Atomistic process of electron-stimulated structural ordering in tetrahedral amorphous carbon

To have insight to the atomistic process of graphitic ordering in tetrahedral amorphous carbon films which is induced by irradiation of high-energy electrons, the role of temperature in the graphitization was experimentally studied. The change of electron diffraction patterns before and after irradiation at room temperature indicated graphitic ordering, but irradiation at - 170 degrees C resulted in disordering. Systematic measurements of the temporal evolution of electron energy loss spectra with irradiation at various elevated temperatures and data analysis based on the Johnson-Mehl-Avrami model yielded the activation energy for electron-stimulated ordering of as small as similar to 0.09 +/- 0.01 eV. The most plausible model to account for all the experimental facts is the dissociative diffusion that is triggered by the electron-stimulated displacement of carbon atoms at the initial sites. (C) 2007 Elsevier B.V. All rights reserved.