Two-step transfer of conducting Langmuir films from a glycerol subphase

Abstract

A new method for building up conducting Langmuir-Blodgett (LB) films is described. The film is initially formed and compressed on a glycerol subphase from a semi-amphiphilic mixed-valence conducting tetracyanoquinodimethane (TCNQ) salt, namely octadecylpyridinium + ∮(TCNQ1,45) −. We show that the conducting properties are retained on this subphase for surface pressures up to 18 mN m −1, which corresponds to the elasticity limit of the film. The film is then shifted onto a water subphase, contained in a dipping compartment, which has been previously incorporated in the main Langmuir trough, the water level being set identical to that of the glycerol. The shift onto the water allows the transfer onto a solid substrate with the classical dipping-withdrawing method. The propertie films are investigated by analysing their UV-visible and IR spectra and their linear dichroism. The IR and UV-visible spectra are reminiscent of those of mixed-valence TCNQ complexes with only a poor conductivity. This behaviour is verified bya d.c. conductivity measurement at room temperature, which provides a stable value of 10 −4μ −1 cm −1. Furthermore, the high degree of order in the film is evidenced by its strong dichroic behaviour. It turns out that TCNQ molecules stand edge on with their molecular planes roughly perpendicular to the plane of the substrate and their long axis close to being perpendicular to it. In addition, the influence of the subphase in the fibrication of LB conducting films is pointed out.