone-like “chimney” between the graphene and nanotube to give heat a
way to escape. That’s what Rice University theoretical physicist Boris Yakobson
claims in a research paper published in the American Chemical Society’s Journal
of Physical Chemistry C.

Graphene nanotubes, like
carbon nanotubes, excel at rapidly transferring electricity and phonons — atoms
or molecules in condensed matter that collectively behave in an excitation
state to create physical properties like electrical conductivity. Both types of
nanotubes consist of six-atom rings that form a chicken wire-like mesh, but
when a nanotube is grown from the graphene itself, the atoms create a
seven-sided heptagonal ring that’s excellent for storing hydrogen for energy
applications but scatters phonons and restricts the release of heat.

Yakobson and his team
discovered — by way of simulation — that removing atoms from specific points in
the two-dimensional graphene base forces a cone to form between the graphene
and the nanotube. The resulting geometric properties require the same number of
total heptagons and leave a clear path for the dissipation of heat from

“Our interest in advancing new
applications for low-dimensional carbon — fullerenes, nanotubes, and graphene —
is broad,” Yakobson said. The “chimneys” may be used as building blocks to fill
three-dimensional spaces with different designs, “creating anisotropic,
non-uniform scaffolds with properties that none of the current bulk materials
have. In this case, we studied a combination of nanotubes and graphene,
connected by cones, motivated by seeing such shapes obtained in our colleagues’
experimental labs.”

The Rice team’s simulation
tested phonon conduction using free-standing nanotubes, pillared graphene, and
nano-chimneys with a cone radius of 20 or 40 angstroms. Each offered a
different degree of conductivity. The pillar graphene was 20% less conductive
than plain nanotubes, while the 20-angstrom nano-chimneys were as conductive as
the plain nanotubes. The nano-chimney whose diameter measured 40 angstroms
offered a 20% improvement over the nanotubes.

“The tunability of such
structures is virtually limitless, stemming from the vast combinatorial
possibilities of arranging the elementary modules,” said Alex Kutana, a Rice
research scientist and co-author of the study. “The actual challenge is to find
the most useful structures, given a vast number of possibilities, and then make
them in the lab reliably.”

To read Yakobsen’s paper,
visit http://bit.ly/2jUzOEQ.