Macroscopic conductance in Langmuir–Blodgett bilayers of charge-transfer salts

Macroscopic conductance was observed in Langmuir–Blodgett (LB) bilayers deposited by two versions of the Langmuir–Schaefer (LS) technique. Bilayers of several compositions on the basis of donor compounds and donor–acceptor mixtures doped in ferric chloride solutions after the deposition were studied. Relatively high conductivity for such super-thin films was obtained due to the application of specific methods of substrate surface preparation and optimized procedure of doping. The conductivity values were in the range of 0.2–1.0 S cm−1 for bilayers and 10–30 S cm−1 for the films composed of 12 monolayers. This difference can be caused by the formation of bilayers of heterogeneous X-type/Y-type structure, which is in a good agreement with the results of surface potential measurements. Bilayers deposited by the LB technique either are non-conductive or possess very low conductivity. The most probable reason of such a behaviour is their discontinuity at the microscopic level. This conclusion is based on the data obtained by FT-IR spectroscopy, surface potential, and optical microscopy techniques as well as by transfer ratio measurements.