The ability to quickly move the heat generated by integrated circuits cannot be overvalued as too much heat can cause critical errors. Two materials that could be very useful in getting heat away from circuits are graphene and carbon nanotubes, but combining them to any great effect has proven difficult thus far. Researchers at Rice University though appear to have solved the problem by creating nano-chimneys.
Both graphene and nanotubes are made of pure carbon and consist of hexagonal rings, like chicken wire, and both are able to transmit heat very quickly. Combining these materials stunts that transmission though, with pillared graphene being 20% less conductive than free-standing nanotubes. This is because when the nanotubes are grown from graphene, heptagonal, seven-member rings form to connect the two structures. These rings, however, scatter phonons carrying thermal energy, preventing the heat from escaping. What the researchers discovered is that by selectively removing atoms from the graphene base a cone will be formed to connect the graphene and nanotubes, and these cones allow the heat to move up the nanotubes and away from the graphene. The cones do not reduce the number of heptagons but make them sparser, leaving paths for the phonons to take.
The researchers simulated nano-chimneys with cone radii of 2 nm and 4 nm to compare them to free-standing nanotubes and pillared graphene. The 2 nm-base chimneys were as conductive as the free-standing nanotubes while the 4 nm-base chimneys were 20% more conductive, which indicates there is a mechanism to tune the conductivity of these structures.
Source: Rice University
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