Nano-Cylinder Structure Studied by X-ray Diffraction
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Nano-Cylinder Structure Studied by X-ray Diffraction
Gu Xu, Zhechuan Feng,1 Zoran Popovic,2 Jianyi Lin3 and Jagadese.J. Vittal4 Department of Materials Sci. & Eng., McMaster University, Hamilton, L8S 4L7, Canada 1
Axcel Photonics Inc., 45 Bartlett Street, Marlborough, Massachusetts, 01752
2
Xerox Research Center of Canada, Mississauga, Ontario, L5K 2L1, Canada 3 Department of Physics, National University of Singapore, 119260, Singapore 4 Department of Chemistry, National University of Singapore, 119260, Singapore ABSTRACT The study of nano-cylinder structure has attracted much attention due to the application of multi-wall carbon nanotubes (MWCNTs). While some TEM observations indicate that they are formed by seamless concentric cylinders, other TEM and high pressure X-ray diffraction studies suggest that they look like scrolls of graphite sheets. Although many people now accept the concentric cylinder model, there has been no confirmation reported. On the other hand, this structural difference of MWCNTs plays a crucial role in determining the properties and suitability for future applications. For example, the periodical boundary condition can only be imposed for cylinders, but not for scrolls. To resolve this issue, we employed high-resolution X-ray diffraction to measure detailed profiles of the Bragg peaks for high-purity MWCNTs. We then identified some unusual observations unique to the nano-cylinder structure, followed by the analysis of the structural difference in the Fourier transform between nanotubes formed by scrolls and concentric cylinders. The simulation results are then compared with the experimental data to reveal the structural details.
INTRODUCTION The determination of nano-sized structures has been a great challenge to materials scientists and engineers. As a recent example, the cylindrical nature of multi-wall carbon nanotubes (MWCNT) has been much debatable [111]. While most of the transmission electron microscopy (TEM) observations indicate that they are formed by seamless concentric cylinders [1,2], some TEM and high-pressure X-ray diffraction studies suggest that they look like scrolls of graphite sheets [10,11]. This structural difference of MWCNT plays a crucial role in determining the properties and suitability for future applications, because, e.g., the periodical boundary condition can only be imposed for cylinders, but not for scrolls [12,13]. Although many people accept the concentric cylinder model, there has been no confirmation reported. To resolve this issue, we present high resolution x-ray diffraction results of high purity MWCNT made by catalytic decomposition, where non-equal Bragg peak breaths and shifting of the peak positions were observed. We then identify some unusual observations unique to the nano-cylinder structure, followed by the analysis of the structural difference in the Fourier transform between nanotubes formed by scrolls and concentric cylinders. The simulation results are then compared with the experimental data to reveal the structural details.
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