Isotope Effect on the Thermal Conductivity of Boron Nitride Nanotubes

We have measured the temperature-dependent thermal conductivity $\kappa (T)$ of individual multiwall boron nitride nanotubes using a microfabricated test fixture that allows direct transmission electron microscopy characterization of the tube being measured. $\kappa (T)$ is exceptionally sensitive to isotopic substitution, with a 50% enhancement in $\kappa (T)$ resulting for boron nitride nanotubes with 99.5% ${}^{11}\mathrm{B}$. For isotopically pure boron nitride nanotubes, $\kappa$ rivals that of carbon nanotubes of similar diameter.

Figure 1

(a) A scanning electron microscope image of the microfabricated test fixture with a boron nitride nanotube on it ($\mathrm{\text{scale bar}}=10\mu \mathrm{m}$). The inset shows the corresponding transmission electron microscope image of the same device ($\mathrm{\text{scale bar}}=1\mu \mathrm{m}$). (b) A high-resolution transmission electron microscope image of the boron nitride nanotube ($\mathrm{\text{scale bar}}=5\mathrm{nm}$). (c) The corresponding electron diffraction pattern of the boron nitride nanotube.

Figure 2

The $\kappa (T)$ of a carbon nanotube (open circles), a boron nitride nanotube (BNNT, solid triangles), and an isotopically pure boron nitride nanotube (solid squares) with similar outer diameters.

Figure 3

The $\kappa (290\mathrm{K})$ vs outer diameter of various boron nitride nanotubes (solid triangles) and carbon nanotubes (solid stars). Data from Ref. 13 are also shown for comparison (open circles).