Stable charge storage in granular thin films

Highly stable local charge storage by scanning probe microscopy methods has been observed in Fe-Si O2 (and Co-Si O2) granular thin films (5 nm metal granules embedded in Si O2) with decay times as much as two orders of magnitude longer than previously reported for heterogeneous films. Charge dissipation is well described as occurring in two regimes, a comparatively fast regime at short times (decay times of thousands of seconds) and a much slower regime at longer times (decay times of tens of thousands of seconds). Negative charging occurs more readily in these systems but positive charges are significantly more stable. Based on the results presented here, granular thin films have great potential as a new class of stable, tunable electrets suitable for nanoscale charge patterning and electrostatically directed assembly of complex nanostructures from discrete charged/polarized nanoparticles and macromolecules.