Surface atomic properties of tetrahedral amorphous carbon

The surface energy and surface atomic structure of tetrahedral amorphous carbon has been calculated by an ab-initio method. The surface atoms are found to reconstruct into sp2 sites often bonded in graphitic rings. Placing the dangling bonds on adjacent surface atoms lower their energy by π-bonding and this is the source of the low surface energy. The even lower surface energy of hydrogenated amorphous carbon (a-C:H) is due to the hydrogenation of all broken surface bonds. © 2005 Elsevier B.V. All rights reserved.

Optical and electronic properties of amorphous diamond

The optical and electronic properties of highly tetrahedral amorphous diamond-like carbon (amorphous diamond, a-D) films were investigated. The structure of the films grown on silicon and glass substrates, under similar deposition conditions using a compact filtered cathodic vacuum arc system, are compared using electron energy loss spectroscopy (EELS). Results from hydrogenation of the films are also reported. The hydrogenated films show two prominent IR absorption peaks centered at 2920 and 2840 cm-1, which are assigned to the stretch mode of the C-H bond in the sp3 configuration on the C-H3 and C-H sites respectively. The high loss EELS spectra show no reduction in the high sp3 content in the hydrogenated films. UV and visible transmission spectra of a-D thin films are also presented. The optical band gap of 2.0-2.2 eV for the a-D films is found to be consistent with the electronic bandgap. The relationship between the intrinsic compressive stress in the films and the refractive index is also presented. The space charge limited current flow is analyzed and coupled with the optical absorption data to give an estimate of 1018 cm-3 eV-1 for the valence band edge density of states.