Efforts to utilize the high intrinsic thermal conductivity of carbon nanotubes (CNTs) for thermal transport applications, namely for thermal interface materials (TIMs), have been encumbered by the presence of high thermal contact resistances between the CNTs and connecting materials. Here, a pyrenylpropyl‐phosphonic acid surface modifier is synthesized and applied in a straight forward and repeatable approach to reduce the thermal contact resistance between CNTs and metal oxide surfaces. When used to bond nominally vertically aligned multi‐walled CNT forests to Cu oxide surfaces, the modifier facilitates a roughly 9‐fold reduction in the thermal contact resistance over dry contact, enabling CNT‐based TIMs with thermal resistances of 4.6 ± 0.5 mm2 K W−1, comparable to conventional metallic solders. Additional experimental characterization of the modifier suggests that it may be used to reduce the electrical resistance of CNT‐metal oxide contacts by similar orders of magnitude.

Vertical carbon nanotube (CNT) forests bonded at room temperature with sprayed on nanoscale polymer coatings are found by measurement to produce thermal resistances that are on a par with those of conventional metallic solders. These results are achieved by reducing the high contact resistance at CNT tips, which has hindered the development of high performance thermal interface materials based on CNTs. A spray coating process is developed for depositing nanoscale coatings of polystyrene and poly-3-hexylthiophene onto CNT forests, as a bonding agent that mitigates thermal resistance by enhancing the area available for heat transfer at CNT contacts. Resistances as low as 4.9 ± 0.3 mm(2) K W(-1) are achieved for the entire polymer coated CNT interface structure. The suitability of the spray coating process for large-scale implementation and the role of polymer and CNT forest thickness in determining the thermal resistance are also examined.

Forests comprised of nominally vertically aligned carbon nanotubes (CNTs) are excellent candidates for thermal interface materials (TIMs) due to their theoretically predicted outstanding thermal and mechanical properties. Unfortunately, due to challenges in the synthesis and characterization of these materials reports of the thermal conductivity and thermal contact resistance of CNT forests have varied widely and typically fallen far short of theoretical predictions. In particular, the micro- and nano-length scales characteristic of the heat transfer in CNT forests pose significant challenges and may lead to misreported results. Here we examine the ability of a popular and well-established thermal metrology technique, time-domain thermoreflectance (TDTR), to resolve the properties of CNT forest TIMs. The characteristic heating frequencies of TDTR (1–10 MHz) are used to probe heat transfer at length scales spanning ∼0.1–1 μm, applicable for measuring the contact resistance between the CNT forest free tips and an opposing substrate. We identify the range of CNT forest-opposing substrate interface resistances that can be resolved with TDTR, and simultaneously demonstrate the effectiveness of several processes developed to reduce the resistance of these interfaces. The limitations of characterizing CNT forests with TDTR are discussed in terms of uncertainty and sensitivity to parameters of interest.

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Forests comprised of nominally vertically aligned carbon nanotubes (CNTs), having outstanding thermal and mechanical properties, are excellent candidates for thermal interface materials (TIMs). However, the thermal performance of CNT forest TIMs has been limited by the presence of high thermal contact resistances at the CNT tip interface. The high thermal contact resistance at the CNT tip interface stems from two sources: (1) the relatively weak van der Waals type bonding, which impedes phonon transport, and (2) low contact area. In this work we will show that common solvents, such as water, can be applied to the CNT forest to increase the contact area and reduce the contact resistance by an average of 75%. Specifically, there are two likely mechanisms that can increase the contact area when a CNT forest is wet with a fluid and compressed in an interface. The first is relaxing the van der Waals interactions between contacting CNTs within the forest, consequently decreasing the stiffness of the forest and allowing it to better conform to the opposing surface. The second is the pulling of CNT tips through capillary interactions into contact with the opposing surface as the solvent evaporates. By measuring the thermal resistance of CNT TIMs before and after soaking in variety of solvents the capacity of each mechanism for reducing the contact resistance is explored.