Local Charge Storage in Thin Silicon Oxide Films: Mechanisms and Possible Applications

We report on charge storage in silicon oxide below the micrometer scale as needed for the controlled attachment of charged particles. Thin silicon oxide films were locally charged using conductive atomic force microscopy. The charge was investigated using Kelvin probe force microscopy. We found that charges are stored in different traps in the silicon oxide matrix. We also discovered two different decay pathways: one parallel and one perpendicular to the surface. The parallel path, which is mediated by water adsorbed on the surface, was suppressed by a hydrophobic monolayer. This led to a stabilization of the stored charges in the oxide, which enabled the targeted attachment of ionic species from solution. As proof of concept, we deposited dye molecules selectively to previously written charge patterns on silicon oxide for the first time.