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John O | January 2017

Rice scientists calculate graphene nano-chimneys to cool circuits


rice university scientists have calculated that placing a con-like nanoscale chimney structure between graphene and carbon nanotubes will eliminate the barrier of heat escaping and will in turn create a path for using these structures to dissipate heat from electronic components.

 

nanochimneys_600

rice researchers simulated nanochimneys to connect graphene and carbon nanotubes. (rice university)

 

graphene and carbon nanotubes both consist of six-atom rings, according to a report on then rice website, but when graphene is used to grow nanotubes it forms seven-atom rings, which has proven to be beneficial for storing hydrogen but the heptagonal rings scatter phonons rather than directing them through the nanotube structures.

 

using computer simulations, the rice researchers have theorized that removing an atom from the rings would “force a cone to form between the graphene and the nanotube.”

 

the article continued, “the geometric properties (aka topology) of the graphene-to-cone and cone-to-nanotube transitions require the same total number of heptagons, but they are more sparsely spaced and leave a clear path of hexagons available for heat to race up the chimney.”

 

the simulations tested phonon conduction through free-standing nanotubes, pillared graphene, and nano-chimneys with a cone radius of 20-40 angstroms. pillared graphene was 20 percent less conductive than plain nanotubes, but the 40-angstrom cones were 20 percent more conductive.

 

the work was recently published in the journal of physical chemistry c. the abstract from the report stated:

 

“pillared 3d carbon architectures, with the graphene layers and carbon nanotubes connected by topological junctions, have been produced and observed, as reported recently. however, the atomistic details of such junctions are hard to discern in microscopy and remain presently unclear.

 

“the simplest junction contains six heptagons in the transition region between the nanotube and graphene. although these junctions make the pillared architectures possible, they are susceptible to failure when the whole structure undergoes mechanical or thermal stress.

 

“in this work we consider ‘nanochimneys’, a variety of special junctions with cones in between the nanotube and graphene parts. we explore the structures of the nanochimneys (ncs) and determine their underlying topological requirements. we also study the thermal conductance of these pillared architectures and show that ncs conduct heat better than regular simple junctions.”

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