Structure-Dependent Feature of Electron Transport in Langmuir Multilayer Assemblies

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Abstract
The behavior of dc and ac conductivities is studied in the Langmuir multilayer films sandwiched between aluminium electrodes. The structure-dependence of conductivities has been systematically examined on different film structures constructed by the Molecular Assembly Technique. The constituent monolayers used were Cd salts of fatty acids CH3-(CH2)n-2-COOH with n = 16, 18, 20 and a mixture (C16)x-(C20)1–x. The structure dependent aspects are summarized in the following items, which are reasonably interpreted by the model based on the hopping or thermally assisted tunneling of electrons via localized states assumed at each monolayer interface: 1) exponential decrease of dc conductivity with increasing chain length of the fatty acid radical: 2) the same exponential variation of dc conductivity for mixed monolayers; 3) reduction of dc conductivity caused by one single C20 monolayer introduced into C16 multilayer system; 4) frequency-dispersion of conductivity in heterogeneous multilayer assemblies in accordance with the theoretical prediction.