Engineering interfaces in carbon nanostructured mats for the creation of energy efficient thermal interface materials Ronald J. Warzoha, Di Zhang, Gang Feng, Amy S. Fleischer * Department of Mechanical Engineering, Villanova University, Villanova, PA 19085, USA ARTICLE INFO Article history: Received 25 January 2013 Accepted 14 May 2013 Available online 23 May 2013 ABSTRACT One of the few remaining opportunities to increase heat dissipation in IC circuitry is to sub- stantially decrease the thermal interface resistance between solid–solid contacts from source to sink. In this study, heterogeneous nanostructured mats (1–100 lm thick, ran- domly oriented networks of nanostructures) are synthesized for use as thermal interface materials (TIMs). Recent studies suggest that mats composed entirely of carbon nanotubes (CNTs) or graphite nanofibers (GNFs) can act as thermal insulators due to significant pho- non scattering at interfaces. In this work, graphene nanoplatelets (xGnPs) with high surface areas are included in CNT and GNF mats in order to increase the contact area between nanostructures and mitigate phonon scattering. Results indicate that an increase in con- tact area between nanostructures increases the thermal conductance across nanostructure networks by nearly an order of magnitude. Additionally, a study of the surface topography of CNT and GNF mats using atomic force microscopy (AFM) indicates that they are able to conform well to the asperities between rough, mating surfaces. Thus, an increase in con- tact area between CNT junctions not only produces a thermally conductive network, but also increases the reliability of a CNT mat TIM by avoiding common issues associated with the use of wetting agents. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Thermal management techniques for electronics applications are fast approaching their performance limits as the pace of technology scaling of integrated circuitry (IC) continues una- bated. However, one realm in which significant improve- ments can still be achieved is at component interfaces. At these interfacial regions, mismatched surface asperities cre- ate micron-sized pockets of air between solid components. Due to the very low thermal conductivity of air (k air = 0.026 - W/m K at 300 K [1]), these surface asperities result in a sharp temperature difference at the interface. In order to reduce the temperature across the interface, thermal engineers rely on the insertion of a highly deformable, thermally conductive material (or thermal interface material (TIM)) between the mating surfaces. In an effort to develop novel TIMs, research- ers have recently turned their attention to the implantation of highly conductive carbon nanostructures into ‘‘wetting agents’’ [2–8]. ‘‘Wetting agents’’, like PCMs and thermal greases, are typically used to connect mating materials be- cause they are able to conform well to the material’s surface asperities. Carbon nanotubes (CNTs) and nanofibers (CNFs) have been of particular interest for use in TIMs due to their high intrinsic thermal conductivities and low densities [9– 11]. Few layer graphene (FLG) has also been of interest lately as a filler material for thermal interface applications [6]. Bal- 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.05.028 * Corresponding author. E-mail address: amy.fleischer@villanova.edu (A.S. Fleischer). CARBON 61 (2013) 441 – 457 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon