Kinetic roughening of charge spreading in a two-dimensional silicon nanocrystal network detected by electrostatic force microscopy

The charging dynamics of silicon nanocrystals embedded in a silicon-dioxide matrix is studied using electrostatic force microscopy. Varying the average oxygen content of the silicon-rich-oxide samples, different charge-spreading behaviors are observed. Three kinds of behavior are distinguished: charge confinement in isolated clusters (insulating), spreading via a network of clusters and metallic. They relate to the local material composition with a threshold silicon/silicon oxide ratio for conduction, a characteristic of percolation. Close to this threshold, in situ and real-time experimental charge spreading on the timescale of several hours in a two-dimensional silicon nanocrystal network is evidenced, with an irreversible evolution of a rough borderline of the electron cloud.