Atomic Displacements by Electron Irradiation in Pyrolytic Graphite

Abstract

The anisotropic threshold energy for atomic displacements and the displacement cascade process in electron-irradiated pyrolytic graphite are studied in the energy range from 0.12 to 1.0 MeV at three different temperatures by observing the a -axis electrical resistivity increases. The threshold energy T d is represented as \(T_{\text{d}}(\varPsi){=}A\cos^{2}\varPsi+B\sin^{2}\varPsi+C(1-\cos 4\varPsi){\equiv}(A,B,C)\) in eV, where \(\varPsi\) is the angle between the c -axis and the displacement direction. In the 6 and 80 K irradiations T d is given as a set of (23, 30, 0) and (31, 30, -2)±2 eV, and the cascade obeys the Harrison-Seitz Replacement model for \(\varTheta{=}0\)°, but obeys the Kinchin-Pease model for \(\varTheta{=}90\)°, where \(\varTheta\) is the angle between the c -axis and the electron direction. In the 285 K irradiations T d is either (28, 42, 0)±2 eV, or a set of (28, 42, 0) and (32, 42, -1)±2 eV, and the cascade obeys the Harrison-Seitz (no replacement) model for \(\varTheta{=}0\)°, 30°, 60° and 90°. The effects of crystal structure, lattice vibrations and thermal annealings are discussed using these results.