Fabrication of thermally-conductive carbon nanotubes-copper oxide heterostructures
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Fabrication of thermally-conductive carbon nanotubes-copper oxide heterostructures Yuan Li1 and Nitin Chopra1* 1 Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL 35401 U.S.A. *Corresponding Author E mail: [email protected], Tel: 205-348-4153, Fax: 205-348-2164 ABSTRACT A complete dry processing route is developed for the fabrication of thermally-conductive carbon nanotube (CNT)-copper oxide (CuOx) heterostructures. This was achieved by the deposition of copper (Cu) onto CNTs and subsequent annealing in Ar and air environment to convert the coated Cu into CuOx nanoparticles. The survivability and diameters of CNTs were studied to ensure their integrity after the multiple processing steps and annealing temperatures (400 oC). The as-produced CNTs, air/Ar-annealed CNTs, Cu-coated CNTs, and CNT-CuOx heterostructures were characterized to study their structure, phase, and morphology using microscopy, elemental analysis, X-ray diffraction, and sheet resistance. It was observed that CNTs could survive the processing conditions and became coated with CuOx nanoparticles. The sheet resistance of CNTs coated with CuOx nanoparticles was ~4 times greater than the asproduced CNTs. The Raman spectroscopy-based estimation of thermal conductivity of CNTs and CNT-CuOx heterostructures showed 2-7 times enhancement for the latter as compared to pure CuOx. In conclusion, such hybrid CNT-based heterostructures are promising for applications in thermal management. INTRODUCTION Carbon nanotubes (CNTs) are promising for applications in nanoelectronics, interconnects, energy, and sensors due to their remarkable properties [1-4]. In addition, CNTs exhibit superior thermal conductivities, as high as 2000 W/m-K to 6000 W/m-K [5-8], 10 times higher than copper and silver. It is of particular interest to develop novel nanocomposites or heterostructures comprised of CNTs and conventional materials such as copper (Cu) or its oxides (CuOx), where the latter are known to have low thermal conductivities. These could be potentially of use as nanofillers, thermal fluid, and multifunctional interconnects [9-11]. Such nanocomposites could allow for tunability of thermal conductivity of the hybrid materials by modulating composition, structure, interface, and morphology of the heterostructured components. Here, we demonstrate a dry processing route for controlled fabrication of CNTCuOx heterostructures. In addition, we study the thermal conductivities of these heterostructures. EXPERIMENT Materials and Methods: Xylene and ferrocene were used as the carbon source for CNT growth and were purchased from Fisher Scientific (Pittsburgh, PA). Acetone and ethanol were purchased from VWR (Atlanta, GA). DI water (18.1 M -cm) was obtained using a Barnstead International DI water system (E-pure D4641). All chemicals were used without further purification. Silicon (Si) wafers (, n-type) were purchased from IWS (Colfax, CA). Dispersion of heterostructures into ethanol was carried out in a Branson 2510 Sonicator (Danbury, CT). ATC
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