Superior thermal interface via vertically aligned carbon nanotubes grown on graphite foils
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Ajit K. Roy Nanoelectronic Materials Branch, Materials & Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio 45433
Robert Wheeler UES Inc., Dayton, Ohio 45432
Vikas Varshney Nanoelectronic Materials Branch, Materials & Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio 45433; and Universal Technology Corporation, Dayton, Ohio 45432
Feng Du and Liming Dai Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio 44106 (Received 26 April 2012; accepted 12 November 2012)
In an attempt to study the thermal transport at the interface between nanotubes and graphene, vertically aligned multiwalled carbon nanotubes (CNTs) were grown on graphite thin film substrates. A systematic cross-sectional probing of the materials’ morphology of the interface by scanning electron microscopy and high-resolution transmission electron microscopy revealed that an excellent bond existed between the nanotubes and the substrate along some fraction of interface. Imaging and electron diffraction analyses performed at the boundary reveal a polycrystalline interfacial structure. Compositional probing along the interface by energy dispersive x-ray spectroscopy revealed that there were no catalyst particles or other impurities present. The estimated interfacial thermal resistance of lower than 5–7.5 (mm2 K)/W suggests that this type of CNT/graphite interface could open up multiple routes toward the designing and development of advanced thermal interface materials for aerospace and nano-/microelectronics applications. I. INTRODUCTION
The growing emergence of wide band gap semiconductors for power, radio-frequency (RF) electronics, and high power silicon microelectronics has accentuated the need for improved thermal interface materials (TIMs) in providing efficient management of the huge thermal load generated by these devices. The existing TIMs commonly used for such applications can be categorized as thermal grease-type interface materials, thermally conductive adhesives, and thermal tapes. In most thermal greases, high thermal conductivity originates from the filler particles, such as aluminum or silver powder. The thermal conductivity of the best thermal greases is on the order of 8–10 W/(m K).1 Further, thermal greases are usually oil-based materials so their application is messy and difficult to apply in a thin uniform coating. In addition, these greases are not reusable and usually suffer from drying or voiding within the interface in applications that involve a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.401 J. Mater. Res., Vol. 28, No. 7, Apr 14, 2013
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high temperatures or extensive thermal cycling. This eventually increases the thermal barrier in a significant manner. On the other hand, thermal transport properties of thermal tapes and thermally conductive adhesives do not meet the thermal management and structural load requirements of the next generation ae
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