Synthesis of millimeter-long vertically aligned carbon nanotube arrays on aluminum oxide buffer prepared by layer-by-layer assembly of boehmite nanoplates

To synthesize vertically aligned carbon nanotube (VA-CNT) arrays longer than a millimeter using chemical vapor deposition (CVD), aluminum oxide buffer has to be deposited on supporting substrates to prevent diffusion and aggregation of catalyst nanoparticles. Currently, reliable deposition has to be made using expensive and time-consuming e-beam evaporation or thermal sputtering. Here, we report a simple, low-cost, and scalable method for buffer preparation using layer-by-layer assembly of boehmite nanoplates followed by thermal annealing. On top of buffer prepared using this method, we have grown VA-CNT arrays consisting of CNTs with a length of 1.3(±0.1) mm, an inner diameter of 5.6(±1.3) nm, and a wall number of 4(±1) by using CVD with iron as catalyst and ethylene as carbon source. 2013 Elsevier Ltd. All rights reserved. Vertically aligned carbon nanotube (VA-CNT) arrays have attracted increasing attention as new materials for making field emission displays, microfluidic devices, gas sensors, electrochemical double layer capacitors, catalyst supports, and dry adhesives [1]. In addition to these direct applications, VA-CNT arrays are precursors for weaving CNTs into continuous sheets and fibers [2]. To synthesize millimeter-long VACNT arrays using chemical vapor deposition (CVD), a buffer layer of aluminum oxide (Al2O3) is often required to separate the supporting substrate and catalyst nanoparticles [3,4]. The aluminum oxide buffer suppresses the diffusion and aggregation of catalyst nanoparticles [5,6] and promotes the aromatization of carbon atoms during CNT growth [7]. The buffer is usually deposited on the substrate before catalyst deposition using physical techniques such as e-beam evaporation and thermal sputtering [4]. Buffer layers deposited using low-cost wet chemistry-based methods such as sol–gel, spin coating, dip coating, and layer-by-layer (LBL) assembly have only produced VA-CNT arrays with length up to several hundred micrometers [8,9]. To develop large-scale applications of VA-CNT arrays more than a millimeter in length, a wet chemistry-based method of buffer deposition is in need. In this letter, we report the growth of millimeter-long VA-CNT arrays on silicon chips coated with alumina buffer layers deposited using layer-by-layer (LBL) assembly of boehmite (c-AlOOH) nanoplates. This method involves four steps, including (1) immersion of a piece of silicon chip in polyethyleneimine (PEI) solution, (2) immersion of the chip in polyacrylic acid (PAA) solution, (3) immersion of the chip in boehmite suspension, and (4) annealing the chip at 0008-6223/$ see front matter 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.09.034 * Corresponding author: Fax: +1 574 631 9236. E-mail address: [email protected] (C. Na). C A R B O N 6 6 ( 2 0 1 4 ) 7 2 7 –7 2 9 Avai lab le a t www.sc ienced i rec t .com