Determination of the contribution from the substrate/film interface to the surface potential of LB films

The various contributions to the surface potentials of Langmuir-Blodgett (LB) films were probed by depositing Y-type multilayers of cadmium stearate (CdSt) onto gold-coated glass substrates with different numbers of odd and even layers. For multilayers with even numbers of layers, the saturation potential was ca. -150 mV, which is attributed to charge injection from the substrate, since the molecular dipoles are cancelled. For LB films with odd numbers of layers, saturation occurs at ca. +180 mV, as a result from the dipolar contribution in addition to the component from charge injection. Moreover, the double-layer potential observed in CdSt Langmuir monolayers, of ca. -260 mV, is replaced by a contribution of only -50 mV upon transfer onto the substrate.