Atomic Layer Deposition on Quantities of Multiwalled Carbon Nanotubes
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Atomic Layer Deposition on Quantities of Multiwalled Carbon Nanotubes Andrew S. Cavanagh1, Christopher A. Wilson2, Alan W. Weimer3, and Steven M. George2,3 1 Dept. of Physics, University of Colorado, Boulder, CO, 80309 2 Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, CO, 80309 3 Dept. of Chemical and Biological Engineering, University of Colorado, Boulder, CO, 80309 ABSTRACT Atomic layer deposition (ALD) was performed on quantities of multiwalled carbon nanotubes (MWCNTs) in a rotary reactor. Because of nucleation difficulties, Al2O3 ALD grew as nanospheres on the MWCNTs. After a NO2 nucleation treatment, Al2O3 ALD films grew conformally and noncovalently functionalized the surface of the MWCNT. This Al2O3 ALD film served as a platform for the growth of W ALD metal. The uncoated and ALD-coated MWCNTs were characterized with transmission electron microscopy and x-ray photoelectron spectroscopy. This study demonstrates that ALD can be performed on quantities of very high surface area MWCNT substrates. INTRODUCTION Atomic layer deposition (ALD) can be used to coat and functionalize the surface of gram quantities of carbon nanotubes (CNTs). ALD is a method of thin film growth using sequential, self limiting surface reactions [1, 2]. In one ALD cycle, precursor “A” is reacted with the substrate surface to add a species of interest and to introduce a new surface functional group. In the second step, precursor “B” adds a second species to the surface and returns the surface to its original functionalization. Together steps “A” and “B” comprise one ALD cycle. These ABAB… ALD cycles are repeated to achieve the desired film thickness. ALD has been reported for many materials [3]. ALD is well suited for growing thin conformal films on high aspect ratio structures [4]. ALD Al2O3 growth has been demonstrated on individual single-walled carbon nanotubes (SWCNTs) [5] and multiwalled carbon nanotubes (MWCNTs) [6]. ALD Al2O3 growth has also been demonstrated on trace quantities of MWCNTs [7]. The nucleation of Al2O3 ALD on SWCNT surfaces has been identified as a problem [8]. The solution to the nucleation problem was the formation of an adsorbed layer of NO2 and trimethyl aluminum (TMA) on the CNT surface [5]. This noncovalently bonded layer served as a platform for the growth of Al2O3 ALD. CNT/polymer composites may have many useful properties. ALD growth on gram quantities of CNTs is needed to generate sufficient material to test the properties of the resulting CNT/composite. These CNT/composites may have high mechanical strength, high thermal and electrical conductivity and high stability. Possible applications for CNT/polymer composites include flexible electrostatic dissipation films, transparent conductive coatings, electromagnetic interference shielding and ultra light structural materials. There are many examples of CNT/polymer composites in the literature [9-13]. However, the dispersion of CNTs in the polymer composite is a difficulty and may limit the CNT/polymer composite properties. T
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