Linear specific heat of carbon nanotubes

The specific heat and thermal conductivity of millimeter-long aligned carbon multiwall nanotubes (MWNT's) have been measured. As a rolled-up version of graphene sheets, a MWNT of a few tens nm diameter is found to demonstrate a strikingly linear temperature-dependent specific heat over the entire temperature range measured (10--300 K). The results indicate that interwall coupling in MWNT's is rather weak compared with its parent form, graphite, so that one can treat a MWNT as a few decoupled two-dimensional single wall tubules. The thermal conductivity is found to be low, indicating the existence of substantial amounts of defects in the MWNT's prepared by a chemical-vapor-deposition method.