Electrical measurement on a phthalocyanine Langmuir-Blodgett film: II. Theeffect of the substrate surface treatment on the electrical characteristics

The stability and reproducibility of the electrical resistance measured on a thin Langmuir-Blodgett (LB) film of a copper tetraoctadecyl tetrapyridino [3,4-b:3',4'-g:3",4"-1:3''',4'''-q] porphyrazinium bromide (CuS18) were im proved with the control of the organic/inorganic interface between the film and the substrate. Homogenization of the physical surface properties both of the gold electrodes and of the glass substrate was obtained through graf ting self-assembled monolayers onto both types of surfaces. Such a strategy allowed fabrication of samples with reproducible resistance values due to a better quality of the LB transfer of the organic monolayer onto the subst rate. However, electrical drift with the elapsed time was still observed (a factor of 10(3) in 3 months). This ageing behaviour of the electrical resi stance appeared closely related to the instability of the gold clusters loc ated at the border of the electrodes. Their immobilization obtained with th e treatment of the substrate with a thiolsiloxane resulted in a much slower and reproducible electrical drift.