STRUCTURE AND ELECTRONIC-PROPERTIES OF AMORPHOUS-CARBON - FROM SEMIMETALLIC TO INSULATING BEHAVIOR

Correlations between the atomic-scale structure and electronic propert ies in amorphous carbon and its hydrogenated analogues are analyzed. T he metastable amorphous modifications with varying density 2.0-3.5 g/c m(3) and different amount of hydrogen have been generated by density-f unctional-based molecular dynamics applying different annealing regime s. The atomic-scale structure is characterized with special emphasis o n comparing neutron scattering with simulated diffraction data. The gl obal electronic band gap properties are related to the chemical bondin g and pi-cluster formation. While at low density the pi-pi gap closes owing to the large size of pi-clusters and the residual strain on the pi-system from the rigid bonding environment, the internal strain at high density of 3.0 g/cm(3) is maximally reduced by the separation of smaller pi-clusters. In the latter case, the pi-bonds optimally relax consistent with the opening of large pi-pi gaps up to 3 eV. While the internal strain again increases with further increase in the density, incorporation of hydrogen at 3.0 g/cm(3) additionally supports the re moval of internal strain by enforcing two-phase separation tendencies between chemically differently bonded carbon atoms.