Evolution kinetics of sp2 ordering in tetrahedral amorphous carbon films induced by electron irradiation

The kinetics of sp3 to sp2 structural conversion in tetrahedral amorphous carbon (ta-C) films induced by sample irradiation with an electron beam of transmission electron microscope was studied by systematically measuring the temporal evolution of the graphitic phase detected by electron energy loss spectroscopy (EELS). The results analyzed in the framework of the Johnson-Mehl-Avrami model indicates that the phase front velocity increases in proportion to the irradiation beam current density, providing an experimental support for the notion that the effect is caused by an electronic excitation effect. It was inferred from the experimentally assessed kinetic order index that the three-dimensional growth of graphitic phases is enhanced by electronic excitations. Possible microscopic mechanisms are discussed.