Mar. 4, 2008 – Fujitsu Labs says it has successfully created a nanoscale carbon composite with a self-organizing structure by combining carbon nanotubes and graphene, combining CNTs’ high thermal conductivity and high-current density tolerance with graphene’s high electron mobility. The composite is synthesized at 510°C, cooler than temperatures for conventional graphene that are too high for electronic device applications. Details of the technology are being disclosed at this week’s (March 3-5) 34th Fullerene Nanotubes General Symposium in Nagoya, Japan.
Research is underway to find technologies that can synthesize carbon nanotubes at temperatures as low as 400°C, which would enable use in devices vulnerable to heat. Graphene has been a popular choice as a channel material, but conventional methods for synthesizing it only work at >700°C, or involve stripping away graphite crystals, a time-consuming and unreliable process, the company explained in a statement.
In its work, Fujitsu Labs experimented with CVD, where feedstock gas is heat-cracked into a vacuum chamber to synthesize films or structures on a substrate. They managed to form aligned growth multiwalled carbon nanotubes with layers of graphene on top (from just a few layers to a few dozen) formed in a “self-organizing way,” creating a complex composite (See Fig. 1). It’s the first composite, they say, featuring both 1D and 2D elements based on graphene layers and nanotubes, perpendicularly connected.
Fig 1. (a) Cross-section electron microscopic image of the new nano-scale carbon composite. (b) Electron microscopic image of the graphene multi-layers.
Because the CNTs are linear 1D structures, in the 2D directions perpendicular to the tube axis they have nearly no thermal or electrical conductivity between tubes. But graphene does have these properties in 2D, so the new carbon nanostructure is expected to have electrical conduction and thermal dissipation in all directions.
Also, because these new nanotubes nearly all connect to the graphene with good uniformity at the endpoints, and since the graphene surface is planar (See Fig. 2), the researchers think the nanostructures will enable “excellent electrical and thermal conductivity.”
Fig 2. (Top) Schematic view of the new nano-scale carbon composite. (bottom) Diagram of anticipated structure.
Fujitsu Labs plans to keep exploring the research into how the complex carbon nanostructures form and their physical characteristics, and will pursue development of technologies to enable formation of high-quality carbon nanostructures at a lower temperature.