Enhanced current in nematic liquid crystal cell using alkanethiol self-assembled monolayer

Photoinduced carrier injection through the aligning layer-liquid crystal (LC) interface or the electrode-LC interface has been suggested as the fundamental process involved in the surface mediated photorefractive effect in the LC cell. In this paper we construct LC cells with the gold film as one substrate as well as cells with the gold film covered with decanethiol and hexadecanethiol self-assembled monolayers (SAMs). We find that the current-voltage curves for the three kinds of cells are consistent with the equations describing carrier injection and bulk-ion-generation. The dark current and photocurrent are enhanced by the existence of alkanethiol SAM. The length of the alkane chain of alkanethiol SAM also affects the currents. The above experimental results indicate that the model which involves carrier injection from the gold electrode to the LC is more suitable and the role of the alkanethiol aligning layer is to enhance carrier injection.