On the charge storage and decay mechanism in silicon dioxide electrets

A mechanism for both the storage and the decay of charge in a charged silicon dioxide layer is proposed. The oxide layer needs neutral electron traps to obtain stable trapped negative charge, after having been charged, resulting in an electret that can be applied in microphones. The deprotonization of the silanol groups, followed by charge injection, results in an electrochemical reaction with immobile SiO^- as one of the reaction products. Decay of the stable charge thus obtained can occur by the clustering of water molecules at inner silanol groups, resulting in a conductive hydrogen bonded network, which eventually leads to the discharge of the electret. Measurement results are presented, showing a considerable decrease in surface conductivity, after having grafted the SiO₂ surface, resulting in covalently bonded, relatively long octadecyl silane chains