Influence of growth temperature on the structure, composition and bonding character of nitrogen-doped multiwalled carbon
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jun Pan School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian, Liaoning 116024, People’s Republic of China
Bin Wen, Xiaoyang Song, Chenguang Liu and Tingju Lia) School of Materials Science and Engineering, Dalian University of Technology, Dalian, Liaoning 116024, People’s Republic of China (Received 25 July 2010; accepted 12 October 2010)
Nitrogen-doped multiwalled carbon nanotubes (N-doped MWNTs) were synthesized in a large quantity by the pyrolysis of pyridine at various temperatures in the range of 750–950 °C. The influence of temperature on the morphology, composition, thermal stability, and bonding nature of N-doped MWNTs was investigated. It is found that the yield of N-doped MWNTs increases linearly with the increase of the growth temperature. The maximum N content (4.6 at%) in MWNTs was obtained from a sample grown at 900 °C. N-doped MWNTs synthesized at 950 °C possess a unique drumlike morphology with the highest oxidizing temperature (535 °C). It is evidenced that N atoms are incorporated into the graphitic network in three different bonding forms and their relative content is affected by the growth temperature, which shows a clear influence on the morphology of N-doped MWNTs.
I. INTRODUCTION
Carbon nanotubes (CNTs), the new members of carbon isomers, were discovered in the soot of the arc-discharge method by Iijima in 1991.1 Their unique quasi-onedimensional geometry structures have attracted considerable attention in research for electronic and optical applications.2,3 However, CNTs show a variety of electronic behaviors from metallic to semiconducting, depending on the tube diameter and the chirality.4–7 Controlling these parameters during synthesis is still a challenge for current research, which seriously restricts the future applications of CNTs. Doping CNTs with other chemical elements (B or N) provides an effective way to solve this problem.8,9 Theoretical calculations have demonstrated that substitutional N doping into CNTs gives rise to metallic behaviors, because N atoms provide additional free electrons for the conduction band.10,11 Such nanotubes exhibit the advantage that their electronic properties mainly depend on composition and are relatively easy to control. N-doped MWNTs have been studied extensively.12–17 Sen et al. first synthesized N-doped MWNTs by the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.58 J. Mater. Res., Vol. 26, No. 3, Feb 14, 2011
pyrolysis of aza-aromatics over Co nanoparticles in an Ar atmosphere in 1997.18 The current-voltage curve of asgrown N-doped MWNTs obtained from UHV-STM studies shows a conductance of 1.2 nA/V, which is higher than that of the undoped MWNTs.10 Suenaga et al. successfully synthesized N-doped MWNTs by the direct current magnetron sputtering method in 1999.19 These nanotubes were grown in a highly packed perpendicular form on a sodium chloride substrate. Maldonado et al. prepared N-doped MWNTs with a range of N content from 0 to 10 at% by a floating catalyst chemi
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