Charge transport in a liquid crystalline triphenylene polymer monolayer at air–solid interface

Abstract

We have prepared a monolayer of a novel liquid crystalline polymer derived from 2,6-dihydroxy-3,7,10,11-tetraalkoxy-triphenylene (PHAT) at an air–water interface and transferred it onto freshly cleaved mica as well as gold coated mica substrates by the Langmuir–Blodgett (L–B) technique. The atomic force microscope (AFM) images of these L–B films show a uniform coverage with a thickness of 1.5 nm. Electrical conductivity measurements were carried out on the PHAT monolayer deposited on the gold coated mica substrate using a current sensing AFM (CSAFM). The gold substrate–PHAT monolayer–cantilever tip of CSAFM forms a metal–insulator–metal (M–I–M) junction. The CSAFM yields a non-linear current–voltage (I–V) curve for the M–I–M junction. The analysis of the I–V characteristics of the M–I–M junction indicated that the charge transport in the liquid crystalline polymer monolayer is by the direct tunneling mechanism. The barrier height for the PHAT monolayer was estimated to be 1.22 ± 0.02 eV.