STRUCTURAL-CHANGES AND ELECTRONIC-PROPERTIES OF GAMMA-IRRADIATED GRAPHITE - AN EXPERIMENTAL AND THEORETICAL-STUDY

In this article, we report the study of commercial carbon soots after being irradiated with a high dose of gamma rays. An industrial gamma b eam was used to irradiate the samples at 1 Mgy and a dose of 8.4 kGy/h r. Samples were examined in a high resolution electron microscope. Sev eral structures were observed but the two most important were onion la yers with fullerene like structure and graphitic like structure with r otational and traslational displacements. We present Extended Huckel c alculations showing that relative rotation of the carbon layers by 10 and 12 degrees basically have the same total energy as the unrotated s tructure. Therefore, rotation of the layers through those angles will be favored. At the same time, we calculate cohesive energy (E-coh), en ergy bands and projected density of states (PDOS) showing that as long as the rotation is induced, the system becomes metallic. At the same time, energy gaps are open in some bands, at certain points of the Bri llouin zone, a clear indication that a Peierls effect is present.