Surface morphology and current–voltage characteristics of monolayer Langmuir–Blodgett films of conjugated organic molecules

The surface morphology of UV-light polymerized monolayer Langmuir–Blodgett films of 10-12 pentacosadyinoic acid (12-8 diacetylene) deposited on flat gold substrates was imaged by atomic force microscopy. Current–voltage characteristics of the monolayer film was measured by using the tip of a scanning tunneling microscope at individual points on the film surface and compared to the ones measured on the bare gold substrate. The measured current–voltage characteristics are correlated and discussed with the expectation of the Au Fermi level of the substrate, Pt/Ir Fermi level of the tip and the higher occupied molecular orbital/lower unoccupied molecular orbital energy levels of the polydiacetylene molecule.