  The thermal conductivity, k(T), of bulk single-wall carbon nanotubes (SWNT's)
displays a linear temperature dependence at low T that has been attributed to
1D quantization of phonons. To explore this issue further, we have measured the
k(T) of samples with varying average tube diameters. We observe linear k(T) up
to higher temperatures in samples with smaller diameters, in agreement with a
quantization picture. In addition, we have examined the effect of annealing on
k(T). We observe an enhancement in k(T) for annealed samples which we attribute
to healing of defects and removal of impurities. These measurements demonstrate
how the thermal properties of an SWNT material can be controlled by
manipulating its intrinsic nanoscale properties.
