X-ray diraction characterization on the alignment degree of carbon nanotubes Anyuan Cao a, * , Cailu Xu a , Ji Liang a , Dehai Wu a , Bingqing Wei b a Department of Mechanical Engineering, State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China b Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA Received 1 May 2001 Abstract X-ray diraction XRD) studies were performed on carbon nanotubes CNTs) with various alignment degrees synthesized by catalytic pyrolysis of ferrocene and xylene. A qualitative relationship between the peak intensities of the XRD patterns and the degrees of nanotube alignments was established. The intensity of the 0 0 2) peak decreases monotonically with higher nanotube alignment. This method provides a simple way to characterize the alignment degree of as-grown large-area CNTs. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Since the bulk production of carbon nanotubes CNTs) [1,2], extensive work has been carried out in order to align these one-dimensional 1D) nanostructures [3±5]. It is dicult to arrange CNTs into a desirable regular group because of their very high aspect ratios [6]. Direct growth of large-area, self-oriented CNTs [7] provides the opportunity for further studying regular CNT ar- rays macroscopically. As the aligned CNTs grow vertically on the substrate with their tips pointing upward uniformly, many new properties may be expected for them comparing to disorder ones. Patterned CNT arrays exhibited good ®eld emis- sion properties [8] and could act directly as cold cathodes for ¯at panel displays FPD). A higher capacity in hydrogen storage of dense-aligned CNTs than disorder ones was obtained due to the presence of micro inter-tube spacing [9]. Vertically aligned CNT ®lms have also shown an ultra-high absorption of solar energy, which could be used as eective solar thermal collectors [10]. However, full investigation of the bulk aniso- tropic properties of CNTs has been hindered by the lack of a controllable way for producing aligned CNTs. As-grown CNTs synthesized by arc-discharge and chemical vapor deposition show various alignment degrees, for example, nanotubes grown on Au ®lms are less aligned comparing to those grown on quartz substrate [11]. Also, their alignment degree is sensitive to many growth conditions, such as temperature, carbon source and its ¯owing rate. A small ¯uctuation of such a condition may lower their alignment considerably. Therefore an eective way to characterize the nanotube alignment is necessary for practical ap- plications of them. www.elsevier.com/locate/cplett 17 August 2001 Chemical Physics Letters 344 2001) 13±17 * Corresponding author. E-mail address: cayuan96@mails.tsinghua.edu.cn A. Cao). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00671-6