The structure and electrical properties of highly polar indandione-1,3 pyridinium betaine (IPB) derivatives have been studied in vacuum-evaporated thin films and Langmuir-Blodgett (LB) multilayer assemblies. Phase transitions induced by temperature and/or electric field have been observed in LB films of an amphiphilic derivative of IPB. The LB films of IPB, obtained at room temperature, form a Y-like structure which melts at about 50 degrees C to produce spherical domains, having Z-like structure, which remain stable up to 110 degrees C. Similar phase transitions can be induced by an electric field with epsilon greater than or equal to 2X10(5)V cm(-1) at room temperature. In the new Z-like phase of the IPB LB films, the electrical conductivity increases by some five or six orders of magnitude and the activation energy of dark conductivity decreases from 0.18+/-0.03 eV to practically zero. The vacuum-evaporated IPB films yield low electrical conductivity (sigma=10(-15)-10(-16) S cm(-1)), whereas in the LB multilayers a notable anisotropy of conductivity is observed. In case of coplanar cells the conductivity increases to sigma=10(-8) S cm(-1). In sandwich-type LB samples the conductivity value is similar to that of the vacuum-evaporated polycrystalline thin films.
Structural and electrical characterisation of betaine-type, organic, molecular, thin evaporated films and LB multilayers
CIUCHI F;
1997
Abstract
The structure and electrical properties of highly polar indandione-1,3 pyridinium betaine (IPB) derivatives have been studied in vacuum-evaporated thin films and Langmuir-Blodgett (LB) multilayer assemblies. Phase transitions induced by temperature and/or electric field have been observed in LB films of an amphiphilic derivative of IPB. The LB films of IPB, obtained at room temperature, form a Y-like structure which melts at about 50 degrees C to produce spherical domains, having Z-like structure, which remain stable up to 110 degrees C. Similar phase transitions can be induced by an electric field with epsilon greater than or equal to 2X10(5)V cm(-1) at room temperature. In the new Z-like phase of the IPB LB films, the electrical conductivity increases by some five or six orders of magnitude and the activation energy of dark conductivity decreases from 0.18+/-0.03 eV to practically zero. The vacuum-evaporated IPB films yield low electrical conductivity (sigma=10(-15)-10(-16) S cm(-1)), whereas in the LB multilayers a notable anisotropy of conductivity is observed. In case of coplanar cells the conductivity increases to sigma=10(-8) S cm(-1). In sandwich-type LB samples the conductivity value is similar to that of the vacuum-evaporated polycrystalline thin films.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
