Low-temperature heat capacity of modified multiwalled carbon nanotubes with diameter 9.4 nm

The low-temperature specific heat C(T) of multiwalled carbon nanotubes (MWCNTs) with mean outer diameter 9.4 nm, subjected to grinding and grinding-oxidation modifications, was measured from 1.8 K to 275 K. A comparative analysis was performed against initial MWCNTs, bundles of single-walled carbon nanotubes (SWCNT) and graphite. Results indicate that grinding of oxidized MWCNTs increases specific heat relative to initial MWCNTs, maintaining a similar temperature dependence. In contrast, grinding of initial MWCNTs causes different C(T) behavior below 5 K. Above 60 K, the C(T) of all MWCNTs variants, SWCNTs bundles, and graphite converge, reflecting the dominance of 2D graphene sheet phonon density of states. Discrepancies below 60 K are attributed to structural symmetries, potential energies of interaction between walls/sheets/tubes, layer/wall numbers, and defects.