Optical and Electrical Properties of Merocyanine Dye LB Films by Various Time of UV Irradiation and Heat Treatment

Abstract

The Langmuir-Blodgett (LB) technique provides many possibilities for the control of film thickness, dimensions, and molecular structures on the nanometer scale. Various kinds of dye molecules have been found to form the J-aggregation which has been used as sensitizers of silver halide photography for long time. In recent years, they attract attention as model systems for investigating the ultra-fast exciton dynamics, materials for ultra-fast nonlinear optical devices, fluorescence probes for mitochondrial membranes. We fabricated the merocyanine dye LB films with arachidic acid (AA). In order to observe the J-aggregation of the merocyanine dye LB films, CdCl2 and KHCO3 solutions were added in subphase. From the optical absorption spectra of the mixed dye LB films (6Me-Ds:AA = 1:2) at different layers, the optical absorption peak was about 520 nm. However, the optical absorption peak of the LB films was shifted to 600 nm, when CdCl2 and KHCO3 solutions were added. This is the consequence result to the J-aggregation of the merocyanine dye. We also investigated the optical absorption peak of the LB films according to various time at 60 degrees C and 275 nm UV. We measured the STM morphology of the merocyanine dye LB film (1 layer) before UV irradiation and heat treatment. The morphology size of the LB film on HOPG was 5 nm. The roughness and molecular size were about 66.163 pm and 0.176 nm, respectively. The J-aggregation of this type was also accompanied by large morphological changes. We analyze the morphology and electrical properties of the LB films by the scanning tunneling microscopy (STM).