Isolated individual carbon nanotubes (CNTs) have shown exceptional thermal conductivity along their axis, but have
poor thermal transfer between adjacent CNTs. Thick bundles of aligned CNTs have been used as heat pipes, but the
thermal input and output areas are the same, providing no heat spreading effect. Energetic argon ion beams are used to
join, or cross-link overlapping CNTs in a thick film to form an interpenetrating network with an isotropic thermal
conductivity of 2150 W/m-K. Such thick films may be used as heat spreaders to enlarge the thermal footprint of various
electronic and semiconductor devices, laser diodes and CPU chips, for example, to enhance cooling.