A Structural Analysis Method for Graphite Intercalation Compounds
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A Structural Analysis Method for Graphite Intercalation Compounds Tatsuo Nakazawa, Kyoichi Oshida, Takashi Miyazaki, Morinobu Endo1 and Mildred S. Dresselhaus2 Nagano National College of Technology, 716 Tokuma , Nagano-shi, 381-8550, JAPAN 1 Shinshu University, 4-17-1 Wakasato, Nagano-shi, 380-8553, JAPAN 2 Currently on leave from the Massachusetts Institute of Technology, Cambridge, MA 02139, USA ABSTRACT Study of the microstructure of electronic materials can be enhanced by using high resolution transmission electron microscopy (TEM) combined with the technique of digitized image analysis. We show here a practical image analysis method for the microstructures of acceptor graphite intercalation compounds (GICs) with CuCl2 and FeCl3 intercalates. The two dimensional fast Fourier transform (2D-FFT) was used for the frequency analysis of the TEM pictures. It is found that the lattice images of CuCl2-GICs consist of different frequency images corresponding to specific frequencies. The detailed features of the stage-1 structure of the FeCl3-GICs is extracted quantitatively by this method from a relatively indistinct TEM picture. The stage structure of the CuCl2- and FeCl3-GICs are further investigated by analyzing the reconstruction of the TEM images by means of the two dimensional inverse FFT (2D-IFFT). INTRODUCTION Well-staged acceptor graphite intercalation compounds (GICs) exhibit many useful electrical properties, such as a large magnitude of the conductivity with a metallic temperature-dependence. The electrical and mechanical properties of GICs are thought to strongly depend on the GIC staging structure. In order to analyze the micro-structure of materials, transmission electron microscope (TEM) observations provide one of the most useful techniques, because TEM images give very detailed information about the nature of the lattice structure and the anomalies found in a very small sample. In this study, the method of high-resolution TEM observations combined with digitized image analysis is used to get a more quantitative evaluation of the staging structure in GICs. Analysis of the microstructure of GICs is largely enhanced by using this technique. The GICs can be synthesized in the fiber matrix of vapor grown carbon fibers (VGCFs) [1,2] that consist of a honeycomb network of concentrically stacked cylindrical layers of graphene planes around the fiber axis. While TEM observations of well-staged acceptor GICs with CuCl2 and FeCl3 intercalates have revealed the staging structure of the GICs, these observations have not yielded much quantitative information. Digitized image analysis is applied here to promote the quantitative interpretation of the TEM images and to clarify the structure of GICs. TEM images of CuCl2 and FeCl3 GICs are evaluated by means of the image analysis method described here using a 2-dimensional (2D) fast Fourier transform (FFT). EXPERIMENTAL DETAILS Sample preparation The preparation of intercalated VGCF samples in brief is as follows [3]. The precursor VGCF was obtained by the thermal decompo
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