ELECTRIC-FIELD MAPPING IN CONDUCTING LANGMUIR-BLODGETT FILMS

Scanning electron microscopy (SEM) performed on ultrathin in-plane conducting Langmuir-Blodgett (LB) films with a transverse electric field applied across the sample (voltage-induced contrast) shows electrically active defects selectively. Scratches or cracks which cut off conduction can be sorted out from others which do not, whereas standard SEM or optical microscopy does not distinguish between the two sorts of defects. Grain boundaries in LB conducting films of several semiamphiphilic compounds of tetracyanoquinodimethane (TCNQ) were easily observed, but were completely invisible by other methods. Grain boundaries are shown to be more resistive than the insides of grains, but the situation is shown to be less drastic than in thin films of conventional molecular conductors, owing to the alignment in molecular conducting planes in LB films.