Persistent microscopic charge patterns in amorphous silicon thin films for guided assembly of colloids

Persistent microscopic charge patterns are written on hydrogenated amorphous silicon thin films (a-Si:H) using ambient atomic force microscopy (AFM). The stored charge is characterized as a function of time by Kelvin force microscopy. Negatively charged patterns are prepared using positive voltage pulses on AFM tips. The resulting surface potential difference as high as 0.8 V is not influenced by exposure to pure water. Using negative tip voltages positively charged patterns are grown on the a-Si:H surfaces via anodic oxidation. After exposure to water the positive potential contrast is enhanced by >100%. The origin of potential contrast before and after water exposure is discussed. This technology can open interesting prospects for hybrid organic-silicon devices.