Recently, highly-ordered alternate structures have been expected to bring out different properties from those of uniform films 1, 2. Organic ultrathin multilayerd films using self-assembly and spin-coating method, where the alternate spontaneous adsorption based on self-assembling processes proceeds during the spin-coating, are promising candidates to fabricate those structures.
Copper phthalocyanine (CuPc) tetra sulfonic acid, tetrasodium salt (CuPcSAS) and polyaniline (PA) have been chosen as functional organic materials to adsorb on the other alternately. The structure consisting of alternate ultrathin films promises new properties, since CuPc has been known as a p-type organic semiconductor and PA as a conductive polymer in the acid-doped state. The self-assembling mechanism is based on the electrostatic interaction between negatively charged CuPcSAS and positively charged PA. Besides, they did not dissolve in the other solvent, because CuPcSAS is hydrophilic and PA is hydrophobic. These are important properties for this method.
In the spontaneous adsorbing process, it is important to know each saturation property of adsorption. UV-Vis absorption was, therefore, measured to estimate the amount of adsorbed molecules against elapsed time, and then saturation properties were confirmed. Other important factors, the thickness and the flatness of each layer, were also evaluated with atomic force microscopy (AFM). The thickness of each layer was comparable to the mono-molecular layer and the surface was flat enough. These results strongly suggest that the alternate ultrathin films can be fabricated as initially expected. The electrical properties of fabricated films were evaluated using the four-probe method and the field effect transistor measurements. The properties associated with the film structure and molecular species were compared.
Dan Li, Yadong Jiang, Zhiming Wu, Xiangdong Chen and Yanrong Li: Thin Solid Films 360(2000)24.
Department of Electronics and Mechanical Engineering, Chiba University
1-33 Yayoi-cho, Inage-ku Chiba-City, Chiba 263-8522 JAPAN