Fabrication and characterization of charge-transfer complex films by a bias-voltage LB technique

Abstract

We have investigated the effect of bias voltage applied to an electrically conductive substrate on the formation of adsorption Langmuir–Blodgett (LB) films. In fabricating the adsorption LB films, we used tetracyanoquinodimethane (TCNQ) with a long alkyl chain as a molecule for spreading monolayers on the subphase and tetramethyl- p-phenylenediamine (TMPD) as a material for adsorbing from the subphase to the monolayers. It is well known that TCNQ and TMPD are acceptor-like and donor-like molecules, respectively. In the visible absorption spectra and Fourier transform infrared reflection–absorption spectra of the adsorption LB films fabricated under several bias conditions, the peaks assigned to TCNQ show a clear dependence on the bias voltage. The electrical conductivity corresponding to the quantity of charge-transfer complex was also obtained. These results demonstrate that the bias-voltage LB technique enables us to control the formation of the charge-transfer complex.