Two-Dimensional Ordering of Ion Damaged Graphite
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WO-DIMENSIONAL ORDERING OF ION DAMAGED GRAPHITE S. DRESSELH 4 US,*0# G. BRAUNS 1 EIN,@ G. DRESSFLHAUS, + B.S. ELMAN,*0 AND J.M. GIBSON B. WILKENS, T. VENKATESAN Center for Materials Science and Engineering; 'Department of Physics; #Department of Electrical Engineering and Computer Science; +Francis Bitter National Magnet L boratory; Massachusetts Institute of Technology, Cambridge, MA 02139; Bell Laboratories, Murray Hill, NJ 07974, USA
ABSTRACT Post implantation annealing of ion-damaged, highly oriented pyrolytic graphite (HOPG) has been studied by Raman spectroscopy, the ion channeling technique and Transmission Electron Microscopy. Complementary information obtained by these methods provides confirmation for the completion of the first step of graphitization of iondamaged graphite at annealing temperatures of -23000 C. This is manifested by the formation of carbon planes with two dimensional ordering but no correlation in the third (c-axis) dimension.
INTRODUCTION Radiation damage introduced into graphite during the process of ion implantation can be removed by subsequent annealing and recrystallization (graphitization) of the damaged region. Bulk graphitization of different types of carbons has been widely studied [1]. The graphitization is generally considered to be a two step process. The first step involves in0 plane ordering which starts above 1500 C. This is followed by the second 0 step of graphitization above 2000 C, where, in addition, three dimensional ordering takes place [1]. Generally, x-ray diffraction experiments are performed to measure the interplanar distance from the linewidth of the (002) reflection, from which the degree of graphitization is determined. Diamagnetic susceptibility measurements of the magnitude of f and the anisotropy f3 - '1 are also carried out to monitor the graphitization process as a function of heat treatment temperature [1]. Raman spectroscopy was successfully applied to follow annealing experiments on ion implanted BOPG [2,3] and the heat treatment of graphite fibers prepared by the pyrolysis of benzene [4]. The technique is sensitive to disorder in the crystalline substrate, since for disordered materials Raman scattering is not limited to contributions from Ramanactive zone-center modes, and contributions from other phonons in the Brillouin zone become possible. The first-order Raman spectra are highly sensitive to the first step of graphitization, while the onset of the second step of graphitization can be determined from the second-order Raman spectra [2,3,5]. For most carbon blacks, the heat treatment temperature for the onset of the second step of graphitization is found to 0 0 be between 2300 C and 2500°C; for cokes it is -2000 C [1]. Rutherford backscattering spectrometry (RBS) in the channeling geometry is widely applied to obtain information on lattice disorder and recrystallization of ion-damaged semiconductors [6-8] and to HOPG [9]. In the present work we demonstrate how the complementary information from Raman scattering and RBS measurements can be suppl
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