Image analysis of TEM pictures of fluorine-intercalated graphite fibers

Abstract

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.

A model for disorder in fluorine-intercalated graphite

“…4 The width of the I c value distribution increases as the fluorine concentration increases. The C x ¥ GIC's are found to exhibit good staging behavior for stage I to stage IV samples (no C X F samples of higher stage have been experimentally synthesized).…”

“…4 In addition to this waviness, the fluorine GIC's are inhomogeneous, 4 forming islands about 70 A in diameter, with varying interlayer repeat distances I c , corresponding to varying fluorine concentrations. No substantial nonintercalated (where a a and a c are the in-plane and out-of-plane conductivities, respectively) remains extremely high.…”

“…Transport measurements, 1 " 3 transmission electron microscopy (TEM), 4 electron spin resonance (ESR), 5 and optical 6 measurements have established the presence of disorder in fluorine graphite intercalation compounds (GIC's) and have helped characterize the nature of this disorder, both structurally and electronically. It is now clear that the properties and structure of fluorine GIC's are quite different from that of most other known GIC's.…”

“…In contrast, this planarity of the carbon planes does not persist after intercalation of fluorine, and TEM micrographs show that the carbon planes in fluorine GIC's are buckled. 4 The unique electronic and structural properties of fluorine GIC's are especially striking when compared to other halogen GIC's, which have a similar chemical structure. The purpose of this paper is thus to explain the differences between fluorine GIC's and other GIC's, with special reference to halogen GIC's.…”

Structural analysis of carbon nanofiber by transmission electron microscopy and image processing

“…In this report, a partial structure of the nano®bers produced by the vapor growth method was investigated by high resolution transmission electron microscopy (HRTEM) combined with image processing [5,6].…”