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. (C) 2002 Elsevier Science B.V. All rights reserved.