Disorder, clustering, and localization effects in amorphous carbon

The nanostructure of amorphous carbon thin films is described in terms of a disordered nanometer-sized conductive sp² phase embedded in an electrically insulating sp³ matrix. It is shown that the degree of clustering and disorder within the sp² phase plays a determining role in the electronic properties of these films. Clustering of the sp² phase is shown to be important in explaining several experimental results including the reduction of the electron spin resonance linewidth with increasing spin density and the dispersion associated with the width of the Raman active G band. The influence of structural disorder, associated with sp² clusters of similar size, and topological disorder, due to undistorted clusters of different sizes, on both spin density and Raman measurements, is discussed. An extension of this description to intercluster interactions to explain some of the electrical transport and electron field emission behavior is also presented.