DECAY OF SURFACE-CHARGE ON NORMAL-OCTADECANE CRYSTALS

Charge is deposited either on a free surface of a crystal sample from a corona discharge or else by contact on to an evaporated aluminium electrode on the surface. A high-resolution induction probe with a computer store is used to monitor the behaviour of charge on the surface. Charge deposited on the free surface decays away into the bulk with a mobility in the range 10-13 to 10-15 m2 V-1 s-1. On the other hand, an aluminium electrode forms a blocking contact and apparent charge decay then occurs only by dielectric polarisation of the bulk. There is also evidence that charge can spread from the edge of the evaporated electrode on to the surrounding free surface of the crystal. Of most significance is the demonstration that the method permits clear detection of conductive channels in the octadecane crystals.