MODEL STUDIES OF THE STRUCTURE AND CHEMICAL BONDING IN AMORPHOUS-CARBON FILMS PREPARED BY MAGNETRON SPUTTERING

The microstructure and chemical bonding properties of amorphous carbon with 2.0 g/cm(3) mass density prepared by magnetron sputtering have b een studied by electron diffraction measurements, molecular dynamics a nd Monte Carlo simulations. The model structures were generated by sim ulated annealing techniques applying both classical Tersoff and Keatin g potentials and a quantum mechanical density functional method. By co mparison of the experimental results with theoretically simulated diff raction data, the atomic scale structure is analyzed. The chemical bon ding properties of the models are evaluated within a local valence orb ital description. In this description, the electronic band gap propert ies are related to the formation of pi-bonded sp(2) clusters. Good agr eement is found between experimental and simulated diffraction data fo r models showing a minimum in their electronic density of states at th e Fermi energy. In these models, 60% of the atoms belong to one large pi-bonded cluster and, hence, form the matrix of the structures. Isola ted aromatic clusters of any size are not found. In the best fitting m odel, only 14% of all five-, six- and seven-membered rings are complet ely pi-bonded.