Improvement of Carbon Nanotube Films on SiC formed by Surface Decomposition by Hydrogen Peroxide Purification
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Improvement of Carbon Nanotube Films on SiC formed by Surface Decomposition by Hydrogen Peroxide Purification Takahiro Maruyama, Fumiya Nakahama, Shigeya Naritsuka Department of Materials Science and Engineering, Meijo University, Tempaku, Nagoya 4688502, JAPAN
ABSTRACT We studied the effects of annealing in H2O2 on the morphologies and structures of “as grown” high-density, well-aligned multi-walled carbon nanotube (MWNT) films formed by surface decomposition of SiC. After annealing in H2O2 solution at 100ºC for 3 h, the G/D ratio increased from 1.44 to 2.33, the FWHM of the G band peak became narrower, and a D' shoulder peak appeared. Transmission electron microscopy (TEM) revealed that the dispersion of MWNTs in dimethylformamide (DMF) solution was improved, suggesting that film impurities were reduced and that damage to the MWNTs was negligible. After annealing for 9 h, the G/D ratio decreased to 1.57, and exfoliation of some MWNTs was observed. In addition, several functional groups such as carboxylic (-COOH) and hydroxyl (-OH) were formed on the surface of the MWNTs. From these results, we conclude that annealing in H2O2 under proper conditions can effectively purify “as grown” MWNT films formed by surface decomposition of SiC. INTRODUCTION Carbon nanotube (CNT) growth by surface decomposition of SiC is a unique growth technique. By this method, high-density, well-aligned multi-walled CNT (MWNT) films can be formed on 6H-SiC(000-1) wafers without a metallic catalyst [1], and their chirality is restricted to a zigzag-type structure [2]. In addition, the grown CNTs are atomically connected to SiC crystals at the interface, which is useful for fabricating CNT devices [2]. We previously investigated the mechanism of MWNT growth by this method [3, 4], and reported a means of improving the homogeneity of the CNT diameter [5]. Despite these advantages, Raman measurements indicated that the D band intensity was comparable to the G band intensity, suggesting that the quality of CNT films was poor [6]. Furthermore, transmission electron microscopy (TEM) indicated the inclusion of carbon-related impurities among the CNTs [7]. In this work, we attempted to purify “as grown” MWNT films formed by SiC surface decomposition by annealing them in H2O2 solution. In order to utilize their unique structures for practical application, it is essential to improve the quality of MWNT films without separation from SiC substrates (“as grown” MWNT films). To accomplish this, purification by H2O2 treatment, a relatively mild oxidant [8, 9], is expected to be effective. This is because most of the impurities in the MWNT films are carbon-related materials, and the mild oxidation treatment would be useful. However, purification treatments for “as grown” MWNT films by surface decomposition of SiC have not been reported yet. Our results showed that H2O2 treatments under optimum conditions are effective to improve the quality of “as grown” MWNT films on SiC.
EXPERIMETAL DETAILS The MWNT films used were synthesized by the SiC sur
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