Electronic and optical properties of amorphous carbon with different sp3/sp2 hybridization ratio

Abstract

To study the electronic and optical effects of amorphous carbon (a-C) films with different sp3/sp2 hybridization ratio, five amorphous carbon models with gradient changes of density are established. Work function, band structure, dielectric function, complex refractive index, absorption coefficient, reflectivity and loss function have been calculated and analyzed based on first principles. The results show that sp3/sp2 hybridization ratio raises, formation energy and work function are reduced when the density increases. Meanwhile, band structure distribution of the a-C film at density of 3.5 g/cm3 has similarities with that of the diamond in highly symmetric points. In addition, the optical properties of the a-C film are significantly improved as the sp3-C content increases. Particularly, the peak of the absorption coefficient become higher, the half-peak width enlarges and the reflectivity is also reduced obviously, indicating that the a-C films with the larger sp3/sp2 hybridization ratio do increase the quantum efficiency of photocathodes to a certain extent. Therefore, this work can further guide the preparation experiment of a-C film, which has a great worth to improve the optoelectronic performance of electron emission devices.