Slow relaxation of polar impurities in amorphous carbon thin films through capacitive spectroscopy

The dielectric properties of wide and small gap amorphous carbon thin films were probed through capacitive spectroscopy measurements. We report a long time evolution, ranging between a few hours and a few days, of the capacitive response of the films. The reported behavior suggests very different hypotheses, such as facilitated diffusion of polar impurities in porous films, or as slowly relaxing electronic states lying at the substrate/film interface and built-in stress relaxation. In the case of a contamination by polar impurities adsorbed on the voids surface, we develop a model predicting the correction to the capacitive response due to the contamination as a function of the density of impurities and their dynamical properties.