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M. Endo Department of Electrical Engineering, Faculty of Engineering, Shinshu University, Nagano 380, Japan

T. Nakajima Division of Molecular Engineering, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto 606, Japan

S. L. di Vittorio Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

M. S. Dresselhaus Department of Physics and Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

G. Dresselhaus Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 9 March 1992; accepted 23 October 1992)

A digitization of the TEM pictures of fluorine-intercalated graphite fibers has been used to carry out quantitative measurements of the defect structure of this material. Emphasis is given to both the computer analysis technique and to the characterization of the defects. The amount of intercalation-induced disorder increases with increasing fluorine concentration. The fast Fourier transform of the digitized TEM image exhibits two diffuse spots, corresponding to the c-axis repeat distance of the intercalation compound. The length and width of the spots are a measure of the out-of-plane and in-plane disorder present in the fibers. From the fast Fourier transform, the distribution of interlayer repeat distances and the fraction of unintercalated graphite regions throughout the material is obtained. By selecting a small range of repeat distances and carrying out an inverse fast Fourier transform, the spatial distribution of material with a given repeat distance is determined. Regions with the same repeat distance are found to form islands. This particular feature of fluorine graphite intercalation compounds, as well as the nature of the microscopic defects and the staging behavior of fluorine-intercalated graphite fibers, are discussed in connection with the dual covalent and ionic nature of the carbon-fluorine bond in fluorine-intercalated graphite.

I. INTRODUCTION Many characterization techniques are used to measure quantitatively the amount of disorder present in a material. Among the most widely used in the field of carbon-based materials are transport, Raman scattering, and x-ray diffraction.1-2 By measuring such parameters as the resistivity and its temperature dependence, the magnitude and size of the magnetoresistance, and the magnitude of the disorder-induced peak in the Raman spectrum, it is possible to obtain a reliable numerical estimate of the magnitude of the disorder in the fibers (specified by the sheet resistance RD, the Raman linewidth, and crystallite sizes in the a and c directions 512 http://journals.cambridge.org

J. Mater. Res., Vol. 8, No. 3, Mar 1993 Downloaded: 08 Apr 2015

La and Lc). However, these techniques do not provide much information on the specific nature of the disorder present in the material. Furthermore, such measurements yield information about the disorder, averaged over t