Nanoelectronics: Nanotubes throw their heat around.

news & views atoms accumulating at lower temperatures. They find that the binding energy for xenon on a nanotube is 30% lower than for xenon on graphite, and explain this difference in terms of reduced van der Waals interactions (due to the surface of the nanotube being curved and containing only one layer of carbon atoms, whereas graphite is flat and contains several layers of carbon atoms). The movement of atoms and molecules along the nanotube is a double-edged sword. For researchers building mechanical mass spectrometers it is one more potential source of noise and error (although it might be possible to modify the carbon lattice to create trapping sites that will stop this movement and improve performance). However, the fact that atoms can move on the surface, combined with the extraordinary mass resolution that is available, means that surface scientists will be able to study a wide variety of processes and phenomena — such as nucleation processes in thin-film growth and the dynamics of monolayer formation — at the level of single atoms and single-adsorption sites. W hen carbon nanotubes and graphene are described as attractive electronic materials, it is usually because of their high carrier mobilities 1,2 and atomic-scale dimensions, which are characteristics expected to aid efforts to reduce the size of electronics 3,4. However, the potential impact of such carbon nanostructures for thermal management — arguably an equally important challenge facing the electronics community — is less clear. Writing in Nature Nanotechnology, John Cumings and co-workers at the University of Maryland, College Park report that they have discovered a surprising new facet of charge transport in one dimension: a direct current passing through a carbon nanotube can heat the substrate under the nanotube, but leave the nanotube itself cool 5. The Maryland researchers overcame significant experimental difficulties to prove that this effect, which they call remote Joule heating, was occurring. First they prepared and deposited pristine nanotubes, to avoid defects that would otherwise create thermal hotspots. Second, they minimized the effect of contact resistance by increasing the area of overlap between the nanotube and the metal contact relative to that between the nanotube and the substrate. This was important because the low thermal and electrical resistivities of carbon nanotubes would cause the electrode contacts to dominate resistivity data. Finally, the researchers used a technique called electron thermal microscopy (EThM) to measure the temperatures of their nanotube, substrate …