Thermal Conductivity of Copper-Graphene Composite Films Synthesized by Electrochemical Deposition with Exfoliated Graphe
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LOW-COST manufacturing of thermal interface materials and heat spreaders with high capacity to dissipate thermal energy is of significant importance in nanoelectronics and high-frequency and high-power devices such as power amplifiers and laser diodes.[1–3] The thermal conductivity of diamond,[4] graphite,[5] carbon nanotubes (CNTs),[6] and graphene[7,8] is higher compared with other materials. Of these, the measurements at room temperature showed that the thermal conductivity of free-standing graphene is the highest with the value between 3000 and 5000 W/m.K and, thus, greater than that of other forms of carbon discovered until now. However, it was also shown recently[9] that the thermal conductivity of monolayer of graphene supported on SiO2 is only 600 W/m.K as a result of phonon leaking and phonon scattering by the substrate. To alleviate the problems associated with low thermal conductivity thermal interface materials[10] (TIM), recently we studied a simple method of processing In-graphene and In-Ga-graphene composites[11,12] and found that the thermal conductivity at 300 K (27 °C) is improved by a factor of 2.5 and 3, respectively, compared with that of In and In-Ga. In general, a heat spreader system contains a high capacity heat spreader and an external cooling system in addition to the TIM attached to the active device region. In the current work, K. JAGANNADHAM, Associate Professor, is with the Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695. Contact e-mail: [email protected] Manuscript submitted August 14, 2011. Article published online November 10, 2011. 316—VOLUME 43B, APRIL 2012
we studied the preparation of copper-graphene (Cu-gr) composite heat spreaders by electrochemical codeposition from CuSO4 solution with graphene oxide suspension. The thermal conductivity of the Cu-gr composites was determined experimentally and modeled to determine the importance of interface thermal conductance and graphene particle size.
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EXPERIMENTAL PROCEDURES
The preparation of copper-graphene composite samples has been described at length in the previous work.[11,13] A brief description is provided here. Graphene oxide (GO) films were prepared by chemical exfoliation from microcrystalline graphite[14] supplied by Asbury Graphite Inc. (Asbury, NJ) The details of preparation of exfoliated GO are discussed at length in our previous work.[11] A suspension of GO particulates in a 0.2 M solution of CuSO4 was prepared. Electrochemical codeposition from a bath containing graphene oxide (GO) suspension in a solution of technical grade CuSO4 in distilled water was carried out on oxygen-free high-conductivity (OFHC) copper foils. The pH was maintained close to 7, and a low current density of 1.75 mA/cm2 and growth rate of 2 to 3 lm/h[13] were used with a pure Cu anode to achieve smooth films. GO is hydrophobic on the basal plane and hydrophilic at the edges so that the suspension of the GO particulates is maintained at pH > 6.[15] Five samples of Cu-graphene (Cu-gr)
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